Troubleshooting and Repair of
Consumer Electronic Equipment

Including:
Test Equipment, Supplies, Parts, Incredibly Handy Widgets(tm),
Sources of Information, and Where to Find Broken Stuff

Version 2.47a (16-Feb-13)

Copyright © 1994-2014
Samuel M. Goldwasser
--- All Rights Reserved ---

For contact info, please see the
Sci.Electronics.Repair FAQ Email Links Page.


Reproduction of this document in whole or in part is permitted if both of the following conditions are satisfied:
  1. This notice is included in its entirety at the beginning.
  2. There is no charge except to cover the costs of copying.


Table of Contents



  • Back to Troubleshooting Table of Contents.

    Preface

    Author and Copyright

    Author: Samuel M. Goldwasser

    For contact info, please see the Sci.Electronics.Repair FAQ Email Links Page.

    Copyright © 1994-2014
    All Rights Reserved

    Reproduction of this document in whole or in part is permitted if both of the following conditions are satisfied:

    1.This notice is included in its entirety at the beginning.
    2.There is no charge except to cover the costs of copying.

    DISCLAIMER

    We will not be responsible for damage to equipment, your ego, blown parts, county wide power outages, spontaneously generated mini (or larger) black holes, planetary disruptions, or personal injury that may result from the use of this material.



  • Back to Sam's Gadget FAQ Table of Contents.

    Introduction

    Getting Into Troubleshooting

    This document attempts to provide an entry to the world of consumer electronics troubleshooting and repair. It also covers test equipment selection, tools and supplies, parts, home made troubleshooting aide - Incredibly Handy Widgets(tm) - and safety.

    Mostly, you will learn by doing. However, you do need to prepare.

    There are many schools dedicated to electronics repair. Some of these are quite good. Many are not. This document, however, is written from the perspective of the motivated do-it-yourselfer, hobbiest, and tinkerer.

    The Repair FAQs usually list suggested references for each area. Your local public or university library will probably have some of these or other repair oriented electronics books.

    Above all read and understand the document: Safety Guidelines for High Voltage and/or Line Powered Equipment. Your life may depend on it. That fabulous large screen won't be of much use to you if you are dead.

    Collect broken electronics and appliances from your friends, relatives, the dump, garage sales and flea markets, etc. Start on those that have been written off - you will screw up at first. We all did. As times passes, your batting average will improve. It may not happen overnight but it will happen if you apply yourself. There will be many relatively easy successes but the 'tough dogs' may make up for these triumphs. Don't let them get to you - not everything can be repaired. Sometimes, the basic design is flawed or someone before you messed up royally. Troubleshooting is like being a detective but at least the device is generally not out to deceive you.

    Experience will be your most useful companion.

    If you go into the profession, you will obtain or have access to a variety of tech tips databases. These are an excellent investment where the saying: 'time-is-money' rules. However, to learn, you need to develop a general troubleshooting approach - a logical, methodical, method of narrowing down the problem. A tech tip database might suggest: 'Replace C536' for a particular symptom. This is good advice for a specific problem on one model. However, what you really want to understand is why C536 was the cause and how to pinpoint the culprit in general even if you don't have a service manual or schematic and your tech tip database doesn't have an entry for your sick TV or VCR.

    While schematics are nice, you won't always have them or be able to justify the purchase for a one-of repair. Therefore, in many cases, some reverse engineering will be necessary. The time will be well spent since even if you don't see another instance of the same model in your entire lifetime, you will have learned something in the process that can be applied to other equipment problems.

    As always, when you get stuck, the sci.electronics.repair newsgroup will still exist!

    Happy repairing!

    Comments on How to Learn Repair

    (From: Nicholas Bodley (nbodley@tiac.net).)

    Here's how I see it:

    By all means, do what you can to understand basic principles first. Your success will be much more likely when you understand how a device works. If you can, read Electronics Now and Popular Electronics, as well as Nuts and Volts (http://www.nutsvolts.com/). Also have a look at the Radio Amateur's Handbook.

    These periodicals are not carefully edited, unfortunately, and now and then things get into print that are simply wrong or misleading, but they are still useful; I learned quite a bit from their predecessors (Radio Craft and Radio News!).

    I can't speak firsthand, but it might be a very good idea to become (eventually) a Certified Electronic Technician. Look up the I.S.C.E.T.

    Hearsay and folklore sometimes indicate that you should replace a given part when certain symptoms occur, and in the case of frequent failures of such parts, this information might even be true. But that's no way to become a competent technician.

    My personal take is that you have to know when to 'let go' of an hypothesis about what the cause of the trouble is. A tech. who persists beyond a certain point in his belief that such-and-such is causing the problem is stuck and spinning his wheels. (I'm sexist; I think women are far less likely to get stuck this way! I think it's a male trait. :)

    Troubleshooting is a special field of knowledge and has its own special outlook on things. The device did work, after all.

    Production testing and troubleshooting is different; you are likely to be the first person to apply power to a device, and the device has never worked before. If the assemblers aren't giving you excellent quality, you can have some remarkably-bizarre symptoms with a poorly laid-out board from solder shorts, for instance.

    A variable toroidal autotransformer (universally known by what used to be a General Radio trade-name, Variac) is priceless for troubleshooting circuits that handle any amount of power and which are powered by the AC line. (Not all devices function at all at, say, half of rated AC input; I work on a poorly-designed amplifier that draws many amps at something like 70 volts with no signal and no load. Unfortunately, Variacs and their equivalents are horribly expensive, at least from some sources! If you get a used one, see that the contact area of the winding is undamaged; you might need to remove a knob and some covers to see it. If the knob is stiff, try some contact/control cleaner/lube; it did wonders for mine!

    Learn how to operate a 'scope, and learn why you see what you do. I suspect that some techs are not too well-informed about what goes on inside a 'scope; learn from reliable sources!

    Learn to use a digital multimeter, and an analog one as well; the latter is easily damaged if you don't know what you're doing, but it's a great trend indicator.

    Learn to use a function generator, and use the triangle output as well! Nothing like a triangle to show a wee bit of clipping or limiting in an amplifier...

    Learn how to solder! Solder is not an adhesive; it's a metallurgical bond, according to some sources I trust. It just about has to be with gold, at least! If you *really* want to learn soldering, NASA has developed training courses that will make you a disgustingly good solderer.

    (From: Phillip R. Cline (pcline@iquest.net).)

    I used to repair consumer electronics from VERY high end stereos down to lowly boom boxes. When repairing stereos there is no substitute for good troubleshooting techniques which come from empirical means. Good knowledge of circuit functions helps a great deal. VCRs are almost always a mechanical problem (70% or more in my experience). Audio stuff can be destroyed by the user and often times the design is just plain crap. All low and mid-fi Japanese stuff made within the last ten years isn't worth a crap from a design standpoint. Even a lot of the high-end stuff is junk. They have 71 volt rated caps running at 69 volts etc.... US and most European stuff is way better designed! There are exceptions. I once saw a Philips amp that had a transformer for the power amp supply that wasn't centertapped yet the supply was bipolar. They just rectified and filtered the AC with series caps and the common was the point they were connected to each other. This is fine if you rate the caps at more voltage than the power supply can deliver but these were rated at just over half the total voltage of the supply from rail to rail. One cap shorted and the other one exploded and launched the can sideways across the component side of the amp PC board. This basically did a nice job of depopulating the board along the ballistic path of the cap's can. I laughed for a good while after seeing this.

    I gave up repairing stuff when the customers asked, and rightly so, why it costs $80 to fix something that costs $100 new. The OEM parts cost on some stuff was intended to make the customer go buy a new unit instead of repairing the old one. This basically made most of the stuff disposable.

    My background was and still is as an electronic hobbiest so the theory of operation was not a big deal and circuit function wasn't either. I have a brother that was the person from whom I learned a great deal of what I know now about electronics.

    Soldering ability cannot be overstressed in importance especially with SMT being very common nowadays. As for the guys that seem to be ripping you off in their pricing, they could be gouging you but most often the overhead in the shop and their cost on parts is the most likely cause of high pricing. While labor might seem high a great deal of repair can be accomplished in an hour by a competent technician and some shops have a flat rate for a given repair. This can work to the benefit of the shop sometimes and to the customer sometimes. Our shop was this way. We had the lowest pricing in town(Indianapolis) and the customers still bitched. Sometimes they would take their units after we gave them the price for labor and a estimate of parts cost. We didn't charge for estimates. They would storm out only to come back with their tail between their legs in a few days after checking around for labor charges elsewhere. Depending on their attitude we might go ahead with the repair. Often times we would decline by telling the customer that the other shops may have done something while checking the unit out.(This depended on the shop that the customer took the unit to.) Some of these places had some real winners for techs!! We really didn't feel like undoing some yoyo's handiwork just to get the unit back to it's original nonworking state!

    An EE in electronics is useless by itself and will cause a lot of undue troubleshooting to the beginning tech. They will overlook the obvious easy stuff for some possible but unlikely fault. A few years of repairs under their belt though and they can find the most difficult electronic problems with relative ease.

    The best way to become proficient is with hands-on training under an experienced tech. A good overall background in electronics doesn't hurt either.

    (From: Michael Black (blackm00@CAM.ORG).)

    I think one of the problems of home repair is fear. If you're willing to spend the money to have something repaired, then you may think that if you fiddled with it you may make it worse. On the other hand, if you are about to throw something out because it doesn't work, you have nothing to lose by playing around with it and trying to fix it. Or find some stuff other people have thrown out, and start with that.

    You may not fix it, but your willingness to open the cover allows you a familiarity that you won't get from a book. You de-mistify the equipment, and by actually adjusting things and seeing the results, you will learn.

    I picked up a VCR for cheap at a garage sale this past summer. I was buying it as a tuner for use with a monitor. The guy said it "must be the power supply because it keeps turning off". Actually, it kept turning off because the mechanics weren't working properly. By moving the parts by hand, I saw how they were supposed to work. With the first hand experience, the S.E.R FAQ made more sense than if I'd just read it first, and so did a book on VCR repair that I took out of the library. I saw that the belts needed replacing because I'd figured out how things were supposed to work, and saw that they weren't working that way.

    (From: Malcolm MacArthur (malcolmm@rustic-place.demon.co.uk).)

    I have two years' of an Electronic Engineering degree behind me (I gave up on the degree and became a computer programmer. ;) It has been little, if any, help. What you really need is experience... which you'll only gain by fiddling with things. I've been doing repairs since about age 13. After twelve years, I now have a fair success rate, but those first few years were not easy. Best thing to do is get hold of old equipment and just have a go with it (Beware of CRTs, though ;). Be warned, you may break quite a lot of stuff initially! But as the others have said, most of the problems are due to mechanical failures (including dry solder joints).

    Tall repair stories time:

    As you can see above, most of these repairs are pretty simple and can be accomplished with mechanical know-how, more than anything else. Be prepared to experiment - but also be prepared for the fact that some of your experiments might fail! I guess I've just been lucky, but few of my repairs even involved using a multimeter.

    Have fun.

    THE Question: To Repair or Not to Repair

    One of the themes, repeated more than once in emails to me and in reader feedback from Poptronix/Electronics Now was of the following general flavor:

    "Why bother with repair of VCRs (or anything else) when I can buy a new model for $79.95?"

    Actually, I've seen prices as low as $39.95 for a promotion (but not requiring the purchase of anything else)!

    or:

    "This stuff may have been useful 5 years ago but now some/much of the material doesn't apply to newer VCRs."

    While both of these deal with VCRs, it should be understood that it applies equally well to much other consumer electronics.

    Depending on your background and interests, these statements may have some validity. Thus, the need for some objective (if possible) way of making a decision as to whether to bother at all, and whether to attempt the repair yourself.

    So, when does it make sense to attempt *any* repair yourself rather than to toss the item in the trash or take it to a professional? People do this sort of stuff for several reasons:

    1. For the challenge and rewards associated with success.

    2. To save money.

    3. Because they like a particular set of features or the controls or the styling of the equipment and don't want anything new!

    4. To avoid cluttering land-fills.
    The first of these is likely most relevant to the readers of the S.E.R FAQs.

    It's quite difficult to suggest an approach in deciding when something is worth repairing. You have to decide how much the equipment is worth to *you* in terms of monetary, sentimental, or other value; how much time you are willing to put into a repair; and whether the failure represents a good excuse to upgrade! To what extent each of the factors is significant will also be determined by how much you enjoy troubleshooting and tinkering. If you'd rather be doing something else or keep thinking about all the time you are spending on this rather than something you can charge for, perhaps you should be doing that something else.

    However, it is easier to identify specific situations where equipment probably *isn't* worth attempting to repair on your own (or possibly at all):

    1. Serious damage due to water (especially salt water), fire or smoke. Even if the obvious faults can be found and corrected, there are likely to be latent failures just waiting to strike in a few weeks or months.

    2. Lightning strike. Lightning is like the 900 pound gorilla - it can go anywhere it wants. Even if you can repair the obvious damage and get the equipment working, there could be hidden problems waiting to appear at a later time due to components that aren't totally fried but just weakened.

    3. Extremely high electrical power surge like a 13,000 V feeder line falling across the 115 V wiring to your house. Similar comments as lightning apply.

    Where any of these are covered by insurance, that is the best option where the settlement is at all reasonable. If the insurance company allows you to keep the damaged equipment, there is nothing to stop you from attempting repairs as a challenge - you may get lucky. But, it could also be a long drawn out and expensive frustration.

    1. Serious physical damage, especially for equipment with mechanical parts like VCRs. It may be impossible to replace broken parts. Twisted metal can be straightened but there is a good chance there will still be erratic misbehavior.

    2. Equipment where prior attempts at repair may have resulted in an undetermined number of new unidentified problems. At least when something breaks on its own, your only opposition is the device itself. But, if another person attempts a repair and they are a novice or just plain incompetent, the dumpster may be the best solution.

    3. Equipment with known design or manufacturing problems. When we undertake a repair, one assumption that is usually made is that the equipment originally worked correctly and/or that the fault isn't something that was designed in before the name went on. :) For most things, this is a valid assumption. Even the famous RCA/GE/Proscan and Sony TV solder problems, while no doubt resulting in 100s of thousands of sets ending up in the trash, are repairable with modest effort at low cost. And, the result is a well performing reliable TV. However, some computer monitors may die when fed a particular scan rate or during boot when mated with a particular video card - a design flaw which may not have a (known) solution.

    4. Newer throw-aways. I can pretty much guarantee that a $39.95 VCR isn't worth any effort unless the problem is obvious. This junk is built as cheaply as possible with a lot of plastic parts, no thought given to access for testing or repair, and with attention only to the short term bottom line. There has been no miraculous invention to reduce construction cost of the relatively complex VCR mechanism - it comes out of reliability.

    5. Equipment like cell phones, pagers, and other modern wireless devices as well as cordless phones; PC mainboards, peripheral boards, and disk drives; TV set-top, cable boxes, satellite receivers, etc. It is essentially impossible to obtain service information on any of these so unless the problem is an obvious broken connector or broken trace on the printed circuit board, or possibly a dead power supply, forget it. You don't have the documentation, test equipment, rework equipment, or any chance of buying many of the repair parts in any case.

    6. Any situation where safety would be compromised by your repair. For example, attempting to reconstruct a smashed microwave oven door or jerryrigging a flyback transformer that has serious arcing. Where items (1) to (3) are involved, one must very carefully inspect for any possible safety related damage (like charred insulation in hidden areas) that may not have affected operation.

    7. If you really don't know what you are doing, leave it to a professional! Not only is it dangerous to be poking around inside many types of equipment if you don't even know what not to touch, there is a strong likelihood that such attempts will cause additional, possibly fatal damage to the circuitry. Even if the equipment can be repaired, the ultimate cost will end up be much greater than had you not done anything in the first place, both in terms of labor (troubleshooting and repair) and parts. If you can't justify a professional repair, just set it aside until you have gained more experience and can deal with the equipment safely (for you and it).

    8. Finally, don't attempt to repair a piece of equipment for which you are not equipped in the tools or test equipment department. Attempting to remove a part from a multilayer printed circuit board without proper desoldering equipment will just make an unsalvageable mess. Guessing at a replacement part ("I heard that the flyback transformer is a likely cause for a dead monitor.") will just end up being frustrating and expensive (unless you've won the Lottery recently in which case maybe your luck is still holding).

    In the good old days when life and electronics were simpler and you could count the total number of transistors in a TV on your hands and feet, service information was included with the equipment or was readily available either from the manufacturer or Sams Technical Publishing (formerly Howard Sams) as Sams' Photofacts (no relation to me). There are still Sams' Photofacts for many TVs at least, but for anything else, obtaining schematics may be impossible or even if they are available, the cost may be excessive. Paying $100 for a mediocre copy of a service manual for a computer monitor that can be replaced for $250 may not be justified.

    One way to get an idea of your chances of success for popular brands and models is to search the archives of the USENET newsgroup sci.electronics.repair via Google Groups (formerly Deja.com/Dejanews. There are other public USENET archives but even though this archive keeps changing its name, I see little reason to use others which may come and go and provide less reliable coverage.) Where others have experienced - and repaired - similar problems, your chances of success are greatly increased. Then, if you have detailed symptoms, asking for suggestions on that newsgroup may also be beneficial, especially if you have already done some initial testing. If, on the other hand, the consensus from the newsgroup is that your problem is hopeless, then you may be able to save a lot of time and frustration by giving up immediately (or at least postponing your efforts until you have more experience.

    What about older equipment?:

    The basic technology of TVs and VCRs hasn't changed significantly in 10 or 15 years. Yes, there are convenience features like "auto clock set" which are supposed to make life easier but often don't (if the station transmitting the clock information has their clocks set wrong or uses a feed from a source in a different time zone!). But as far as picture and sound quality, that VCR from 10 years ago will be just as good or better than one purchased today. Any, it will almost certainly be better constructed and more maintainable.

    For example, Panasonic VCRs from the mid to late '80s were solid machines that could be kept in shape with a bit of periodic maintenance (cleaning, rubber parts replacement) and repair of known problems (failed electrolytic capacitors in the power supply after 10 years or so). One could not expect that $39.95 special to provide such service. If it lasts through the warranty period, you're probably ahead of the game. I'd still take a middle age Panasonic over any new low to medium priced model. And, even the high-end VCRs may be based on flimsy chassis.

    Case studies:

    Here are 4 examples of equipment that I did eventually repair but where serious consideration should have been given to the dumpster. The following can be found described in more detail at in the document: Sam's Repair Briefs/

    1. GE TV dropped: (From: Repair Brief #69: GE Portable Color TV - Dropped.)

      This TV had taken a nose dive off of a 4 foot shelf onto an unknown surface. And, of course, someone had probably attempted to operate after this with possible additional damage. While the exterior didn't show any major abuse, it was obvious that there was severe trauma as soon as the back was removed. The main circuit board was broken near the (heavy) flyback transformer. Several dozen traces were severed including some to surface mount parts.

      A repair shop would be unlikely to want to tackle this for several reasons: (1) the obvious repairs to circuit board traces would take a couple hours at least, (2) there could be unseen damage to the CRT in form of a distorted shadow mask and this wouldn't be known until the circuit board was fixed, and (3) any repair might not catch everything so future problems could develop.

      As it turned out, the only damage was to the circuit board and after 2 or 3 hours of soldering - and then finding additional traces to solder - the set was fixed, and has continued to operate reliably for many years.

    2. GE TV with 'rivlets': (From: Repair Brief #59: GE 13AC1504W Color TV - Dead (with Other Problems)).

      In the early 1980s, some brilliant manufacturing engineer working for GE decided that a good way to save money on circuit boards would be to use what were dubbed 'rivlets' instead of actual plated through holes to connect top and bottom. A rivlet is basically a rivet which, the theory goes, is then soldered to the copper traces. That's the theory. In practice, due to the thermal mass of the rivet, soldering was never reliable. And, as a result of thermal cycling, cracks developed between the rivet and traces over time. Problems ranged from a dead set to loss of color depending on which rivlet happened to be unhappy on any given day.

      Attempting to repair just the problem rivlets was impossible because as soon as you found a bad one and soldered it, another in its vicinity would decide to fail. The only approach that worked was to reheat every one that could be located using a soldering gun. Since there were many dozens of these on the circuit board, this took quite awhile and it was easy to miss some. In fact, the only truly reliable repair would be to remove the solder from each rivlet, snake a bare wire through it, and solder the wire directly to the traces top and bottom. This repair would also take a couple hours and likely be too expensive for a small TV, though if the same chassis were used on a 27 incher, might be worth it.

    3. CD player restoration: (From: Repair Brief #10: Pioneer PD5100 CD Player Trashed).

      Here is a case of a piece of equipment being partially destroyed by previous repair attempts. The Pioneer PD5100 is a basic solid CD player but this one had broken parts in the loading mechanism and was in unknown operational condition. If it were taken to a repair shop, the response would probably be something along the lines of: "Well, that certainly looks like a CD player.". It simply wouldn't be worth the time and effort to repair what was obviously broken with the possibility of finding more serious electronic problems after that.

      I had nothing better to do (!!) so decided to attempt to restore it to something usable. After repairing the mechanical damage, there was indeed a servo problem which ultimate required the replacement of a motor driver chip - for which I got lucky. The player would read the disc directory but was unable to seek to any track, even #1. One of the chips was getting hot. So, I replaced it and after servo alignment, the play problems were cured. If that hadn't worked, there was probably little more I could have done. Very likely, the servo chip was the original problem and the previous repair attempt created the mechanical mess.

    4. Sony TV with bad butchered soldering: (From: Repair Brief #81: Sony KV-19TR20 Color TV - No Reception).

      The final example is of a Sony TV that had the infamous tuner/IF box solder problems. This is normally a fairly easy repair, especially for this particular model where the IF box (which was faulty in this case) is readily accessible without taking the whole thing to bits. Once repaired, like the RCA/GE/Proscan TVs with similar solder problems, the result is a solid reliable TV. However, the friend of a friend who had attempted to replace it, apparently used a Weller soldering gun to do the fine soldering, leaving nearly every pad detached or missing. Fortunately, only the pads appeared to have suffered and after 20 minutes and several jumper wires, this one was healthy again.

    Repairs for the novice:

    It would be way too easy to poison your future outlook on servicing by attempting repairs multiple times and failing or making things worse.

    Equipment that is good to learn on because there will likely be immediate or at least ultimate gratification might include: small appliances, power tools, remote controls, and basic audio equipment like tape decks and low power amplifiers (not big power amps!). And, while electronic troubleshooting of CD players and VCRs is definitely for the advanced course, they often have problems that can be easily remedied by a proper cleaning and/or general maintenance. Electronic problems are tough to diagnose but most are mechanical. Microwave ovens are generally easy to repair but due to the very serious safety issues, I'd suggest holding off on these unless you are experienced in dealing with high voltage high power equipment.

    With reasonable care, PC troubleshooting involving basic swapping of components, can also be rewarding. But, don't expect to repair a mainboard with a peculiar failure of IRQ2 (unless you find a lockwasher that ate through to some PCB traces!).

    Intermediate level troubleshooting and repair would add TVs since service information in the form of Sams' Photofacts is available for the majority of popular models. Video (not computer) monitors are also straightforward to deal with. And perhaps, audio amplifiers and receivers.

    For those just starting out, there are some types of equipment to avoid (beyond those mentioned above). One in particular is modern computer monitors. With their wide scan rate range, microprocessor control, need for decent test equipment, dangerous voltages, and the general difficulty in obtaining service information, even professionals will stay away from many of these - particularly no-name or non-major brand models. Except for obvious problems like bad solder connections, a blown fuse (replace ONCE only, might have been a power surge), or the need for degaussing, they may not be worth the frustration, certainly not as your first project. TVs are not only much simpler than computer monitors, but as noted, complete service information is usually available.

    If You Decide That You Don't Want to Bother Repairing Something

    So, you already have 10 VCRs and really don't want to even pop the case on yet another one.

    Don't just toss it in the trash. See if a local charity like the Salvation Army or Goodwill accepts broken appliances and electronics. They may have someone on staff who can perform at least simple repairs and then resell the item. Not only will this reduce clutter in the land fill, you may benefit on your taxes (and in the good deeds department). However, it really isn't proper to do this if you have already worked on the item and given up or reduced it to a pile of slag!

    Smoking Around Electronic Equipment

    Note: This is my token editorial but the effects on both people and equipment are very real.

    If you still doubt the harmful effects of the chemical compounds in tobacco smoke on your health and that of others around you, whatever I say below probably won't matter and you may want to skip it since it may upset you. However, perhaps, you worry more about your fancy, costly, finely tuned electronic entertainment and computer equipment. In that case, read on.

    The several hundred chemical compounds found in tobacco smoke have the following effects on electronic equipment. What isn't trapped in your lungs or in the lungs of those around you:

    This list of effects goes on and on.

    The resulting film WILL eventually cause problems and is very difficult to remove. Damage done due to chemical action may require the replacement of costly parts. Increased maintenance will be needed or the equipment may simply fail before its time and not be worth fixing. Contamination will often find its way into critical places that are not accessible and to media which is irreplaceable.

    When someone trys to get me to look at something that has been in a smoker's residence (I know because it will reek of stale tobacco smoke essence), my first inclination is to put it in a sealed bag to go out with the garbage. (I have been known to drop portable TVs directly into the nearest trash can under these circumstances.) If this isn't an option, my next objective is to get it evaluated and repaired or refused as quickly as possible. However, my concentration may not be at its peak for such equipment! It is a good thing that I don't need to do this for a living - I would have to refuse service to a good portion of the world's population :-(.

    So, now you have a few more reasons to give up the stupid, disgusting, filthy, obnoxious, inconsiderate of others, costly, dangerous, killer habit!

    Sorry, end of editorial. :-)

    General Safety Considerations

    Depending on the type of equipment you will be working on, there can be a variety of dangers - some potentially lethal: It is imperative that you understand and follow ALL safety recommendations while working inside whatever equipment.

    See the document: Safety Guidelines for High Voltage and/or Line Powered Equipment for general safety information.

    See the SAFETY sections of the documents dealing with your equipment for additional safety information for your equipment.



  • Back to Troubleshooting Table of Contents.

    Basic Troubleshooting

    Some of My Rules of Troubleshooting

    1. Safety first - know the hazards associated with the equipment you are troubleshooting. Take all safety precautions. Expect the unexpected. Take your time.

    2. Always think 'what if'. This applies both to the analytic procedures as well as to precautions with respect to probing the equipment. When probing, insulate all but the last 1/8" of the probe tip to prevent costly shorts. (If I had a nickel for every time I have been screwed not following this advice...)

    3. Learn from your mistakes. We all make mistakes - some of them can be quite costly. A simple problem can turn into an expensive one due to a slip of the probe or being over eager to try something before thinking it through. While stating that your experience in these endeavors is measured by the number of scars you have may be stretching the point, expect to screwup - we all can point to that disaster due to inexperience or carelessness. Just make it a point not to make the same mistake again.

    4. Don't start with the electronic test equipment, start with some analytical thinking. Many problems associated with consumer electronic equipment do not require a schematic (though one may be useful). The majority of problems with VCRs, CD players, tape decks, and answering machines, are mechanical and can be dealt with using nothing more than a good set of precision hand tools; some alcohol, degreaser, contact cleaner, light oil and grease; and your powers of observation (and a little experience). Your built in senses and that stuff between your ears represents the most important test equipment you have.

    5. If you get stuck, sleep on it. Sometimes, just letting the problem bounce around in your head will lead to a different more successful approach or solution. Don't work when you are really tired - it is both dangerous and mostly non-productive (or possibly destructive).

    6. Many problems have simple solutions. Don't immediately assume that your problem is some combination of esoteric complex convoluted failures. For a TV, it may just be a bad connection or failed diode. For a VCR, it may just be a bad belt or idler tire - or an experiment in rock placement by your 3-year old. For a CD player, a dirty lens or need for lubrication. Try to remember that the problems with the most catastrophic impact on operation - a dead TV or a VCR that eats tapes - usually have the simplest solutions. The kind of problems we would like to avoid at all costs are the ones that are intermittent or difficult to reproduce: subtle color noise, the occasional interference, or the dreaded horizontal output transistor blowing out every 3 months syndrome.

    7. Whenever possible, try to substitute a working unit. With modular systems like component stereos and computers, narrowing down a problem to a single unit should be the first priority. This is usually safe to do in such cases and will quickly identify which unit needs work. This same principle applies at the electronic or mechanical parts level. Note that there is the possibility of damaging the known good part by putting it into a non-working device or vice versa. This risk is most likely with the power circuitry in amplifiers, TVs and monitors, power supplies, etc. With appropriate precautions (like the series light bulb) the risk can be minimized.

    8. Don't blindly trust your instruments. If your get readings that don't make sense, you may be using your equipment in a way which is confusing it. DMMs are not good at checking semiconductors in-circuit or the power transistor you are testing may have a built in damper diode and/or base resistor. Your scope may be picking up interference which is swamping the low level signal you are searching for (TVs and Monitors, or low level circuits in VCRs and CD players). Your frequency counter may be double triggering due to noise or imperfect signal shape.

    9. Realize that coincidences do happen but are relatively rare. Usually, there is a common cause. For example, if a TV has no vertical deflection and no picture, it is much more likely that a common power supply output has failed than for parts in both the deflection and video subsystems to be bad. In other words, first look for a common root cause rather than trying to locate bad parts in separate circuits.

      Exceptions include lightning, power surge, dropped, water, or previous repair person damaged equipment. However, multiple electrolytic capacitors in older equipment may be degrading resulting in failures of unrelated circuits. Determine if all the problems you are troubleshooting have just appeared - see below. It is very common to be given a device to repair which has now died totally but prior to this had some behavior which you consider marginal but that was not noticed by the owner.

    10. Confirm the problem before diving into the repair. It is amazing how many complaints turn out to be impossible to reproduce or are simple cockpit error. It also makes sense to identify exactly what is and is not working so that you will know whether some fault that just appeared was actually a preexisting problem or was caused by your poking. Try to get as much information as possible about the problem from the owner. If you are the owner, try to reconstruct the exact sequence of events that led to the failure. For example, did the TV just not work when turned on or were there some preliminary symptoms like a jittery or squished picture prior to total failure? Did the problem come and go before finally staying bad for good?

    11. Get used to the idea of working without a schematic. While service info for TVs is nearly always available in the form of Sams' Photofacts, this is hardly ever true of other types of equipment. Sams VCRfacts exist for less than 10 percent of VCR models and only the older ones include anything beyond (obvious) mechanical information. While a service manual may be available from the manufacturer of your equipment or another Sams-like source, it may not include the information you really need. Furthermore, there may be no way to justify the cost for a one time repair. With a basic understanding of how the equipment works, many problems can be dealt with without a schematic. Not every one but quite a few.

    12. Whenever working on precision equipment, make copious notes and diagrams. You will be eternally grateful when the time comes to reassemble the unit. Most connectors are keyed against incorrect insertion or interchange of cables, but not always. Apparently identical screws may be of differing lengths or have slightly different thread types. Little parts may fit in more than one place or orientation. Etc. Etc.

    13. Pill bottles, film canisters, and plastic ice cube trays come in handy for sorting and storing screws and other small parts after disassembly. This is particularly true if you have repairs on multiple pieces of equipment under way simultaneously.

    14. Select a work area which is wide open, well lighted, and where dropped parts can be located - not on a deep pile shag rug. The best location will also be relatively dust free and allow you to suspend your troubleshooting to eat or sleep or think without having to pile everything into a cardboard box for storage.

    15. Understand the risk of ESD - Electro-Static Discharge. Some components (like ICs) in solid state electronic devices are vulnerable to ESD. There is no need to go overboard but taking reasonable precautions such as getting into the habit of touching a **safe** ground point first.

      WARNING: even with an isolation transformer, a live chassis should **not** be considered a safe ground point. This applies mostly to TVs, computer and video monitors, some AC operated strobe lights, and other line connected devices. You shouldn't be touching components with the device powered and plugged in (at least, not until you really know what you are doing!). Once unplugged, sheet metal shields or other ground points should be safe and effective.

    Some Quick Tips or Rules of Thumb

    On-Line Tech-Tips Databases

    A number of organizations have compiled databases covering thousands of common problems with VCRs, TVs, computer monitors, and other electronic equipment. Most charge for their information but a few, accessible via the Internet, are either free or have a very minimal monthly or per-case fee. In other cases, a limited but still useful subset of the for-fee database is freely available.

    A tech-tips database is a collection of problems and solutions accumulated by the organization providing the information or other sources based on actual repair experiences and case histories. Since the identical failures often occur at some point in a large percentage of a given model or product line, checking out a tech-tips database may quickly identify your problem and solution.

    In that case, you can greatly simplify your troubleshooting or at least confirm a diagnosis before ordering parts. My only reservation with respect to tech-tips databases in general - this has nothing to do with any one in particular - is that symptoms can sometimes be deceiving and a solution that works in one instance may not apply to your specific problem. Therefore, an understanding of the hows and whys of the equipment along with some good old fashioned testing is highly desirable to minimize the risk of replacing parts that turn out not to be bad.

    The other disadvantage - at least from one point of view - is that you do not learn much by just following a procedure developed by others. There is no explanation of how the original diagnosis was determined or what may have caused the failure in the first place. Nor is there likely to be any list of other components that may have been affected by overstress and may fail in the future. Replacing Q701 and C725 may get your equipment going again but this will not help you to repair a different model in the future.

    One alternative to tech-tips databases is to search via Google Groups (formerly Deja.com/Dejanews) for postings with keywords matching your model and problem and the newsgroup sci.electronics.repair. See the section: Searching for Information from USENET Newsgroups.

    Please see the document: On-Line Tech-Tips Databases for the most up to date compilation of these resources for TVs, VCRs, computer monitors, and other consumer electronic equipment.

    Getting Inside Consumer Electronic Equipment

    Note: the documents on specific equipment has additional 'getting inside' info as well.

    Yes, you will void the warranty, but you knew this already.

    Hint: The crowbar and 12 pound hammer are *laset* resorts! Really :-).

    Manufacturers seem to take great pride in being very mysterious as to how to open their equipment. Not always, but this is too common to just be a coincidence. Opening the equipment non-destructively may be the most difficult and challenging part of many repairs!

    A variety of techniques are used to secure the covers on consumer electronic equipment:

    1. Screws. Yes, many still use this somewhat antiquated technique. Sometimes, there are even embossed arrows on the case indicating which screws need to be removed to get at the guts. In addition to obvious screw holes, there may be some that are only accessible when a battery or cassette compartment is opened or a trim panel is popped off.

      These will often be of the Philips variety. (Strictly speaking, many of these are not actual Philips head screws but a slight variation. Nonetheless, a Philips screwdriver of suitable size will work on them.) A precision jeweler's screwdriver set including miniature Philips head drivers is a must for repair of miniature portable devices.

      Sometimes, you will find Torx or a variety of security type fasteners. Suitable driver bits are available. Sometimes, you can improvise using regular tools. In the case of security Torx, the center post can usually be broken off with a pair of needlenose pliers allowing a normal Torx driver to be used. In a pinch, a suitable size hex wrench can substitute for a Torx driver. Places like MCM Electronics carry a variety of security bits.

    2. Hidden screws. These will require prying up a plug or peeling off a decorative decal. It will be obvious that you were tinkering - it is virtually impossible to put a decal back in an undetectable way. Sometimes the rubber feet can be pryed out revealing screw holes. For a stick-on label, rubbing your finger over it may permit you to locate a hidden screw hole. Just puncture the label to access the screw as this may be less messy then attempting to peel it off.

    3. Snaps. Look around the seam between the two halves. You may (if you are lucky) see points at which gently (or forcibly) pressing with a screwdriver will unlock the covers. Sometimes, just going around the seam with a butter knife will pop the cover at one location which will then reveal the locations of the other snaps.

    4. Glue. Or more likely, the plastic is fused together. This is particularly common with AC adapters (wall warts). In this case, I usually carefully go around the seam with a hacksaw blade taking extreme care not to go through and damage internal components. Reassemble with plastic electrical tape.

    5. It isn't designed for repair. Don't laugh. I feel we will see more and more of this in our disposable society. Some devices are totally potted in Epoxy and are throwaways. With others, the only way to open them non-destructively is from the inside.
    Don't force anything unless you are sure there is no alternative - most of the time, once you determine the method of fastening, covers will come apart easily If they get hung up, there may be an undetected screw or snap still in place.

    The most annoying (to be polite) situation is when after removing the 18 screws holding the case together (losing 3 of them entirely and mangling the heads on 2 others), removing three subassemblies, and two other circuit boards, you find that the adjustment you wanted was accessible through a hole in the case just by partially peeling back a rubber hand grip! Been there, done that. :(

    And on the still lighter side, from an IBM maintenance manual, circa 1925 (displayed in the Chicago Museum of Science & Industry):

    "All parts should go together without forcing. You must remember that all the parts you are reassembling were disassembled by you. Therefore, if you can't get them together again, there must be a reason. By all means, do not use a hammer."

    When reassembling the equipment make sure to route cables and other wiring such that they will not get pinched or snagged and possibly broken or have their insulation nicked or pierced and that they will not get caught in moving parts. Replace any cable ties that were cut or removed during disassembly and add additional ones of your own if needed. Some electrical tape may sometimes come in handy to provide insulation insurance as well.

    For those hard-to-open LCD panels:

    (From: Onat Ahmet (onat@turbine.kuee.kyoto-u.ac.jp))

    The LCD display housings are usually secured by plastic catches built into the case. They still may have a couple of screws that are positioned in the most innovative places! Obvious places are sides of the display, and under stickers (rub your finger over a sticker and see if you can feel the hole for a screw). Also, try to look around the hinge connecting the LCD to the main housing. Look with the LCD closed, and also open; rotating open the housing might hide some screws from view. Expect it to be awkward! BTW, do not forget small hatches, that do not look like one!

    After that, it is patience, and knowing the right place to twist the case to pop it open. Try not to use screwdrivers; they leave unsightly marks along the seam.

    Also, if it is your own unit, and you break a few of the catches along the way, do not worry; you can put the housing back together with a few spots of adhesive.

    How to Build Obsolescence In Before the Name Goes On

    The following would belong more in the humor department if it weren't for the fact that much of it is true by accident or design with modern appliances and electronics! However, memorizing this list will go a long way toward helping to understand why the piece of !@#$ is such a pain to repair! I don't believe we are divulging any secrets here - the manufacturers already have this list in their "Corporate Operations Manual". :)

    These are in no particular order.

    (Portions from various people including Alan Liefting, Heath Young, Craig Osborn, Phil Allison, Franc Zabkar, Ray Chandos, and Sam.)

    1. Place metal shields around the power supplies without holes for air circulation. This will ensure power supply capacitors will dry out and make the power supply fail prematurely. And make sure not to use high temperature capacitors. Keeping the electros hot makes the ESR lower so cheaper ones will do.

    2. Push as many capacitors as possible into the sides of heatsinks, power transistors, regulators, and power resistors - anything hot!

    3. Do not bother with putting thermal conducting paste between heat sink and transistor. It only oozes and dries out anyhow.

    4. Do not bother to solder the heavy components or joints subject to thermal cycling. Touch up selected connections by hand? You have to be joking.

    5. The following components can be left out during manufacture: protection zener diodes, VDR's, spark gaps, decoupling capacitors, ferrite beads etc. If it works most of the time without them, the expense can't be justified.

    6. Keep all factory tests as short as possible. If there isn't a dirt cheap solution to any problems found, don't test for them.

    7. Buy the cheapest components from manufacturers who cannot guarantee the longevity of their product. It is easy to have a CRT fail within three years by using impure materials. This will make the cathodes oxide and reduce the emissions giving a dull, hard to read picture. The customer won't realize their TV or monitor has deteriorated but will see newer models with bright vibrant colors and just have to buy one.

    8. Fit the so-called head cleaning device to VCR's. This will ensure numerous service calls increasing the customer frustration which will lead them to buy a new product. There is one born every minute.

    9. Dispense with EMI/RFI components in the power supplies. As well as producing unacceptable interference, this will also mean that the power supply is more prone to damage from voltage spikes. These problems are by definition the responsibility of the customer anyhow so the result will only be a positive effect on the bottom line.

    10. Use the softer plastics rather than the more wear resistant phenolic for kettles and toasters. This will guarantee the consumer will purchase a new product to replace the shabby appliance.

    11. Make the covers of heat generating appliances out of painted instead of chrome-plated sheet metal. The paint will darken unevenly with use resulting in an old looking appliance in need or replacement.

    12. Do not use spot welding on your heating elements. Spot welding makes a reliable connection. Crimped connections will fail within a short period. This is good (for the manufacturer) since spare parts are not available. The consumer will have to buy a new product and have been conditioned to not expect appliances to be repairable. People like to buy new things anyhow.

    13. Install an Appliance Leakage Circuit Interrupter (ALCI) on the cord of the appliance. This is a one time use GFCI (or what I call a GFCK - Ground Fault Circuit Killer). When constructed with suitably cheap parts, it, rather than the appliance will fail but the customer will be informed that they must have gotten the appliance wet.

    14. Use the cheaper carbon film resistors instead of the more reliable metal film resistor with better voltage ratings. What the customers can't see won't bother them.

    15. Fasten heavy (or just random) parts to the PCB with that white/beige glue that decays after awhile to brown and conductive causing all sorts of nasty problems.

    16. Use a design style which will rapidly look dated. This is another ploy in order to have the consumer purchase the latest style regardless of whether the item is working or not. People are slaves to fashion - and they love slaves.

    17. Reduce the number of service agencies and the number of products the service agencies will repair for you. This will increase the sale of new products by frustrating the consumers efforts in order to have their item repaired.

    18. Fit fast blow fuses inside sealed double insulated appliances that will fail from metal fatigue. (Why did they do this??? - it was sealed with heatshrink onto one of the wires?!)

    19. Manufacture equipment as a collection of modules - example. Optics train in certain models of projectors - instead of replacing just a hot mirror ($15 or so) you have to replace the lot! (All optics and LCD screen etc as a module) Now, try getting the poor serviceman to explain why the projector that cost the customer $5,000 costs $3,000 to fix.

    20. Encourage consumers to purchase the cheapest items so when someone does make a good product, no one will buy it, and the company will go out of business.

    21. Make your spare parts very expensive or do not bother with having spare parts available.

    22. When the prototype has been built and working correctly, start removing components until it fails to work properly. Then manufacture it with the minimum parts required to make it work. In mid production run, change selected over designed components to their border line equivalents.

    23. If a government regulating agency forces a major recall due to a severe fire hazard, close the current brand name, and start a new brand with a redesigned outside shell that emulates an ergonomic look but with the same internals as before. Add words like "New, Improved, Upgraded, and Leading Edge" to the new marketing slogan.

    24. Don't make service manuals or circuit diagrams available. If you do, ensure that only your service agents get one, or price them so highly that the job becomes uneconomical. Think of it this way: Instead of buying the equipment which was the usual way of doing business in the past, the purchase price is now actually only a rental fee for the duration of the warranty. After that, the manufacturer may let the smoke out at any time without notice and thus there is no reason to support repairs. :)

    25. Don't identify yourself as the manufacturer. Hide behind your OEM resellers who of course will have no facilities to repair anything except by total replacement.

    26. Scrape the numbers off your IC's, or have them stamped with obscure in-house part numbers. You don't want to make repairs too easy for the end user or for a third party repairer who would otherwise be able to source these $1 garden variety parts from any electronics store.

    27. Don't stock parts that could reasonably be expected to fail or wear out like battery contacts, flex PCBs, remote control keypads, curly cords. If you must supply them, then do so as part of a complete, uneconomically priced assembly.

    28. Use flimsy non-standard (and hence unavailable) connectors for attaching expensive proprietary AC adaptors, chargers, and accessories.

    29. Use expensive sealed units which cannot be opened for service without being damaged, and which are powered by an inexpensive internal battery.

    30. Have a single solid wire between circuit boards and anything that moves, e.g. sockets at the back of VCRs, or almost any part of a remote control, especially the battery connection. This means that the soldered connection will give up.

    31. Have flimsy hinged flaps on a remote control that break after a short time.

    32. On a remote control, have rows and rows of identical buttons that have functions that are almost never needed. Also omit functions that would be very handy.

    33. Make sure the coax to the tuner of the VCR or TV has no proper mechanical anchorage to the chassis so it takes little more than the house cat to trip on the cable and yank the active innards from the tuner.

    34. Make sure all large metal components (particularly the audio in/out sockets at the rear of amplifiers) are only soldered to the same degree as the flimsy IC pins - just soldered sufficiently to pass the production final test.

    35. Don't use fiber reinforced plastic gears if you can use plain plastic types.

    36. Never use keys to lock shafts to plastic pulleys.

    37. Always use etched copper film thin ribbon board interconnects wherever there is maximum flexing such as in laptop screen hinges.

    38. Never make rubber drive belts accessible by just removal of the back plate.

    39. Use as many non-standard components as possible.

    40. Don't use 2 boards if you can mount components on both sides of one board.

    41. Always use the smallest possible wattage for a resistor: if the dissipation is 2 watts, then use a 2 watt resistor.

    42. Take advantage of exciting new legislation in creative ways to make it illegal for others to make compatible user-replacable parts. No more third party batteries, inkjet cartridges, etc.

    43. Add useless complexity to accessories like batteries and inkjet cartridges to make it more difficult for third parties to manufacture replacements. Include warnings about the risks of using third party accessories.

    44. Shorten product introduction cycles so that by the time the end-user requires a repair to the item, it's already obsolete.

    45. Set the cost of the repair to greatly exceed the cost of a new model of the same type of equipment, which, you just happen (surprise surprise) to have in stock and for sale.

    46. Secure battery compartment covers, cassette tape doors, and other access openings with brittle plastic tits that readily bust off when even looked at askance, much less flexed in normal operation. Carefully place these delicate plastic projections so that, when broken, they thereafter render the entire product unusable. Be sure they emanate from the main cover or chassis of the unit, rendering it infeasible to replace--in case anyone does try to replace it, price the main cover just under the retail price of a whole new product. Also be certain to design these tits thin and brittle enough to bust off after the first or second use, and from a type of plastic that is incompatible with all available plastic cements, in case anyone tries to repair them.



  • Back to Troubleshooting Table of Contents.

    Tools, Test Equipment, and Other Stuff

    Hand Tools

    Invest in good tools. If you are into garage sales, you can often pick up excellent well maintained tools very inexpensively but be selective - there is a lot of junk out there. In the end, substandard tools will slow you down and prove extremely frustrating to use. Keep your tools healthy - learn to use a wetstone or grinding wheel where appropriate (screwdrivers, drill bits, etc.) and put a light film of oil (e.g., WD40) on steel tools to prevent rust.

    Some basic hand tools.

    Emergency Screw Removal

    While a good quality selection of straight, Philips, Torx, and hex-head drivers should handle most screws found in consumer electronic equipment, a couple of other types do turn up and can really be a pain in the you-know-where to remove intact. See the section: About Those Other Funny-Headed Screws.

    It may be possible to remove such screws even if nothing in your driver assortment quite fits (short of buying the proper tool, that is - what a concept!). There is also the situation (very common) where someone (we won't say who) has pre-mangled the screw head! Here are a few approaches to try when you are stuck at 2:00 AM on a Sunday morning with an uncooperative screw:

    1. Select a driver type (usually Philips) and size that privides the best grip. Then apply as much pressure as is safely possible without destroying anything and attempt to turn the screw. What you want to avoid is slippage - once the blade slips, the head will be quickly destroyed and then you are left with options (2) or (3), below. For a jeweler's type screwdriver, clamping something larger to its shaft can provide valuable additional leverage.

    2. Use a hand grinder (e.g., Dremel tool) or thin file to create a slot in the screw head which one of your straight-blade screwdrivers will fit. Obviously, take care to avoid damage to adjacent parts and dam off the area to prevent grinding chips from getting over everything.

    3. Grab the center and edge of the screw with a pair of sharp diagonal cutters and turn it. This, of course, also damages the screw head and if you are too forceful, will break your cutters as well.

    4. Drill out the screw using a bit just large enough to sever the head from the shank of the screw. Then, use a pair of needlenose pliers to unscrew what remains. For large screws, drill only part way and then use a screw extractor like Easy-Out(tm).

    5. Superglue the screwdriver or some other suitable tool to what's left of the screw. Wait till it hardens and turn.

    6. There are also products available for the purpose of improving the grip of screwdrivers. For example: ScrewGrab.

    7. For screws into plastic holding metal covers, remove all other screws so the cover can be used to pull on the screw and heat the screw with a soldering iron. With care, it will melt its way out but the plastic will solidify to a smaller hole that can be used to install a new screw. Where the cover is also plastic, it may melt first so probably not a good idea.

    Note: some of these screws have had some material like Lock-Tight(tm) (which looks like colored nail polish) applied to the top to prevent the screw from loosening on its own. This also prevents the blade of a screwdriver from properly seating, so removal is essential before attempting removal.

    Plastic Screw Thread Repair

    Where a screw no longer tightens into a threaded plastic hole, here are a few suggestions:

    1. Install a larger screw in original worn hole. :) For repairs where the appearance isn't important, this may be the best solution.

    2. Use a soldering iron from the hidden side to "adjust" the hole. Doing this with the screw in place will result in proper threads being preformed.

    3. Fill the hole with a mixture of the same type of powdered plastic and solvent or other similar material. When dry, drill a pilot hole and then install the original screw.

    4. Glue a metal nut to the underside of plastic and use a machine screw.

    There are many other possibilities.

    To avoid this problem in the future, realize that plastic is very soft and it is essential to gently start the screw into the hole to get a feel for it properly mating with the existing threads. The use of an undersized screwdriver to get the screw started may be helpful in that it won't accidentally apply too much torque and strip the threads. Something that is less obvious is that screws for plastic are often made with a wide thread and a narrow thread wound that alternate, sort of like a deformed hunk of DNA. :) With these, there is only one proper way for them to mate with an existing hole and forcing them is asking for stripped threads and a fine strand of plastic being pulled out along with the loose screw.

    About Those Other Funny-Headed Screws

    (From: Tony Duell (ard@p850ug1.demon.co.uk).)

    As well as Phillips, there are Pozidriv and JIS:

    A Philips screwdriver won't even appear to fit a Pozidriv head. It will appear to fit a JIS head, but it will also damage it if it's at all tight. JIS screwdrivers are not easy to get, either. I think I have a small set made by Acu-Min (?).

    It's not uncommon for all 3 to be used in the same equipment, especially if subassemblies were made by different companies.

    (From: Robert McPherson (rm502@bellsouth.net).)

    There is a type of screwdriver called a "Reed & Prince" which fits these screws which are similar in appearance to Phillips screws. Cooper tools makes them.

    Workbench and AC Power

    Perhaps this isn't as immediately essential as a pair of wire strippers but for any serious electronics - be it construction or repair - some dedicated place to do it is essential. It doesn't need to be a $2,000 professionally designed "work unit". Any large sturdy flat surface will suffice as long as it doesn't need to be cleared off for meals. :)

    A size of 3 x 6 feet should be adequate, longer is better if you have the space. Workbench height is typically 36 inches. Make sure the legs are sturdy and rigid - some equipment can be quite heavy. Get yourself a comfortable stool to sit on for those marathon troubleshooting sessions.

    The surface can be laminate, particle board, plywood, butcher block, or some other insulator. It shouldn't have a dramatic pattern though since small parts will be hard to find. Wood products should have multiple coats of varnish or polyurethane. Using a cheap material that can be replaced will enable the surface to be rejuvenated after it gets pitted and burnt - as it invariably will after awhile. An antistatic surface is desirable but probably expensive to put on the entire workbench so just get an antistatic matt for use when needed. (An antistatic surface isn't quite a perfect insulator but has just enough conductivity to minimize the buildup of static electricity, essential for any work with devices like CMOS ICs and laser diodes that can be destroyed by even a small static discharge.)

    Install a shelf or shelves along the back that are about half the depth of the workbench surface to hold smaller pieces of test equipment, power supplies, parts cabinets, and other odds and ends. Add a shelf or shelves underneath for storage.

    Install AC outlets along the rear edge, vertically so debris can't fall into the holes. How many? The more the merrier - they will all get filled no matter how many are there! At a minimum, one every 6 inches or a duplex every foot, double this won't hurt. Power the workbench from two branch circuits fed from opposite sides of the 115-0-115 VAC (in the U.S.A.) Consider including at least one 230 VAC outlet (in the U.S.A.). Providing some outlets that are switched with power indicator lamps and protected by fuses or circuit breakers. Most outlets, particularly those used to plug in equipment being worked on, should be GFCI (Ground Fault Circuit Interrupter) protected for safety. But a few - clearly marked "NOT GFCI PROTECTED" - should be available for equipment that will not function reliably on a GFCI with the understanding that these lack such protection. Most test equipment and power supplies with properly wired grounded power cords do not need to be GFCI protected but won't complain if they are. However, some equipment may nuisance trip (immediately or at random) GFCIs even if functioning properly.

    The total cost can be well under $100 for all of this even if the materials and parts are purchased new. With some reasonable scrounging abilities, it can be a lot less.

    Basic Test Equipment

    Obviously, you can load up on exotic test equipment. What follows are those that are most used. You might at first not consider all of these to fit the category of test equipment but an old TV can provide as much or more useful information about a video signal than a fancy waveform analyzer in many cases. And, basic reliable easy-to-use test equipment is more important than sophisticated instrumentation laden with features you will never need.

    Jerry's Comments on Used Scopes and the Tek 465

    (From: Jerry Greenberg (jerryg50@hotmail.com).)

    If you are buying a used 465, look for the 465B. It is a better unit, and is the same price most of the time. Take care that this scope is about 20 years old, and there is no support from Tek on it. The replacement parts are not available if something blows. I used to have a few of them. One needed a CRT, and the other I sold while it was still working. For consumer electronics, you will get by with a 100 MHz unit, but it is preferable to have over 200 MHz bandwidth if you want to do front end service on consumer FM radio receivers. Read up on Nyquist and you will see the answer.

    If you also call Tektronix technical services, tell them that you are looking for a used Tek scope to be used for hobby purposes. They will be very helpful in giving you any information you require. They will even recommend models and what to look for. If you talk to their sales people, they will sometimes even give you their authorized dealers who handle used Tek equipment so that you can shop around.

    If you go a bit more for your used scope you can get a 200 or 300 MHz unit that is a newer version of an analog scope. It will have improvements over the 465 series. Look at the 2000 analog series scopes. These have a lot of enhancements like on the screen display. This will be very handy for precise work. When buying any type of scope, I would stress that the Tektronix is the best. If you find a good working used one, you will have a very high quality product, and it should give you years of service. Most of the analog scope that they made include the TV sync options.

    Even if you buy a used one, and the parts are not available, it pays then to buy a second used one and you will have spare parts. These scopes used to cost in the many thousands of dollars when new, and you are probably paying between eight hundred to fifteen hundred for a used one (somewhat cheaper now, even from surplus companies. --- Sam). These scopes will be far superior to even the newer ones from the consumer level scopes. In 1978 I believe my company paid over $8,000 for the 465B scope new. A new Chevy fully loaded was less!

    Repairing Tectronix 400 Series Scopes

    As noted above, the Tektronix 465 and 465B 100 MHz scopes are among Tek's best ever made, and very desirable and affordable for troubleshooting and general electronics work. The Tek 485 is a nice 350 MHz scope. There are many other 400 Series Tek scopes, almost any of which would make a fine service scope. However, they are showing their age dating from the '70s to the early '80s and many are appearing with power supply problems at even more affordable prices. :( :) While Tek custom parts are no longer available for these scopes (and you couldn't afford them anyhow!), many power supply problems which often result in a totally dead scope (but may also just cause specific sections like the timebase to be non-functional), can be repaired with readily available parts at little cost. And even if it turns out to be one of the custom ICs or other components, cheap parts scopes are available on eBay and elsewhere.

    The most likely causes of a totally dead scope, or one with multiple system problems, are shorted tantalum "dipped" capacitors dragging down one or more power supply rails. Apparently, Tek used a batch of unreliable caps on the some of the 400 Series scopes. While aluminum electrolytics usually just dry out with decreased capacitance and increased ESR, these dipped tantalums go short circuit. Fortunately, the design of the switching power supplies in these scopes is such that the controller shuts down from a serious overload or short rather than letting its smoke out. If the overload is on only one voltage rail and not severe (e.g., through a resistor), only that voltage may be low or absent resulting in loss of functionality or the supply may cycle on and off, but not a totally dead scope.

    So, the first step is (WITH POWER OFF) to check the resistance of each voltage test point to ground with a multimeter. While the expected resistances may not be known except from a service manual (if that), anything very low (e.g., 10 ohms) is suspect. Here are typical values measured on a Tek 485 using a Fluke 87 DMM with the black lead on ground: +50 V, 2.1K ohms; +15 V, 89 ohms; +5 V, 70 ohms; -5 V, 222 ohms; -15 V, 152 ohms. The resistance for +5 V changes significantly depending on front panel settings and which incandescent indicator lamps should be lit and may go below 35 ohms. On this scope, the -15 V rail originally measured about 10 ohms due to a bad cap. Where one of these is found, attempt to determine the location of the short to a specific circuit board. Then, trace the wiring on that board to locate the possible bad caps. A good DMM or milliohmmeter can help to track down the cap since PCB foil resistance is high enough to be measured and the resistance to ground will be lowest at the location at the bad cap. At this point, unsoldering one lead of each cap and checking its resistance is the safest approach. With care, this can be done from the component side of the board which is fortunate since removing some of these large PCBs can be a royal pain. Heat the lead with a soldering iron and pull it free. Then, use a vacuum desoldering tool ("SoldaPullet") to clear the hole. Check the resistance of the cap and/or across the supply rail to determine if you found the correct one. The bad cap mentioned above was found in about 5 minutes in this manner. There are typically only a few of these caps on each board but it's possible for the bad one to be on a board that isn't easily accessible. It may be even easier as sometimes the bad cap will have split open and thus be obviously bad. I've also heard of cases where the cap exploded and the only thing left were its legs! (The scope may even have worked fine at that point with the short removed!)

    However, any low value resistors between the power supply rail and shorted cap may become quite toasty, burnt, and carbonized, also resulting in a very noticeable stink. :) And the carbon may even short to a PCB via if there is one underneath it. :( :) I had this happen on the same Tek-485 a few years later, where it also took out a 2N2222 transistor nearby. But even though the resistor's surface was burnt to crispy carbon, when cleaned off, the resistance was still correct. (However, I did replace it.)

    Where these approaches don't work, or for the lazy but daring among us, the alternative is to apply voltage from an external adjustable current limited supply to the bad power rail. If the bad part isn't a perfect short circuit, it will dissipate heat and let its smoke out or explode (or a one of those series resistors may do so instead). Wear safety glasses! If this doesn't happen, it may actually be possible to power up the scope with the external voltage applied to determine functionality. In either case, I won't be responsible for any destroyed equipment should this be done.

    So You Can't Afford a $20,000 Transient Event Recorder?

    You know the situation - an intermittent that happens once an hour for 1/2 second! In industry, you would use a fancy logic analyzer with associated digital scope to capture the event.

    However, there may be no need for such extravagance. If you have an oscilloscope and camcorder or video camera/VCR, you probably have all that is needed.

    For a TV or monitor, point the camera at the CRT and the scope screen so that they are both in the picture and record on a 6 hour tape. Then, when your event takes place, you have a permanent record!

    That old video camera will be perfectly adequate. It doesn't need a 100X digitally stabilized enhanced reprocessed zoom or 1/10,000th second shutter. It doesn't even need to be color!

    Sure, this won't capture the 1 ns glitch. But, for the occasional flash in the picture, it is more than adequate to eliminate a video signal line as the source of the problem.

    Extensions to more convoluted problems are left as an exercise for the student!

    Transformers - Isolation and Variable

    Isolation transformers are *essential* to safely work on many types of equipment with exposed AC line connections or live chassis. Variable transformers provide a convenient way to control the input voltage to equipment to determine whether a fault still exists or to evaluate performance at low or high line voltage.

    Isolation Transformers

    An isolation transformer is very important for safely when working on live chassis equipment. Make it a habit to use an isolation transformer whenever possible. Portions of TVs, monitors, switchmode power supplies, and many other types of equipment are generally fed from a direct connection to the AC line without a power transformer (which would provide the isolation function). The DC power rails will typically be between 150 and 300 V with momentary current availability of multiple amps!

    Since Earth Ground and the Neutral of the power line are connected together at your service panel (fuse or circuit breaker box), grounds like cold water pipes, test equipment chassis, and even a damp concrete floor make suitable returns for the line voltage (Hot or live wire). Since this is just as true with the conductor being being a wire or your body, such a situation is very dangerous.

    An isolation transformer as its name implies provides a barrier such that accidental contact with an earth ground results in negligible current flow (only due to the parasitic capacitance and inductance of the transformer) - a slight tingle at worst. This also protects your test equipment as well as the device you are troubleshooting since a similar accidental contact can result in a short circuit, sparks, smoke, and many destroyed parts.

    The schematic for a typical isolation transformer is shown below:

    
                                   _        1:1
                    H o-----/ ----- _------+    +-----------o 115 V
                           Power  Fuse      )||(
                           Switch           )|| +-----------o 105 V
                                            )||(
                                            )||(
                                    Primary )||( Secondary
                Tied together at            )||(
                service panel               )||(
                |                           )||(
                |                           )||(
                +-> N o----------+---------+ |  +---+--------o Return
                |                |   4.7M*   |      |
                |                +---/\/\----|------+
                |                            |
                +-> G o----------------------+--------------o Ground
    
    

    Note: Ground is included on the secondary side. This is actually needed for safety with certain types of equipment like microwave ovens where the HV return is to the chassis. Most other consumer electronic equipment and appliances will only have a 2 wire cord and thus not use the Ground. However, a potential safety hazard can arise if some other piece of equipment develops a ground fault resulting in a live, non-isolated part being user-accessible so this must be taken into consideration in deciding whether to ground the secondary side.

    Where your outlets are only 2-prong without safety Ground, an isolation transformer will still provide most of the benefits, and if the equipment being tested has a 2-prong plug - as with most consumer electronics - it is irrelevant anyhow except for the grounding of the transformer itself.

    The high value resistor (*) is desirable to permit any static charge to leak off to ground. Since it is quite large - 2 M ohms - no perceptible current will flow between the secondary and primary sides but this value is low enough to dissipate any static charge. CAUTION: The resistor must be a high voltage rated type (as in 4,200 V isolation, large size light blue color to assure that arc over will not result due to voltage differences that may be present when the isolation transformer is being used in its normal manner.

    Although the power line Neutral and Ground wires are tied together at the main service panel (fuse or circuit breaker box), the transformer prevents any significant current flow between any of its outputs and earth ground should a fault occur.

    Even if you were standing with bare feet in a puddle of salt water on a concrete floor (noting that this is definitely NOT recommended) and were to touch something connected to the secondary of the isolation transformer or its return, or equipment circuitry attached to these, there is no direct return path for current to flow through you.

    However, this shouldn't encourage a false sense of security. If you were to touch two points at different potentials on the secondary side, you could still be fried! And some equipment like microwave ovens use their chassis, and thus ground, as the high voltage return so an isolation transformer is of limited value for these whether it passes ground through or not.

    Isolation transformers can be purchased or constructed from a pair of similar power transformers connected back-to-back. I built mine from a couple of old tube-type TV power transformers mounted on a board with an outlet box including a fuse. Their high voltage secondary windings were connected together. The unused low voltage secondary windings can be put in series with the primary or output windings to adjust voltage. See the section: Typical Homemade Isolation Transformer.

    For super critical applications like in hospitals where every microamp of leakage counts, special isolation transformers are available (no doubt at equally super cost) which have shielding between the primary and secondary to minimize the inter-winding capacitance and inductance as well. This should not really be necessary for general servicing.

    Note: Not all definitions of the term 'isolation transformer' are created equal! For some purposes, this may mean just preventing line born electrical noise from passing to the equipment. So, if you acquire something called an 'isolation transformer' on its nameplate, confirm that the primary and secondary are indeed not tied together by a low resistance. If they are, it can probably be modified for service needs by disconnecting a jumper but it may not have the insulation ratings desirable for high voltage isolation.

    (From: Filip "I'll buy a vowel" Gieszczykiewicz (filipg@repairfaq.org).)

    Ever wonder how those guys repair HV transformers running 200 kV without shutting off the power lines feeding the city? They use *very well isolated* cherry pickers! The guy on that platform is working on ONE wire which - since he's not connected to the ground - is at ZERO potential! That wire has no reference at all so no current flows. And he prays each morning that it stays that way or he goes off with a flash! [ugh!].

    You're doing something like that on a much safer level. :)

    Typical Homemade Isolation Transformer

    The schematic for a homemade isolation transformer a pair of back-to-back power transformers from ancient tube-type TVs is shown below:

                                           +-------------------------o 109 V
                                           |
                                           |     +-------------------o 121 V
                                           |     |
                                           | +---------------+
                                           | |   |           |
                              || +--o NC   | |   +---+ ||    |
                              ||(          | |        )||    |
                              ||(          | |  6.3 V )||    |
                              || +--o NC   | +-------+ ||    |
                       _      ||(          |          )||    |
           H o--/ ----- _---+ ||(          |    6.3 V )|| +--+-------o 115 V
               Power  Fuse   )|| +--o NC   +---------+ ||(
               Switch        )|| +-------------------+ ||(
                       115 V )||(                     )||( 115 V
                             )||(                     )||(
                             )||( 350 V         350 V )||(
           N o---------+----+ ||(                     )|| +----+-------o Return
                       |      || +--o NC       NC o--+ ||      |
                       |      ||(                     )||      |
                       |      ||(                     )||      |
                       |      ||( 350 V         350 V )||      |
                       |      ||(                     )||      |
                       |      |  +-------------------+  |      |
                       | Pri1 |  Sec1              Sec2 | Pri2 |
           G o----------------+-------------------------+-------------o Ground
                       | Transformer 1    2M*    Transformer 2 |
                       +------------------/\/\-----------------+
    

    Note that there should be a fuse in the primary to protect against faults in the transformer as well as the load. A slow blow type should be used in the primary circuit. The inrush current of the transformer will depend on the part of the cycle when the switch is closed (worst is actually near the zero crossing) as well as the secondary load. To protect the load, a fast blow type in the secondary is recommended. However, the inrush current of the degauss coils in TV sets and monitors, for example, will often pop a normal or fast blow fuse when no actual problems exist. (It is probably a good idea to disconnect the degauss coils while testing unless they are suspected of being the source of the problem.)

    The high value resistor (*) is to bleed away any static charge as described above.

    The power/VA ratings of the transformers you use need to be greater than your expected load. And, since some equipment like TVs and computer monitors draw a lot of current at power-on (from the degauss circuit), the isolation transformer will limit the peak current and may cause problems during startup (though overall, the limited current may prevent some types of disasters!). In any case, don't expect a pair of 6.3 VAC, 1 A transformers wired back-to-back to be useful for testing much of anything!

    Where your outlets only have 2 prongs (without safety Ground), leave out the G->Ground connection and DON'T tie the transformer cases/frames together. If the equipment being tested has a 2-prong plug, it's irrelevant anyhow except for the grounding of the transformer itself. With two separate transformers, there would have to be a fault in both to result in a safety hazard - a very low probability event.

    Also see the section: Isolation Transformers from Dead Microwave Ovens.

    (From: David Moisan (dmoisan@shore.net).)

    It's not as hard as you think to find inexpensive isolation transformers. At the next hamfest, look for someone selling dead UPS's (Uninterruptible Power Sources) or other power conditioning equipment. Isolation transformers are often sold for use in the computer industry; that's how I got mine. 250 VA for $20, and I could have gotten 1000 VA for $50 if I wanted. Definitely increases my safety *and* confidence level!

    Isolation Transformers from Dead Microwave Ovens

    The high voltage transformers from dead microwave ovens (failures are rarely due to the transformers) can also be used. These are probably much easier to locate (try your local appliance repair shop or dump) and will have a nice high capacity - usually 5 to 10 A or more.

    However, note that microwave oven transformers are usually designed with as little copper as possible in the primary winding and do go into core saturation at normal line voltage with no load. For example, measurements using a clamp-on AC ammeter of a transformer from a mid-size microwave oven shows:

                Input VAC   Input Amps
               ------------------------
                    80           .3
                    90           .6
                   100          1.1
                   110          2.0
                   115          3.0
                   120         >4.0
    
    At 115 VAC input, that's about 350 VA - probably close to 350 W with nothing connected to its secondaries! It also had a very noticeable hum above about 100 VAC.

    Thus, this sort of approach isn't recommended unless you really need the high capacity - testing of other microwave ovens or ion laser power supplies, for example!

    A pair of these trnasformers can be connected in a similar manner to the tube-type TV power transformers described in the section: Typical Homemade Isolation Transformer, there are a few more things to keep in mind:

    A better way to use these is to take the primary (low voltage) windings from two similar transformers and mount them on a single core. Then, there is no high voltage to worry about, the unit is more compact and lighter in weight, and the performance is better (less voltage droop at high loads). Of course, disassembling the cores may prove interesting especially if they were originally welded!

    How Safe is a Homemade Isolation Transformer?

    Some people will claim that because it is homemade from salvaged parts, it *cannot* be as safe as a commercial unit.

    Keep in mind that I am not talking about using something that has been rusting away in a damp basement for 20 years. The power transformers from tube-type TVs or audio amplifiers must have been designed with isolation requirements in mind to obtain regulatory approval in the first place since they are used in equipment where the user may come in contact with metal parts.

    Also, the use of an isolation transformer is no excuse to ignore the other aspects of safe troubleshooting.

    It is easy to test for AC and DC leakage - and this should be done - to be sure that your transformers are in good condition. With two transformers, the probability of a failure is even smaller - 1/(P*P). Personally, I would trust the homemade transformer over a cheap import any day!

    Variable Autotransformers

    A variable autotransformer (Variac is the trade-name of one popular brand) enable the AC input to an appliance or piece of electronic equipment to be easily varied from 0 to full (or greater than full) line voltage. Your first Variac doesn't need to be large - a 2 A unit mounted with a switch, outlet and fuse will suffice for most tasks. However, a 5 amp or larger Variac is desirable. If you will be troubleshooting 220 VAC equipment in the US, there are Variacs that will output 0 to 240 VAC from a 115 VAC line. WARNING: A Variac is NOT an isolation transformer!

    The internal wiring of a typical Variac is shown below:

    
                     _                1 
              H o---- _-----/ ------>o--+     Tap 1: 0 to 115 VAC
                   Fuse 1  Power      2  )||
                  (Input)  Switch    o--+ ||  Tap 2: 0 to 140 VAC
                                         )||
                                         )||      _
          Tied together at               )<------- _--------o Adjustable output
          service panel           Power  )||     Fuse 2
          |              220       LED   )||    (Output)
          |          +--/\/\--|>|--|>|--+ ||
          |          |                   )||
          +-> N o----+------------------+-|-----------------o Return
          |                               |
          +-> G o-------------------------+-----------------o Ground
    
    
    WARNING: Direct connection between input and output - no isolation since the power line Neutral and Ground are tied together at the main service panel (fuse or circuit breaker box)!

    CAUTION: Keep any large transformer of this type well away from your monitor or TV. The magnetic field it produces may cause the picture to wiggle or the colors to become messed up - and you to think there is an additional problem!

    Note: the 'Power LED' circuit is soldered directly to a winding location determined to produce about 6 VAC.

    Wiring a Variable Autotransformer

    Typical variable autotransformers (e.g., Variacs) may be wired so that either clockwise or counterclockwise shaft rotation increases the output and for either 0 to 115 VAC or 0 to 140 VAC from a 115 VAC line (0 to 230 VAC or 0 to 280 VAC for units designed to operate on a 230 VAC line). There are also some Variacs that can produce 0 to 280 VAC from a 115 VAC line with the proper wiring (but they must have been designed for this!). Intermediate taps on the winding provide these options. The one for the LED, I add myself. :)

    Wiring is straightforward if you have acquired a bare unit (the following assumes a 115 VAC line, the extension to 230 VAC should be obvious):

    Variable Isolation Transformers

    This should probably be your basic setup for troubleshooting. You don't need to buy a fancy combination unit. A Variac can be followed by a normal isolation transformer. (The opposite order also works. There may be some subtle differences in load capacity.)

    Variac/Isolation Transformer with Current Limiting

    For the well equipped troubleshooter, there are also devices (Variacs and/or isolation transformers or combos) with adjustable (electronic) current limiting. This is particularly useful to protect the equipment being tested from excessive current - somewhat like the series light bulb but easily settable for each particular situation.

    Constant Voltage Ferrorsonant Transformer

    These provide very good line voltage regulation (typically +/-1% output change for a +10/-20% input change) without any active components. They also are very effective at suppressing line noise, spikes, and harmonics. SOLA is probably the most widely known manufacturer of these devices. A complete FAQ can be found at Sola Technical Support.

    Note that while isolation may be provided, it is NOT inherent in this technology. Some types may use autotransformers and thus have no isolation.

    (From: Dave Martindale (davem@cs.ubc.ca).)

    The simplest version has fairly ordinary-looking primary and secondary windings wound on the centre leg of a shell-type transformer core. Unlike a normal transformer, where the primary is wound over the secondary (or vise versa), the primary and secondary windings are physically separated. Magnetic shunts (chunks of transformer steel) are inserted between the centre and outside legs of the core at a point between the primary and secondary winding. These magnetic shunts provide a flux path around the primary that bypasses the secondary winding, producing lots of leakage inductance. This is what limits the current when the secondary is shorted.

    Meanwhile, the secondary winding is in parallel with a capacitor, chosen to make the secondary resonant at 60 Hz. The resonance drives the portion of the core inside the secondary winding into saturation, which limits the amplitude of the secondary voltage. Changes in primary voltage have almost no effect on secondary voltage over the regulating range.

    Now, the above is actually a simplification. In real CV transformers, the secondary actually has enough turns to step up the voltage by a factor of several, so the capacitor is operating at several times line voltage. This allows the capacitor to be lower capacitance for resonance, which is physically smaller and cheaper than what you'd need at 115 V. The actual output voltage is obtained from a tap on the secondary where the voltage is 115 V or so.

    Also, the transformer I've described so far outputs a pretty square waveform. That's great for the input stage of a DC power supply, but not for some AC loads. The commercial CV transformers I see use a "harmonic neutralized" design that gives an output closer to a sine wave. Instead of one secondary winding, there are two, with another pair of magnetic shunts between the two secondaries. The capacitor is connected across the two secondary windings in series. The output voltage is taken from just the "middle" secondary winding. In the Sola transformer, there's also an air gap in the centre leg of the core, at the end where the 3rd winding is. I don't understand how the extra winding and shunt cancel some of the 3rd harmonic output, but they do.

    The Series Light Bulb Trick

    When powering up a TV (or any other modern electronic devices with expensive power semiconductors) that has had work done on any power circuits, it is desirable to minimize the chance of blowing your newly installed parts should there still be a fault. There are two ways of doing this: use of a Variac to bring up the AC line voltage gradually and the use of a series load to limit current to power semiconductors.

    Actually using a series load - a light bulb is just a readily available cheap load - is better than a Variac (well both might be better still) since it will limit current to (hopefully) non-destructive levels.

    What you want to do is limit current to the critical parts - usually the horizontal output transistor (HOT). Most of the time you will get away with putting it in series with the AC line. However, sometimes, putting a light bulb directly in the B+ circuit will be needed to provide adequate protection. In that location, it will limit the current to the HOT from the main filter capacitors of line connected power supplies. This may also be required with some switchmode power supplies as they can still supply bursts of full (or excessive) current even if there is a light bulb in series with the AC line.

    Actually, an actual power resistor is probably better as its resistance is constant as opposed to a light bulb which will vary by 1:10 from cold to hot. The light bulb, however, provides a nice visual indication of the current drawn by the circuit under test. For example:

    Note: for a TV or monitor, it may be necessary (and desirable) to unplug the degauss coil as this represents a heavy initial load which may prevent the unit from starting up with the light bulb in the circuit.

    The following are suggested starting wattages:

    A 50/100/150 W (or similar) 3-way bulb in an appropriate socket comes in handy for this but mark the switch so that you know which setting is which! Or, for the ultimate in troubleshooting convenience, see the section: Combination Variable Isolation Transformer and Series Light Bulb Unit.

    Depending on the power rating of the equipment, these wattages may need to be increased. However, start low. If the bulb lights at full brightness, you know there is still a major fault. If it flickers or the TV (or other device) does not quite come fully up, then it should be safe to go to a larger bulb. Resist the temptation to immediately remove the series light bulb totally from the circuit at this point - I have been screwed by doing this. Try a larger one first. The behavior should improve. If it does not, there is still a fault present.

    Note that some TVs and monitors simply will not power up at all with any kind of series load - at least not with one small enough (in terms of wattage) to provide any real protection. The microcontroller apparently senses the drop in voltage and shuts the unit down or continuously cycles power. Fortunately, these seem to be the exceptions.

    Combination Variable Isolation Transformer and Series Light Bulb Unit

    If you plan on doing a lot of electronics troubleshooting consider building a box which includes:

    Using a Light Dimmer or Similar Device as a Variac?

    The quick answer is: No, get a proper Variac!

    The behavior of a phase control device like a light dimmer depends critically on what sort of load it sees. If the dimmer sees mostly a resistive load, it will work reasonably well and survive. However, most electronic equipment doesn't fall into this category. If the dimmer is attempting to drive a piece of equipment with a lot of capacitance or inductance, at the very least it will behave strangely with the control range squashed to one end or the other, or the output voltage will change suddenly rather than smoothly. But more likely, it will self destruct and/or damage the equipment due to the strange waveform, which may result in a peak output voltage that approaches full line voltage even at relatively low settings. There's also usually a minimum load below which it won't do anything predictable. In short, get a proper Variac. You know my motto: "You can never have too many Variacs!". :) Surplus Variacs are readily available including on eBay.

    What About the Scope Ground?

    The following also applies to other AC line powered test equipment where one lead is connected to the case.

    In general, oscilloscopes SHOULD be earth grounded. The only time this is not the case is if you are attempting to measure signals in a line-connected device like many TVs and switching power supplies, and are not using an isolation transformer. However, this is a very dangerous setup and should be avoided if at all possible. With line-connected equipment, the return or ground reference is not at earth ground potential due to the bridge rectifier or voltage doubler often used in the power supply front-end.

    Without an isolation transformer, connecting the scope ground clip to the return will result in a short through the ground lead between the equipment and earth ground. There will be smoke and possibly blown components as well in the equipment being tested, and possibly in the scope as well. The key here is that neither output of a bridge rectifier (the most likely front end configuration in line-connected power supplies) is at Earth Ground potential. They both have a large AC component with respect to Earth ground. Consider:

    
                         D1
            H o-----+----|>|-------+---------+-----o DC+
                   ~|    D2        |+        |
          In from   +----|<|----+  |       +_|_
          AC line        D3     |  |      C ___
                    +----|>|----|--+       - |
                    |    D4     |            |
     ---+-o N o-----+----|<|----+------------+-----o DC-
        |          ~   Bridge       -
        +-o G o------------------------o Earth Ground (also connected to scope)
       _|_
      ///
    
    

    Hot (H) and Neutral (N) are tied together at the electrical service panel. Now think about what would happen if the scope test probe ground lead was connected to DC- without an isolation transformer. This would basically short out D4 and put D2 directly across the line (among other things). Not good. With an isolation transformer for the power supply, there will be no fireworks. However, an isolation transformer for the scope will not help unless it has an isolated ground, or the scope ground is disconnected.

    Disconnecting the scope from ground allows its case to float which will prevent the melt-down but is EXTREMELY DANGEROUS since the entire scope cabinet is effectively connected to the power line. You (or someone else not familiar with your foolishness) may casually touch or lean against the scope cabinet and be thrown across the room if it is a lucky day or worse. Don't do it! Invest in an isolation transformer. It is very cost effective insurance.

    No solution is perfectly safe as there will always be potentially lethal combinations of terminals inside high power or high voltage equipment, but the idea is to minimize risks. Using an isolation transformer for the equipment being serviced along with a battery powered scope or one with ground leads that are NOT directly connected to Earth Ground and its case is best.

    However, many, if not most scopes, tie the ground leads and case to Earth Ground.

    One test method that potentially eliminates the issue of the scope ground entirely is to use the A-B setting available on most 2 (or more) channel scopes. However, the isolation transformer is still desirable for safety, and may be needed eliminate the large (identical) voltage swing which would be present on both probes, possibly affecting the measurements since the common mode rejection of the vertical amplifiers in many scopes may not be very good.

    In the end, developing proper work habits like keeping one hand in your pocket when dealing with high voltage or line voltage, changing test setups only with power off, and confirming that large capacitors are discharged before touching anything, are at least as important as isolation transformers and other safety gear in minimizing risks.

    Basic Ancillary Equipment

    Various common items are useful for testing of the following consumer electronics and computer devices. These will normally be used before and during use of any actual test equipment. (Some of these were already listed under the heading of 'test equipment'). However, this is kind of inverted identifying what is needed for each type of equipment being repaired.

    Incredibly Handy Widgets(tm)

    These are the little gadgets and homemade testers that are useful for many repair situations. Some of these can also be purchased if you are the lazy type. Here are just a few of the most basic:

    Cheater Cords

    In the good old days, before VCRs, before most solid state TVs, before the Net, and before newsgroups, most electronic equipment had a sort of interlock to prevent operation when the cover was removed. Normally this consisted of the line cord plugging into the chassis via a plug fixed to the cover. Then, emoving the cover automatically disconnected power to the equipment. So, a cheater cord was needed for testing and had an AC plug at one end and this special plug at the other to bypass the interlock and allow you to get a shocking experience. :)

    Exactly why this is no longer done except to save money isn't quite clear. Chassis of modern equipment like TVs, computer monitors, microwave ovens (especially microwave ovens) are very dangerous. Perhaps the manufacturers figure that at least for the first two, not using vacuum tubes, most of their voltages are lower. More likely, since they provide the warning "no user serviceable parts inside", they figure that they can't be sued and it is isn't worth spending the 10 cents for the extra plug. :)

    Where your equipment actually has this sort of interlock, it is usually possible to pop off a retaining clip and use the original cord for this purpose. Just make sure you understand the safety issues. Modern devices may not have several hundred volts sprinkled all over the chassis like those using vacuum tubes, but there may be non-isolated line voltage, 25 kV or more for the CRT, or 5,000 V at AMPs in a microwave oven. You can be just as dead from these!

    Monitoring Current Consumption from Batteries

    When a problem develops in a battery powered deviced - it might be totally dead or drain batteries too quickly - it is desirable to be able to measure the current from the batteries. A simple way to do this is to construct a gadget that can be inserted between two cells or between a cell and the battery holder terminal so that a multimeter can be installed in series with the battery output.

    (Portions from: Raydon Berry (rayberry@pt.lu).)

    Take a small piece of stiff plastic (e.g., as used in blister packs) and attach strips of self adhesive copper or aluminum foil to both sides. Shape one end of the strip into a sort of finger, narrow enough to slip between the AA or AAA batteries or batteries and the contact when they are installed in the holder. If the foil is copper, wires can be soldered to each side at the other end. If aluminum, cut away a portion of the foil in opposite locations on both sides so clip leads from a multimeter can be attached without shorting.

    This device is used (frequently by me) for checking the current consumption of all battery powered equipment - it's very simple and very cheap.

    For example, with remote controls, insert between batteries and put the multimeter on a range of about 25 mA and when you press each button, the code being sent will show up as a wagging needle on a VOM or an average current for a DMM. If the ceramic filter or the IR diodes have failed, the current remains very low, but if OK, you should see pulses of 5 to 10 mA.

    For other devices, select an appropriate range. It might not be a bad idea to check new/working equipment as well to obtain a "signature" of health which is recorded on a slip of paper glued inside the battery compartment. Then, if the device should fail, a comparison can easily be made.

    Miscellaneous

    Making a Bench Power Supply from a PC Power Supply

    The power supply from a long obsolete PC can be the basis for a low cost unit useful for a variety of design and troubleshooting applications. The typical 200 W PC power supply will provide +5 V at 20 A, +12 at 8 A, and low current -5 V and -12 V outputs. However, these are not that well filtered - at least not where low noise analog circuits are concerned. They are fine for digital and power circuits as is. For analog work, additional post regulation (e.g., LM317s) and filtering may be needed.



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    Soldering and Desoldering Equipment and Techniques

    Solder is Not Glue

    The ease and quality of your work will depend both on proper soldering as well as desoldering (often called rework) equipment.

    However, the purpose of solder is not to physically anchor connections - they must be mechanically secure first to assure reliability. When properly done, solder actually combines with the clean metal surface of the wires, pins, and terminals assuring a low resistance connection.

    While there are several conditions must be satisfied to achiev good reliable solder connections, with a little practice, soldering will become essentially automatic and you will know immediately when the results are satisfactory.

    There have been entire handbooks written on proper soldering technique. Organizations like NASA take this seriously - after all, a service call to the one of Jupiter's moons would be quite costly!

    Aditional information on soldering techniques and equipment can be found at:

    CAUTION: You can easily turn a simple repair (e.g., bad solder connections) into an expensive mess if you use inappropriate soldering equipment and/or lack the soldering skills to go along with it. If in doubt, find someone else to do the soldering or at least practice, practice, practice, soldering and desoldering on a junk unit first!

    Soldering Equipment

    Three wire grounded soldering equipment is recommended but I do not consider it essential for this type of repair work. However, a temperature regulated soldering station is a really nice piece of equipment if you can afford it or happen on a really good deal.

    I consider fine gauge rosin core solder (.030 or less) to be best for most applications (e.g., Ersin Multicore).

    A vacuum rework station is not needed unless you are removing your soldered in 500 pin Intel P6!

    Soldering Techniques

    Soldering is a skill that is handy to know for many types of construction and repair. For modern small appliances, it is less important than it once was as solderless connectors have virtually replaced solder for internal wiring.

    However, there are times where soldering is more convenient. Use of the proper technique is critical to reliability and safety. A good solder connection is not just a bunch of wires and terminals with solder dribbled over them. When done correctly, the solder actually bonds to the surface of the metal (usually copper) parts.

    Effective soldering is by no means difficult but some practice may be needed to perfect your technique.

    The following guidelines will assure reliable solder joints:

    Practice on some scrap wire and electronic parts. It should take you about 3 minutes to master the technique!

    Desoldering Techniques

    Occasionally, it will be necessary to remove solder - either excess or to replace wires or components. A variety of tools are available for this purpose. The one I recommend is a vacuum solder pump called 'SoldaPullet' (about $20). Cock the pump, heat the joint to be cleared, and press the trigger. Molten solder is sucked up into the barrel of the device leaving the terminal nearly free of solder. Then use a pair of needlenose pliers and a dental pick to gently free the wires or component.

    For stubborn joints or those connecting to the power planes (surface or multilayer boards), you may need to add some fresh solder and/or flux and then try again. Generally, if you only get part of the solder off the first time, repeated attempts will fail unless you add some fresh solder.

    Other approaches that may be used in place of or in addition to this: Solder Wick which is a copper braid that absorbs solder via capillary action; rubber bulb type solder pumps, and motor driven vacuum solder rework stations (pricey).

    (Portions from: Pat Brunner (Brunner@ieee.org).)

    I have used a SoldaPullet for 30 years but found an inexpensive improvement. Add a 1 inch length of silicone tubing (or something else that won't be damaged by the heat, 1/8" ID x 1/4"OD) over the SoldaPullet tip leaving 3/16" to 1/4" extending past the tip. This absorbs the downward force when the SoldaPullet is fired reducing damage to the PCB, provides a better seal around the component lead so it's often possible to clear a hole in one operation that might otherwise require several, and it prevents the plastic tip of the SoldaPullet from being damaged.

    Nick's Comments on Successful Desoldering Techniques

    These directly apply to the destructive (i.e., you don't care about saving the part) removal of IC chips. However, the basic techniques work for discrete parts as well.

    (From: Nicholas Bodley (nbodley@tiac.net).)

    A few points to keep in mind...

    Try to get cutters that will let you snip individual leads on the IC. Get tool catalogs! I like Contact East, in the USA; not sure about Canada. Jensen, in Arizona, I think, tends to be costly.

    If you snip all the leads on one side, you can bend the IC back and forth to break the other side free, but be sure to do the bending next to the plastic (it's harder to do there).

    When you cut the IC leads, do your best to leave most of each lead sticking up above the surface of the board.

    Set your iron to about 770 deg. F (400 deg. C). (This assumes a modern soldering station with a temperature control, and a relatively-slender tip.) Be sure that the tip is clean and shiny and properly tinned. Any oxidation is just no good. (DON'T file modern plated tips! You'll remove the plating!). Be fanatical about ensuring that the tip always idles with a decent coating of solder.

    Hotter temps run a real risk of spoiling the adhesive bond that holds the copper foil to the board. DO NOT use a higher temp to make up for an improperly-tinned tip!! (You might need a higher temp for holes in the middle of ground planes, however. These will sink the heat away effectively; but do those separately.)

    You must get each pad hot enough to be well above the melting point, so that the cold air won't make the solder resolidify when you slurp it up.

    To transfer enough heat, you must have a fillet of solder between the tip and the pad. If necessary, add a bit of solder to ensure this!

    After hitting these points so hard, I'll relax and say that you'll really do better if you remove each lead stub individually with assembly tweezers (AA style are good) or thin needle-nose pliers.

    Once they're all out, then you need to be concerned about heating the pads enough. Now you can desolder. The other messages in this post have good advice on that.

    You need to maintain your desoldering tool, too. It might not have good vacuum if ignored.

    It's tricky to hold the iron on the pad while getting the nozzle close enough, but a decent desoldering tool will work if tilted somewhat to let the tip contact the pad.

    If a hole doesn't open, but some solder has been slurped up, you could try good solder wick (Solder-Wick (Soder-Wik?) brand is good); it can sometimes pull up solder from underneath by capillary action. (I didn't believe this until it happened!) Poor solder wick isn't fluxed sufficiently, or might be subtly corroded. It should soak up solder like a sponge.

    It might be quicker to refill the hole with a bit of solder and repeat; there could be a good blob of it on the other side, which you might, or might not, be able to get to.

    (If you can get to both sides, and have five hands, you could apply heat to one side, let the tip dwell for a few seconds to melt all the solder, and slurp from the other side.)

    If things become messy, apply liquid flux (seems not to be too easy to find in small quantities; I use a flux pen, which seems not overpriced). Reheat the pad, and the flux should do a great job of tidying things up. It tends to let capillary action make the holes open wider, when most of the solder has been picked up.

    I think it's well worth the effort to cut the leads free from the IC body and remove them one at a time, then go over the pads a second time to remove the solder.

    I have very recently removed a 16-pin DIP twice from a location without damaging the pads at all by these principles.

    It's much harder, or impossible, to do good work with poor tools. Do try to get good tools, and learn to take care of them.

    Soldering Pins in Plastic Connectors

    The thermoplastic used to mold many common cheap connectors softens or melts at relatively low temperatures. This can result in the pins popping out or shifting position (even shorting) as you attempt to solder to them to replace a bad connection, for example.

    One approach that works in some cases is to use the mating socket to stabilize the pins so they remain in position as you solder. The plastic will still melt - not as much if you use an adequately sized iron since the socket will act as a heat sink - but will not move.

    An important consideration is using the proper soldering iron. In some cases, a larger iron is better - you get in and out more quickly without heating up everything in the neighborhood.

    Comments on Repairing Damage to Printed Circuit Boards

    Two common problems are discussed here: damaged traces and damage from overheated components.



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    Supplies and Parts

    Lubricants, Cleaning Agents, and Other Liquidy or Slimy Stuff

    Note that using no insulator is always better than one with heatsink compound for these materials (no data on BeO which may be the exception).

    (From: Gavin Parrish (the_big_geez@ameritech.net).)

    Kano Labs makes a number of exceptional products which are only available directly through them. They are not cheap, but all that I have tried have met or exceeded my expectations. Their premier product is "KROIL" a penetrating oil that breaches a space as small as one millionth inch. No fooling! Throw away that WD whatever-its-called stuff. If it's stuck, this will unstick it.

    While they have a lot of really big industrial customers, they give attentive service even if you only buy 1 can. The only drawback is they keep sending you somewhat amusing flyers every month or so. You already get a lot of this so it's no big deal.

    For info or ordering contact: (what? no URL?!): Kano Laboratories, 1000 Thompson Ln., Nashville, TN 37211-2627. Phone: 1-615-833-4101, Fax: 1-615-833-5790.

    (The above is not a paid promotion, merely data I hope you find useful.)

    (From: Rich Grise (richardgrise@yahoo.com).)

    Which solvent to use depends on what you're trying to dissolve. For a something like a cruddy motor, I'd try, in order from least aggressive up:

    1. Isopropyl alcohol - good on most oils and greases, fairly innocuous chemically.

    2. Ethyl alcohol - as good a solvent, or better than isopropyl, but much too valuable as a beverage.

    3. Methyl alcohol - don't even touch this crap - if you even just get it on bare skin, it can blind you. (Actually, this is an extreme position, methyl alcohol is mainly dangerous if ingested. --- Sam.)

    4. Naphtha (lighter fluid) - the only solvent I've ever seen that can get chewing gum out of your hair. Not too good on aliphatic greases, however.

    5. Mineral spirits or turpentine - still flammable, makes good paint thinner, but seems to leave a greasy residue when used for cleaning.

    6. Toluene/xylene - excellent cleaner, but it could attack the insulation on the windings. Breathing the fumes can cause a sort of intoxication that I think isn't very good for you.

    7. Acetone/MEK - MEK is less volatile, but still quite aggressive. Very flammable, but evaporates completely without residue. Acetone is the only thing I've ever seen that can dissolve acrylic plastics like Plexiglas.

    The chlorinated/fluorinated solvents sit somewhere in the middle of the range - someone else pointed out the difference between trichloroethylene and trichloroethane; I guess TCA is much friendlier than TCE - but we used them in the Airforce to clean up hydraulic fluids that nothing else would even touch.

    I've heard that Vaseline makes a superb lubricant for bike bearings; it also makes a reasonable vacuum seal, and it's incredibly tenacious - one day, I used it on a gasket, and when I needed to make a change, I couldn't find anything in the shop that would clean it up completely.

    Don't use WD-40 as a cleaner; it gums everything up. I inherited an old Baudot teletype once and thought I'd clean it with a WD-40 spray. HAH! Spent the next week disassembling the thing and cleaning all the gunk off the intricate little parts with TCA or something. WD-40 is good for door hinges.

    Carburetor cleaner is a mixture of solvents in a spray can which may include acetone, toluene and methanol but it's extremely flammable and it seems to wash greasy dirt away as if it weren't even there.

    Adhesives

    Electronic Sealers and Potting Compounds

    These may be needed to insulate a high voltage connection or to encapsulate a circuit for reliability (or to keep it from prying eyes!).

    Ordinary silicone window and bathtub caulk has the right mechanical and electrical properties (tough, flexible, excellent insulator especially for high voltage), but it secretes acetic acid upon curing and this may damage the electronic circuitry (but not always the case). Some types claim to be safe for this or that (e.g., aluminum) but unless it states specifically that it is safe for electronics, use at your own risk.

    (From: Ralph L. (ralphl@keycomp.net).)

    You can also use an RTV that is safe for oxygen sensors that are used on most computer controlled cars. It does not produce that acetic acid (vinegar smell) during the curing process and will not harm electronics.

    (From: Greg Szekeres (gjs@prophet.pharm.pitt.edu).)

    Yes, Permatex Ultra Blue is safe, available at most auto parts stores. I have also been using polyurethane instead of silicone, although is has problems with some materials.

    (From: RadMan (radcom@comnet.ca)).

    Some agents require UV to cure, some need heat. You can also try Miller-Stevensen 907 available at Future/Active, and it pots with a heat gun very fast (30 minutess).

    (From: Bob Wilson (rfwilson@intergate.bc.ca).)

    Dexter makes Hysol Epoxy which is a potting compound that totally encapsulates the circuits. There are easily available commercial coloring compounds intended for this purpose, and are available from the supplier of the Epoxy. An alternative is to mix some laser copier toner (dry powder) with the epoxy if making it opaque is desired.

    Mind you, all that potting does as a means of security, is to keep he amateurs out. Depotting an electronic assembly is pretty easy. All that is needed is judicious application of a small welding torch flame to locally heat the epoxy above its glass temperature (whereupon it becomes rather "crunchy" and easy to remove), and a little patience.

    (From: Brian Symons (brians@mackay.net.au).)

    The products normally safe to use are labeled "neutral cure" or at least they are here in Australia.

    Any acid cure product is certainly dangerous around electronics. I cam across some PCB's that had had the wires glued in place by a run of acid cure silastic across the board.

    When looking for the fault, I peeled up the silastic and found every track under the silastic was completely eaten away.

    BTW. Over here, It is quite common for ovens to have a from glass viewing window that is glued in position with a silastic material that can handle the high temps.

    When a warrantee guy ordered in a tube of the silastic, they supplied a tube of the silastic that is available here at car parts suppliers and service stations to repair windscreen seals. They were only charging about eight times the price though. This silastic is a black product. I have used it successfully for oven glass repairs for several years.

    Electronic Parts

    I was going to attempt to make a basic list of recommended parts but this quickly got out of hand. The list below is just a start. The idea is to have enough parts available so that you do not need to raid the local electronics store every time you want to try something.

    A good source for many of the basic parts is dead equipment - their organs can live on at your workbench. Parts like small resistors are so inexpensive that this doesn't warrant a lot of time. However, power resistors, potentiometers, power semiconductors, some ICs, etc. are well worth saving. Used electrolytic capacitors will generally still be functional but these do deteriorate with time and heat so testing them first and avoiding the use of really old ones for the permanent repair is probably wise. The majority of my parts inventory is from salvage. Think of them as 'pre-owned burned in components' :-).

    Mechanical Parts

    Plastic Parts Repair

    When a little plastic part breaks, repair can be a time consuming, frustrating, and ultimately futile task unless the failure was from abuse. The reason is that when a part breaks under normal operating conditions, the plastic gives way at the areas of maximum stress. Simply gluing the part won't work because the strength after the repair will probably not be as great as it was originally even if the proper adhesive is used.

    Note that there are quite a variety of what we call "plastics". An adhesive that bonds with extreme strength to one may not even stick at all to another. (Nylon and polyethylene are difficult to glue; styrene is easy.) This is especially true of the 'welding' adhesives like MEK.

    However, using the most appropriate glue can make a very significant difference:

    WARNING: The vapors from all of these adhesives are harmful to health if inhaled. Work only in a well ventilated area.

    CAUTION: Spills from some of these will also damage paint and other plastic surfaces (including eyegless lenses!) even if wiped up immediately.

    Where possible, I add reinforcement to plastic parts - either with plastic or metal. Or, fabricate all metal replacements. I've heard of people successfully adding bits of metal to replace plastic gear teeth. I have several clock radios with a mechanical clock where the little plastic pin in the number changing mechanism invariably broke after 5 years or so on all similar models. I replace them with a piece of steel wire (from a large paper clip) glued in place. This repair has worked for over 20 years. I bet the manufacturer saved a fraction of cent on each unit though! And, when someone forebly removed a paper jam on an HP DJ1000 printer and broke several pressure roller spring levers, stiff steel wire came to the rescue once again.



  • Back to Troubleshooting Table of Contents.

    Sources of Information and General Comments

    This set of sections deals with ways of locating general electronics repair information as well as problem specific specifications, datasheets, manuals, and tech-tips. Since we first presented this set of topics several years ago, there have been two major trends which are worth noting, one good, one bad:

    References

    Each of the repair guides in the "Notes on the Troubleshooting and Repair of" series includes a list of relevant links and books on the technology and servicing. Also check out:

    Manufacturer's Service Literature

    Service manuals are still available for a great deal of consumer electronics. Once you have exhausted the obvious possibilities or mechanical problems, the cost may be well worth it. Depending on the type of equipment, these can range in price from $10 to 50 or more. Some are more useful than others. However, not all include the schematics so if you are hoping to repair an electronic problem try to check before buying.

    Identifying OEM Manufacturer - FCC Numbers

    Only a few manufacturers actually produce the vast majority of consumer electronic equipment. For example, Radio Shack, Magnavox, and Emerson do not make their own VCRs (I can tell you are not really surprised!). House brands are nearly always the products of well known manufacturers identical or very nearly identical to their standard models but repackaged or at least relabeled to reflect the store chain's name and logo. This is one reason why such lower cost products may be a good deal (but not always).

    How do you determine the actual manufacturer? For most types of consumer electronic equipment, there is something called an 'FCC ID' or 'FCC number'. Any type of equipment that may produce RF interference or be affected by this is required to be registered with the FCC. This number can be used to identify the actual manufacturer of the equipment.

    A cross reference and other links can be found at:

    Sams' Photofacts

    Sams' (no relation) is Sams Technical Publishing (formerly Howard Sams & Company) who publishes circuit diagrams and service info for just about every TV sold on this planet since the 1940s.

    Sams' Photofacts schematics and service literature are published by:

    You can search the Web site to determine if they have a folder for your model. Service info (EFacts) for most models manufactured after 1992 is available in electronic form (currently) about $11. These are similar to the print PhotoFacts but may be ordered on-line and will arrive via email within 1 business day.

    These folders of service information have been published for over 45 years (I don't know for how long but I have a set for a 1949 portable 3 inch Pilot TV - about as portable as an office typewriter if you remember what one of those was like) and are generally the best most consistent source of service info for TVs, radios, some VCRs and other consumer electronics. There are some Computerfacts but the number of these is very limited. The VCRfacts are also somewhat limited and the newer ones tend to have strictly mechanical information.

    Even if they don't list your model, they may have a folder for one using the same chassis so search by chassis number as well. Even if this doesn't help, there still may be a folder for models that are similar enough to be of value (though you really have to be in the library to be able to determine this by looking at the circuit diagrams or photos) so check out folders for other model numbers that are close to the one you really want.

    Sams' Photofacts are often available (for photocopy costs) from you local large public library which may subscribe to the complete series. If not, a large electronic distributor can order the selected folder for you.

    One advantage of the Sams' info is that it is compiled in a very consistent format so that once you are familiar with one model TV, it is easy to transfer that knowledge to any other. They provide waveforms at key locations and DC voltage measurements almost everywhere. Additional info such as IC pin to ground and coil resistances are often provided as well. The manufacturer's service manuals are generally not nearly as complete.

    Note: I have heard that some of the Photofacts recently purchased directly from Sams Technical Publishing/Howard Sams have been poor photocopies with illegible scope waveforms rather than original printings. If this is the case, it is truly the end of an era and too bad. In any case, try to confirm the quality before you buy or get your info from the library.

    Inside Cover of the Equipment

    Television sets and even old radio often have some kind of circuit diagram pasted inside the back cover. In the old days, this was a complete schematic. Now, if one exists at all, it just shows part numbers and location for key components, occasionally some test points and voltages - still very useful. Some TVs - as late as 10 years ago, maybe even now - included a complete schematic with the product information and owner's manual. I have a 1984 Mitsubishi which came with a very nice high quality multi-page schematic. However, this is the very occasional exception rather than the rule anymore for A/V equipment.

    Microwave ovens do almost always have a schematic diagram of the microwave power generation circuitry pasted inside the sheetmetal cover. This will generally include at least the high voltage transformer, interlocks, rectifier, capacitor, and magnetron. Since most microwave oven problems are in these areas, this is all you are likely to need. The controller, especially electronic units, is often omitted or only covered superficially.

    Additional Sources for Service Information and Manuals

    Where service information on your equipment isn't available as a Sams' Photofact (or even if it is), NAP is another possibility. They aren't that expensive, Maybe $25 for a set of 6 microfiches (well, you can't have everything!) that covers a variety of models including the one you are specifically interested. NAP's phone number for parts is 1-800-851-8885. They will look up your model in their database and identify the microfiche set(s).

    There are now many many Internet sources for manuals and schematics of all types including those that are hard-to-find for vintage equipment. Some are free while others charge anywhere from a nominal fee to something ridiculous. Do your homework before spending money - most of those you likely need may be downloaded for free including those for major brands of test equipment, communications gear, and tube audio.

    The links that used to be below have been removed since attempting to maintain two sets of nearly identical links (here and in my bookmark file), many with short half-lives, became unbearable. Therefore, please go to the "Manuals/Schematics" sections of Sam's Neat, Nifty, and Handy Bookmarks.

    As of Fall, 2006, I have confirmed that all these Web sites for manuals and schematics are active. Note that since these sorts of sites come and go, I'd advise downloading and archiving whatever you might possibly need when you find them - don't just save the links. You may be sorry later!

    (From: William E. Miller (eagle@trader.com).)

    Besides the used Sams TV Repair Manuals I sell, here are a few good sources for various flavors of service manuals.

    The U.S. Military has an extensive library of test equipment and related manuals, some of which are in the public domain:

    (From: Dino (kl0s@cox.net).)

    Go to: U.S. Army Logistics Support Activity. Select "Publications and Forms" which should get you to LOGSA Publications and Forums. Then select "Electronic Technical Manuals Online" which will roll you down to "Go to Electronic Technical Manuals Online". Click on this link which takes you to http://www.logsa.army.mil/etms/online.htm. If you accept their terms, click on "I accept" which takes you to http://www.logsa.army.mil/etms/welcom1.htm Choose "Enter the Site" [Note the disclaimer that you have to login if accessing anything but public release manuals and that you have to have 128 bit encryption engaged. That should bring you to: http://www.logsa.army.mil/etms/find_etm.cfm. which is the search page; click on "TM Title Text" and enter, for example, "Tektronix" and scroll down to hit "Search" which should get you to: http://www.logsa.army.mil/etms/show_etm.cfm where if you scroll down and look CAREFULLY you'll find lots of material in .PDF format which you can then download.

    You may have to go through this entire process to establish the fact that you accept their terms. There's probably a cookie in my system that lets me go straight to the search page. I've found a number of good references here for text equipment.

    Canadian Schematics Source

    This outfit seems to have schematics for a variety of old or vintage TVs, radios, car radios, CBs, amplifiers, and more.

    (I have updated the contact information below so am not sure if everything applies to the new distributor. --- Sam.)

    (From: John R. Hepburn (jhepburn@recorder.ca).)

    I use a source in Canada for cheap schematics. I have to mention that they have limited coverage in the last while due to some O.E.M. holdbacks. There is nothing at all on monitors. It is:

    What they do cover is inexpensive, typically 5 schematics + data in one $19.50 manual ($14.00 U.S.). An example, I just received a manual the other day that I ordered to service a Sony VCR. It contained the following.

    1. Citizen TV model JCTV-0204/JCTV-3097
    2. Citizen VCR model JVHS-3931
    3. Hitachi TV model CY07 C#G9LXU1M
    4. Hitachi VCR model VT-M262A
    5. Sony VCR models SLV-340/380/440/441

    I suggest ordering their master index. They have 2 of them, pre-1973 and 1973 to present. You will need it for crossing anyway and it will give you a better idea what value their resources will be to you. Cost for an index is $5.00 (Can).

    Reverse Engineered Schematics

    A number of companies are in the business of generating schematics either from samples of the equipment or by 'other means' (which we won't go into). One such company that claims to have over 3,000 such schematics is:

    I have no idea of their cost, reliability, quality, or accuracy but this type of source may be worth checking if you are desperate! One risk is that he wants $5 for catalogs of at most 3 categories from the following before you can order: audio, auto/air/marine, computer, detection, industrial, lighting, medical, phone, power supplies, radar, radio, security, tape/disk, telemetry, television, test equipment, time, toys & games, video, potpourri (misc).

    Here is another company which has some reverse engineered schematics:

    They have some PS/2 and other PC and monitor related schematics but not nearly the selections it would seem as Bomarc, above. I do not know anything more about this company.

    Reverse Engineering Your Own Schematics

    Of course, most of us have had need to reverse engineer equipment. This is probably not realistic for a multilayer PC mainboard. But for even something as complex as a TV or computer monitor, it may not be that difficult - and in some cases, the only option. I generally do this by going component by component and determining all connections to each one. The initial drawing will be a total mess - a spaghetti diagram. :) Once the wiring has been determined, I redraw the circuit (you've seen enough of them in these pages!). Everyone who does this more than once probably has their favorite technique to make the task easier.

    (From: Jeff Zurkow (jeff@atrox.com).)

    Here's a trick I'm using for reverse engineering: Put the board on a color photocopier, set the copier for "mirror image", and make a copy. This gets you a top view of the underside, as if the board were transparent. You can tape a piece of drafting mylar over the copy, and draw in the topside components and traces with colored pencils. In fact, I sometimes use multiple mylars: top traces on one, components on another, component values on a third, and a final one on which I check off components and solder joints as I draw them on the schematic. It helps to have a light box :)

    The layered drawing can also serve as a component-location key for future troubleshooting. Just assign new component identifiers (the ones silk-screened on the board are often obscured by the components), and draw them in on both the mylar and the schematic. Makes it real easy go from the schematic back to the circuit board.

    Mark's Approach to Finding Information

    The first skill you need when you want to design something is digging up the databooks. This applies to troubleshooting and repair as well. A well stocked literature shelf (f cabinet) is an invaluable time saver. Don't assume you can get EVERYTHING on the net just yet!

    Take the lowly 2N3055 power transistor, for example.... (Most of us have its specs engraved on some radiation-hardened neurons safely tucked away in a forgotten part of our brains but for the freshly minted EE or technician....

    (From: Mark Zenier (mzenier@netcom.com).)

    Places to look:

    The web, at sites for companies that make power transistors. A whole bunch of people make jelly bean transistors like 2N3055s, down to some little 50 employee companies that you've never heard of, but they may not have a web site yet). Or start with one of the web directories. (Check the "Electronic Components" sections of Sam's Neat, Nifty, and Handy Bookmarks.)

    The sales rep, sales office, or company literature department. Look in the phone book or on the web page for the phone number of a company or their local or regional sale representative or office. Call them up and ask. It's their job to provide customer support and if you sound like you halfway know what you're doing (saying you're a student works, too) AND it doesn't cost them much (don't get greedy) they'll often be more than willing to send you information. (These days, it might be a CD-ROM of their whole product line. Cheap, but not that easy to use, IMHO.) If they won't help you, ask them where there is someone who can. Like the nearest distributor.

    Electronics distributors. Larger ones often fill the same literature distribution role as the sales rep. Other distributors like Jameco, JDR Microdevices, Future Active sell databooks as a catalog item. Or a local distributor that caters to the walk in trade will have a databook shelf and allow (or have a nominal fee for) photocopies. (The big distributors are closed operations, mostly using phone salesmen and UPS for distribution, visitors aren't necessarily welcome.)

    A good library. Like one at a university with an electrical engineering program, or a large city library.

    Used book stores, a big unselective 'book dump' often will have a good stock of old databooks. Ones that you can't get from the manufacturer and more. Likewise, electronics surplus stores (most big cities should still have one or two) often have them.

    Parts Information and Cross References

    I have found that one of the most useful single sources for information on semiconductors, especially for troubleshooting and repair, to be the ECG Semiconductors Master Replacement Guide. (ECG is now merged with NTE.) It used to be about $6 and may possibly be available for download free now from the NTE Web site (but it's huge). SK and others have similar manuals but NTE, especially with its acquisition of ECG, now appears to dominate the industry. The manual will enable you to look up U.S., foreign, and many manufacturer's 'house' numbers to identify device type, pinout, and other specifications.

    Also see the section: House Numbers.

    Here is the current Web site for NTE:

    (From: Gregg (gregglns@ix.netcom.com).)

    "NTE's device numbers are the same as ECG's, and their cross-ref guide can be downloaded from http://www.nteinc.com/.

    It's free but they do want you to register. If you want to bypass this, go to ftp://nteinc.com/pub/ and download the windows version of the guide, ntesetup.exe. Don't bother with the dos version; the file named dosdisk2.exe is bad, and won't unzip."

    I am not necessarily recommending using NTE (or other generic) replacements if the original replacements are (1) readily available and (2) reasonably priced. (Note that very often the original replacement part will be less expensive than the equivalent from NTE. Therefore, it should be used if available.) However, the cross reference can save countless hours searching through databooks, seaching the Web, or contacting the manufacturers. Even if you have a wall of databooks, this source is invaluable. However, there are a couple of caveats:

    1. Some crosses have been known to be incorrect - the specifications of the generic replacement part were inferior to the original or totally wrong with different pinout or even function!

    2. Don't assume that the specifications provided for the generic part are identical to the original. Since a single NTE part may replace multiple standard parts, it may actually be better in some ways. Thus, using one of these cross references to determine the specifications of the parts in your junk bin can be risky.

    I often use the replacement guide to determine upper bound specs but as noted above, rarely buy any generic parts (sorry NTE). Then I find industry standard parts that have equal or better specs. Dalbani's catalog (see the section: Mail Order Parts Sources) has a sort of inverse cross-reference from NTE to 2S/2N/BU/whatever that isn't a bad starting point (though probably not to be trusted without confirmation of actual specs). Of course, this doesn't necessarily help with some tricky HOTs and choppers....

    Note that while Howard Sams of Sams' Photofact fame publishes a semiconductor cross reference manual (or used to), it would appear to just be a compilation of the ECG, NTE, SK, and Radio Shack manuals - and much more expensive ($25 or so).

    For standard ICs, IC Master used to be the "bible" for IC references. It can often provide quick access to complete data. Full access to their Web site is currently free but they do require registration. However, with their print version, ICs no longer manufactured were not listed. I assume the on-line version will be similar. Thus, it may be of only limited value for older equipment.

    DigChip is one of a growing number of on-line services that provide cross reference and manufacturer links. Many like this one are free but require simple registration.

    There are also specifications and/or datasheets for many Japanese semiconductors as well as ICs and other parts at Roy J. Tellason's Parts Pages.

    Transistor Designations

    Unfortunately, there is no such thing as a universal part number! Aside from the VERY expensive D.A.T.A. semiconductor reference series (don't even ask), which includes virtually all types and flavors of devices, there are various Japanese Semiconductor Reference manuals available through places like MCM Electronics for around $20. Some of the text may be in Japanese but the relevant data is in English so these are handy if you want more detailed or precise specifications for these devices than provided by cross references such as NTE.

    More on Transistor Designations

    A common labeling scheme for MOSFETs consists of a 2 digit number followed by "N" or "P" followed by another 2 digit number: II T VV. This may be embedded in a much longer part number.

    (From: Mark Robinson (mark-r@snow_white.ee.man.ac.uk).)

    We are lucky with transistors that, apart from a few oddities which I'll talk about later, most markings follow one of these codes. ICs are more tricky as you're often dealing with custom chips or mask programmed devices with manufacturers individual codes. A quick hint though: always look for known numbers (e.g., 723, 6502, 2764) etc. between the suffix and prefix, and beware of the date code.

    Right... Back to transistors. The three standard transistor marking schemes are:

    1. Joint Electron Device Engineering Council (JEDEC).

      These take the form:

          Digit, letter, serial number, [suffix]

      where the letter is always 'N'.

      The first digit is one less than the number of legs, (2 for transistors unless they're crippled although I'm not sure about 4 legged transistors maybe they get a 3) except for 4N and 5N which are reserved for optocouplers.

      The serial number runs from 100 to 9999 and tell nothing about the transistor except its approximate time of introduction.

      The (optional) suffix indicates the gain (hfe) group of the device:

          A = low gain
          B = medium gain
          C = high gain
          No suffix = ungrouped (any gain)

      See the data sheet for the actual gain spread and groupings. The reason for gain grouping is that the low gain devices are fractionally cheaper than the high gain devices, resulting in savings for high volume users.

      Examples: 2N3819, 2N2221A, 2N904.

    2. Japanese Industrial Standard (JIS).

      These take the form:

          Digit, two letters, serial number, [suffix]

      Again, the digit is one less than the number of legs.

      The letters indicate the application area and flavour of the device according to the following code:

        SA: PNP HF transistor
        SB: PNP AF transistor
        SC: NPN HF transistor
        SD: NPN AF transistor
        SE: Diodes
        SF: Thyristors
        SG: Gunn devices
        SH: Unijunction transistor
        SJ: P-channel FET/MOSFET
        SK: N-channel FET/MOSFET
        SM: Triac
        SQ: LED
        SR: Rectifier
        SS: Signal diodes
        ST: Avalanche diodes
        SV: Varicaps
        SZ: Zener diodes

      The serial number runs from 10 to 9999.

      The (optional) suffix indicates that the type is approved for use by various Japanese organizations.

      NOTE. since the code for transistors always begins with 2S, it is sometimes (more often than not is seems) omitted so, for example, a 2SC733 would be marked C733.

      Examples: 2SA1187, 2SB646, 2SC733.

    3. Pro-Electron.

      These take the form:

          Two letters, [letter], serial number, [suffix]

      The first letter indicates the material:

        A = Ge
        B = Si
        C = GaAs
        R = compound materials

      Needless to say the biggest majority of transistors begin with a B.

      The second letter indicates the device application:

        A: Diode RF
        B: Variac
        C: Transistor, AF, small signal
        D: Transistor, AF, power
        E: Tunnel diode
        F: transistor, HF, small signal
        K: Hall effect device
        L: Transistor, HF, power
        N: Optocoupler
        P: Radiation sensitive device
        Q: Radiation producing device
        R: Thyristor, Low power
        T: Thyristor, Power
        U: Transistor, power, switching
        Y: Rectifier
        Z: Zener, or voltage regulator diode

      The third letter indicates that the device is intended for industrial or professional rather than commercial applications. It is usually a W,X,Y or Z.

      The serial number runs from 100-9999.

      The suffix indicates the gain grouping, as for JEDEC.

      Examples: BC108A, BAW68, BF239, BFY51.

      Apart from JEDEC, JIS and Pro-electron, manufacturers often introduce their own types, for commercial reasons (ie to get their name into the code) or to emphasize that the range belongs to a specialist application.

      Some common brand specific prefixes are:

        MJ: Motorola power, metal case
        MJE: Motorola power, plastic case
        MPS: Motorola low power, plastic case
        MRF: Motorola HF, VHF and microwave transistor
        RCA: RCA
        RCS: RCS
        TIP: Texas Instruments power transistor (plastic case)
        TIPL: TI planar power transistor
        TIS: TI small signal transistor (plastic case)
        ZT: Ferranti
        ZTX: Ferranti

      Examples: ZTX302, TIP31A, MJE3055, TIS43.

      Many manufacturers also make custom parts for large volume OEM use. These parts are optimized for use in a given part of a given circuit. They usually just have a manufacturers stamp and an untraceable number. Often when a company goes bankrupt, or has surplus at the end of a production run, these transistors find their way into hobbyist bargain packs. There is no way that you can trace data on these devices, so they are only suitable as LED drivers, buffers, etc, where the actual parameters are not important. Check carefully before buying.

    Once you have identified your part, a trip to the data sheet or equivalents book is called for (anyone know of an on-line equivalents list?).

    Surface Mount Parts

    Due to their small size, very little information is printed on the actual package for diodes, transistors, capacitors, and other discrete devices.

    House Numbers

    These are the cryptic numbering like 121-1025 or 113234 that may be the only marking on that critical part you need to replace or identify.

    Are house numbers used just to make life difficult?

    It certainly seems that way from the perspective of repair. Give me industry standard numbers anyday. However, house numbers are a fact of life.

    The house number is what you need to order a replacement from the original manufacturer of the equipment but that may not always be desirable due to the likely high cost and possible difficulty in locating a suitable distributor that carries the manufacturer's replacement parts.

    As noted in the section: "Parts information and cross references", a Master Selection Guide like NTE may be able to give you some idea of the specifications even if you don't want to use their generic replacement semiconductors. Their web sites have (or should have in the future) some amount of cross reference information for industry standard and house numbers. However, don't expect to detailed IC specifications or even pinouts in most cases there or from the disks they may also offer. The hard-copy Master Selection Guides which these companies sell have been better in the past (though this may be changing) but even these won't give you all the details. However, if you do repair work regularly, these 'telephone book' thickness guides worth the few bucks that is charged.

    Also see the section: Parts Information and Cross References.

    Generic Parts (Mostly Semiconductors)

    NTE (which now includes ECG) offers an extensive selection of discrete devices and integrated circuits which are replacements for thousands of industry standard as well an house numbered semiconductors. Should you consider them? My general feeling is: not unless you have to. They are often more expensive than the parts they replace and quality is not always quite as high as an original standard part. However, in most cases, these parts will work just fine.

    Other common components including flyback transformers, belts and other rubber parts, and RF modulators may also be available from these sources but they tend to be used less often and quality may vary even more.

    There are some other similar companies like SK (part of Thomson Consumer Electronics) but NTE now appears to dominate the industry for these generic replacement semiconductor and other electronics components.

    HP-to-Industry Standard Semiconductor Cross Reference

    (From: Walter Shawlee 2 (walter2@sphere.bc.ca).)

    Sphere's Used Electronic Test Equipments will help decode all those odd 1820-xxx numbers! Also HP and Tek repair parts and equipment on line, plus helpful FAQs and links to all kinds of test gear sites.

    We also have a big used equipment site on line for Canadians.

    Internet Sources of Information

    Most manufacturers of electronic equipment are now providing info via the World Wide Web. The answer to you question may be a mouse click away. Perform a net search or just try to guess the manufacturer's home page address. The most obvious is often correct. It will usually be of the form "http://www.xxx.com" where xxx is the manufacturers' name, abbreviation, or acronym. For example, Hewlett Packard is hp, Sun Microsystems is sun, Western Digital Corp. is wdc. It is amazing what is appearing freely accessible via the WWW. For example, disk drive manufacturers often have product information including detailed specifications as well as complete jumper and switch settings for all current and older harddrives.

    Tandy (Radio Shack) used to have a nice web resource and fax-back service. This was mostly for their equipment but some of it applied to other brands and there were diagrams that were useful for other manufacturers' VCRs, TVs, CD players, camcorders, remote controls, and other devices. However, the page is long gone and no realy useful info is obvious on Tandy's Web site.

    Are There Schematics of Consumer Electronic Equipment on the Web?

    Well, yes and no.

    You are searching for the Holy Grail. Everyone is, but it isn't going to happen on a large scale - at least not for free. Schematics are copyrighted by the equipment manufacturers who sell them as part of their service manuals or license them to organizations like Sams Technical Publishing (Sams' Photofacts) and others.

    That is my take, at least.

    Having said that, there are many Web sites with schematics that may or may not have been legally copied and made publicly available. See the section: Additional Sources for Service Information and Manuals.

    Taking the Unit to a Repair Shop

    As with medical problems, an accurate diagnosis can only be made with good complete information. Use your senses to their fullest. If you do decide to have the unit professionally repaired - and depending on your level of experience and confidence, this may be the wisest choice - the more complete your description of the problem the easier (and cheaper) it will be to locate the problem. Include functional behavior or lack thereof, mechanical and electronic sounds it makes, anything that is related at all to the operation of the unit. Sometimes seemingly unrelated factors can be important. For example, the fact that your officemate rearranged their desk and you monitor's image is now shaking. Don't omit anything - even what you feel is inconsequential - leave that judgement to the repair person. Also, what may have changed in your setup, did you move the equipment recently or add a component? What about your cable connections? Did you rearrange the furniture? When was the last time you know it worked properly? What were you trying to do at the time of the failure?

    To paraphrase a famous quote: 'The only stupid or useless information is that which is not provided'. However, unless you really are sure of what you are talking about, don't try to tell the repair person what you think the problem is likely to be. Don't bombard them with technobabble full of buzzwords - any competent tech will see right through that. You can be sure that if you mention that you suspect the expensive flyback is toast, it will be diagnosed as bad. Let them do their job. Listen carefully to their diagnosis. You should be able to tell if it makes sense.

    Searching for Information from USENET Newsgroups

    USENET newsgroups are on-line bulletin boards or discussion groups that cater to every interest from soup to nuts and beyond. There are over 20,000 active newsgroups in existence though for our purposes one is of most interest: sci.electronics.repair.

    There is an excellent chance that your question has come up and resulted in information being passed back and forth on sci.electronics.repair (or other appropriate newsgroup). For example, if you have had problems with a late model RCA/GE television, there have been dozens if not hundreds of postings on this subject over the last couple of years. There is no need to add to the clutter.

    Google Groups (formerly Deja.com/DejaNews) includes a USENET newsgroup searching facility. It has been archiving newsgroup articles since March, 1995. By going to their web site, you can invoke a search of over 45,000 newsgroups (hundreds of GB of data!) for any set of words, names, or email addresses. Within *seconds*, they will provide a list of postings that satisfy your search criteria. Try using Google Groups at least once - you will be instantly hooked. :( Some of the relevant site URLs are:

    Specifically for the sci.electronics.repair newsgroup: This results in listing of threads by date. However, going through the Search page provides many many options to locate specific articles relevant to your problem or just your curiosity.

    While postings typically drop off of your local server in a few days or less, Googlegroups maintains them *forever* so that locating an entire thread becomes a trivial exercise in identifying a search string that will narrow down the postings to those relevant to your needs.

    There are many other services available via Google Groups including newsgroup posting (under constructio apparently during the transition from Deja.com).

    Speaking of posting:

    Posting to the Sci.Electronics.Repair Newsgroup

    This is a bit different than attempting to tell the tech at a repair shop how to do their job - speculation is safer. There is enough cross- checking such that any gross errors in analysis will be uncovered. There is also generally no profit motive. If your speculation is totally bogus, you will find out quickly enough, turn various shades of red - and learn from the responses.

    Even if your ISP doesn't provide USENET newsgroups or allow posting for some reason, you can always access them (read, search, and post) via Google Groups. See the section: Searching for Information from USENET Newsgroups.

    No matter how you do it, however, here are some tips that will get you what you want without unnecessary flame wars:

    Private Discussion Groups and Email Listservers

    In addition to USENET newsgroups, there are a number of private bulletin boards (may also be called forums) on repair related topics. These are accessible via the Web rather than through a News server. New ones come and old ones disappear regularly. :) I personally see little point in using these - traffic is usually very low, and the experts all hang out on the relevant USENET newsgroups anyhow! And, very often the private ones are related to a commercial enterprise as (1) you don't know how whether the replies are slanted toward selling something in some cases and (2) there is often objectionable (at least in my opinion) advertising on the site.

    There are also a few repair related email listservers. These require that you subscribe by sending a special email message and/or filling out a form. Some may have merit in that experts are more likely to be subscribers and they are forced to at least receive all emails (even the next stop is the bit bucket!).

    Sorry, given the relatively low interest in both private discussion groups and email listservers, I can't justify attempting to keep up with their arrivals and departures! :) Both of these can be found through the various tech-tips sites as well as by searching postings on the Sci.Electronics.Repair Newsgroup via Google Groups Advanced Search. A few may also be listed in my Bookmark File.

    Having said that, popular services like Yahoo often host at least a few niche discussion groups that simply due to the number of users, have a volume of traffic worth noting. For example, go to Yahoo Groups and search for "Tektronix". Two groups for Tektronix oscilloscopes will pop up, one for general postings and the other for documentation like schematics.

    There are also some like Fixya.com that aren't generally very technical but may be of use in finding answers to common product-specific repair problems.

    Dealing with a Repair Shop in an Efficient and Professional manner

    When all else fails and you are forced to admit defeat.... OK, I'll try that again: Should you end up taking the equipment to someone else for service, here are some tips for getting it fixed with minimal hassle.

    (From: Rex (bopeep@prysm.net).)

    I have been asked to give tips for dealing with repair shops. It is sometimes difficult for the average consumer to convey their needs to shops or technicians.



  • Back to Troubleshooting Table of Contents.

    Parts Sources

    Where to Go for Parts

    Large electronics distributors like Allied, Digikey, Mouser, Newark, and others stock tens of thousands of types of electronic components. Even Radio Shack can be used in a pinch.

    However, none of these places have even the most basic service parts for consumer electronic equipment. You won't find a single rubber belt, RF modulator, posistor, or video head, nor most Japanese semiconductors within their thick catalogs.

    It may be possible to go direct to the manufacturer of the equipment but expect to spend many times the true price of a part to get it from the horses mouth. In most cases, a totally identical part - with the manufacturer's logo and everything - meeting identical specifications is available elsewhere at a fraction of this cost.

    Web Parts Information and Ordering

    Many manufacturers are now providing a great deal of *useful* information on the Web. For example, Panasonic has a web site you can enter your model number and get a parts list with list prices and part descriptions: This site includes support for Panasonic, Technics, and Quasar consumer electronics. However, my quick visit only showed accessory type items (e.g., replacement original remote controls, cables, etc.). Encrypted credit card protection presumably makes it possible to order parts directly.

    Mail Order Parts Sources

    See the document: "Major Service Parts Suppliers" for some companies that I have used in the past and others that have been recommended. (These lists have now been consolidated into that document.)

    And, Don't Forget Radio Shack

    Radio Shack may be the most abused chain on the sci.electronics.xxx newsgroup hierarchy but they ARE good when it is after business hours for your normal distributors, you need a resistor or capacitor, and just have to have it NOW!

    In addition, Tandy, the parent company of Radio Shack is worldwide and may actually offer a USEFUL selection of components:

    (From Ted Gondert (vcrepair@bbs.industrynet.net).)

    Tandy (aka Radio Shack) has a new catalog available at your local Radio Shack; "Tech America" "Your Electronics Resource". This is special mail order catalog with many parts available from a different division of Tandy. There is no minimum order and parts are sent directly to your house. Shipping is $4.00 for components orders only or various rates up to $13 for orders of $500.

    Call 1-800-877-0072 between 7 a.m. to 11 p.m. M-F Central Time, 9 a.m. to 8 p.m. Saturday, 11 a.m. to 7 p.m. Sunday. Fax 1 800 813-0087. Mail: Tech America, PO BOX 1981 Fort Worth, Texas 76101-1981.

    This catalog, Sept 1997 has 546 pages with capacitors, resistors, transistors, IC, coils, wires, antennas, test equipment, tools, radios, security equipment, books, etc.

    The capacitors include high temperature, 105C electrolytics. The integrated circuits and transistors are mostly American type part numbers, digital, op-amps, etc. not the Japanese type used in most consumer electronics today. But should be many parts that electronics techs can use.

    For example; 1000ufd 16 volt 105C electrolytic capacitor is only 39 cents. (pg 14) That's popular size in use in Panasonic SMPS. Also has MJ15024 audio output transistor for $4.59 (pg 49) and surface mount transistors.

    Radio Shack also has catalogs in stores for RSU, Radio Shack Unlimited. Those show Japanese semiconductors, special batteries, phono stylus, equipment, etc. that your local Radio Shack can order.

    (I haven't ordered anything yet but after checking my inventory and budget will probably stock up on some capacitors, etc. Get most of my parts from MCM, MAT Electronics, etc and some local distributors.)



  • Back to Troubleshooting Table of Contents.

    Troubleshooting of Intermittent Problems

    These are the ones everyone dreads - equipment that is tempermental, working or not working apparently depending only on its own mood. Behavior may appear to be totally random but in most cases, there will be some correlation with physical, environmental, or external interference. Careful observation and perhaps a bit of detective work will ultimately allow a repair to be successful. Troubleshooting such problems is a primary cause of hair loss in engineers and technicians. :) However, with a methodical approach and patience, it should be possible to identify the cause and repair misbehaving equipment. Here are some examples of intermittent problems: This section deals mostly with TVs and monitors since they appear to be most prone to these sorts of problems. This is partially due to the higher power levels and associated heat generation inside of them, and partially due to the cost pressures which result in manufacturing quality control problems. Other equipment like VCRs and CD players also may suffer from intermittent behavior, but it is usually not due to bad soldering (though there are exceptions) but rather due to mechanical problems or dirty or worn internal position sensing switch contacts.

    TV and Monitor Manufacturing Quality and Cold Solder Joints

    Low cost no-name (or unknown name) computer monitors tend to be particularly prone to bad solder connections. However, so are many models of name brand TVs including those from RCA/GE/Proscan and Sony. We'll touch on these at the end of this article.

    Any intermittent problems with monitors that cause random sudden changes in the picture brightness, color, size, or position are often a result of bad connections. Strategically placed bad connections can also cause parts to blow. For example, a bad connection to the SCR anode in a phase controlled power supply can result in all the current passing through the startup resistor, blowing it as well as other components. I had a TV like this - the real problem was a bad solder joint at a pin on the flyback. Thus, erratic problems, especially where they are power or deflection related, should not be ignored!

    Bad solder joints are very common in TVs and monitors due both to poor quality manufacturing as well as to deterioration of the solder bond after numerous thermal cycles and components running at high temperature. Without knowing anything about the circuitry, it is usually possible to cure these problems by locating all bad solder connections and cleaning and reseating internal connectors. The term 'cold solder joint' strictly refers to a solder connection that was either not heated enough during manufacturing, was cooled too quickly, or where part pins were moved before the solder had a chance to solidify. A similar situation can develop over time with thermal cycling where parts are not properly fastened and are essentially being held in by the solder alone. Both situations are most common with the pins of large components like transformers, power transistors and power resistors, and large connectors. The pins of the components have a large thermal mass and may not get hot enough during manufacturing. Also, they are relatively massive and may flex the connection due to vibration or thermal expansion and contraction.

    Why Can't TV Manufacturers Learn to Solder Properly?

    I can think of several potential reasons - all solvable but at higher manufacturing cost.
    1. Mass of large component leads (like shields) does not get adequately heated during manufacture leading to latent cold solder joints. While they may look OK, the solder never actually 'wetted' the heavy pins and therefore did not form a good mechanical or electrical bond.

    2. Thermal cycles and differential thermal coefficients of circuit boards, traces, and solder. While it is not easy to do anything about the material properties, using plated through-holes or a similar mechanical via would greatly increase the surface area of the joint and prevent the formation of cracks.

    3. Vibration. This is also directly related to the single sided circuit boards without plated through-holes to strengthen the joints.

    4. Lack of adequate mechanical support (single sided circuit boards without plated through-holes (vias).
    I believe that the single most significantimprovement would come about by using plated through-holes but this would add to the cost and apparently the consumer is not willing to pay more for better quality and reliability! Some designs have used rivlets - mechanical vias instead of plated ones. While this is good in principle, the execution has often been flawed where cold solder joints resulted between the rivlets and the circuit board traces due to lack of adequate process control.

    The Sony and RCA/GE tuner shield problem is interesting because this could have been solved years ago at essentially no additional cost as other manufacturers - and their own repair procedures - have proven.

    Attacking intermittents

    First, determine whether the problem is internal or external.

    The most common external causes would be electro-magnetic interference, either through the air or via the power line. For more on these in particalur, see information on interference in the documents on TV and monitor repair. But, suffice it to say, changing the location or electrical power source will usually help to narrow it down.

    If internal, it may be physical, heat related, or mode related. Gentle whacking (yes, whacking is an acceptable diagnostic technique but don't go for the 12 pound hammer!), pressing, flexing, cable wiggling, etc., can and should be used in an attempt to confirm at least that there is a physical cause inside the unit. Doing these tests just as the problem comes or goes is the best time as whatever is marginal, will be most marginal then.

    If the problem appears or disappears, or does both, over a period of time after the equipment is turned on, then temperature is almost certainly a factor as the circuit board and components expand.

    The most common physical problems are bad (cold) solder joints, connectors that need to be cleaned and reseated, and bad cables or cable connections. Perhaps surprisingly, though components may fail internally and result in erratic behavior, this is probably lower on the list of likely causes than those listed above. Some exceptions would be mechanical relays in audio power amplifiers, phone equipment, and elsewhere; hybrid power amplifiers, and other power devices.

    The whacking, etc., can be done without taking the cover off the equipment and may or may not reveal anything. In either case, you will have to go inside. But if there is an effect, then you will know that the problem IS inside and further tests will need to be done to identify the specific cause.

    Once the cover is off, there still may be quite a challenge to find the specific solder connection or contact that needs attention. Knowing something about how the actual circuit area relates to the symptoms will help narrow it down. For example, if there is a loss of vertical deflection in a TV or computer monitor, the most likely areas to attack will be the vertical deflection output stage and its power supply feed.

    For popular consumer electronic equipment, intermittent problems are often present in many (or even most) samples of a particular model over the course of its life. Therefore, checking a tech-tips database or asking on the USENET newsgroup sci.electronics.repair may reveal a common cause and an easy solution ("resolder the flyback pins"). There are a list of tech-tips databases at my Web site, www.repairfaq.org.

    (From: Phil Buble N1GTZ (muttnik@ecr.net).)

    A note on whacking as a troubleshooting technique, at home and in the shop.

    I'm not what you would call a full time electronic repairman though I have made a living doing it commercially. I can be just helping a friend out at home but usually it's been an adjunct to my main work as assembler/post flow touch-up and I'm pretty good at it. Therefore most of my repair experience is with new equipment that doesn't work correctly the very first time it's powered on. (and yes when *will* that wave-solder machine learn to solder? :) Running that thing is a art-form I'm glad to avoid)

    Naturally in such a situation I'm a great believer in "swap-out with NGP testing" since there's usually lots of them in an assembly shop but this cannot always be easily done. Especially at home, with obsolete units or those so small or cheaply made not a vacuum tube, IC or module is to be found in a socket. My funniest experiences with whacking regard these - one commercially and one at home. The commercial one first:

    It involved a totally obsolete and smallish sensor board used in the ground-water monitoring industry to measure water pH deep down in wells. Even carefully sealed you can imagine the condition it was in after years of hard use. Only a few had ever been made by the company long before and the engineer who designed it equally long gone. A young, recently hired engineer was given the task of finding out what was wrong. It was giving rather useless and erratic readings and needed to be repaired in a hurry. I cleaned it and reflowed all joints, just in case, then turned it over to him since it still didn't work. After hours of frustration and attempts to get "into the head of the designer" he gave up and I asked to give it a try. By then I had a hunch. I made a routine test to make sure all was getting power - then gave the PCB a whack and a little twisting action. It began working perfectly as long as the PCB had a slight twist to the right. This literally took me all of about 5 minutes. You have never seen such a dumb-founded engineer! They do need to get out more! Even with the failure mode detected the cracked trace could not be found in a reasonable time so I had the honor of transferring all the parts to a new PCB. Amazing they even had one.

    The second funny situation occurred many years before the above and happened at home. A neighbor brought over a old (even for the time) but nice condition 19" tube-type B/W TV hoping I could fix it. Fully half this set was point-to-point wiring, no PCBs at all. I'm old enough to have one foot in the all tube and "condenser" era and one foot in the transistorized world so it didn't matter to me that it was tubes. As long as my friends are willing to pay for the parts and hopefully locate a schematic I'm willing to at least try. It's all done in a casual sort of way. (Side note: You'll have to pry my Heathkit AA-100 Vacuum Tube Stereo Amp from my cold dead hands, it still sounds great 41 years after it was built)

    This one located the Sam's Photofacts for it, complete with schematic and pin voltages. A resistor in the B+ line to the plate of the Horizontal output tube had burned out. That was replaced and all DC pin voltages then looked OK - yet no picture. Sure, the H Oscillator wasn't oscillating! The next logical thing to do was to swap-out the H output tube with another to see what happened. I told my neighbor we needed to locate a tube, and a rather expensive one, to go any further. He didn't bother, it wasn't worth the effort or expense. 5 *YEARS* later he trots out that same TV hoping, once again, I could get it to work. I tell him we still needed that tube. He shrugs, plugs it in, turns it on and gives it a good whack. It came on and worked perfectly! That's all it needed all along, my power-supply repair had fixed it 5 years before but no one ever whacked it to get it started again.

    Selective circuit whacking's been one of my most productive and time saving

    Inspection and Power Off Tests for Intermittents

    Assuming these don't help (or you consider letting someone else solve your problem to be cheating), a detailed visual inspection is the next step. This may be all it takes. With the unit unplugged) and after confirming that power supply capacitors are discharged!), remove the cover. Where a problem is found, don't assume there is only one! In many cases, bad solder connections or bad crimps are caused by poor manufacturing process control and will be repeated in many locations. So, correct what was found and then continue to inspect the entire unit. Sometimes, manufacturing is so poor that resoldering the entire board is the only solution with any chance of long term success.

    Power On Tests for Intermittents

    If none of this produces a breakthrough, the next step is to power up the equipment. WARNING: Depending on the particular equipment, lethal voltages or other hazards may exist. Make sure you understand and follow what's in the document: Safety Guidelines for High Voltage and/or Line Powered Equipment. Don't rush this process. It may take several diagnostic sessions to finally resolve the problem. Even if one or more cracked solder joints are found and fixed, it may be worth waiting a few days to reinstall those 10 shields that had to be removed in order to access the underside of the main board! However, do replace the cover so that the internal temperature will be similar to normal during extended operation.

    Now the question comes up: How can the re-occurrence of intermittents be prevented? For cracked solder joints, in addition to using proper soldering techniques for repair, it should be possible to add some "reinforcements" in the form of bare wire wrapped around the pin and extending out to the circuit board trace or even to an adjacent component pin. This will be better than just using more solder. For the CTC175 etc. cases discussed below, there is also special "elastic" solder that supposedly should be used. But, there are mixed reviews on whether this really helps.

    Some equipment may also benefit from a small amount of additional cooling. A small fan can be added to draw air out of the cabinet. This will improve reliability since most components are happier being cool but will also reduce the extent of the thermal cycles reducing the likelihood of bad solder joints developing in the future.

    RCA/GE/Proscan and Sony TVs

    One of the classic examples of an intermittent problem that is present in an entire product line are the RCA/GE/Proscan TV chassis starting with CTC175 and running at least through CTC187, possibly beyond. A very large percentage of these TVs are destined to have cracked solder joints in the area of the tuner/controller resulting in erratic picture and sound. If not corrected, this eventually results in bad data being written into the EEPROM that stores the TV's parameters causing total failure to turn on. Until recently, Thomson Electronics was covering at least part of the repair costs. There may also be at least one class action lawsuit pending in regards to this problem.

    Some Sony TVs suffered from a similar set of bad solder joints, usually in the tuner or IF (metal) boxes. The most common location for the problem for many of these was to one pin of a coil inside the IF box which always seemed to lack adequate solder.

    Much more information on the RCA/GE/Proscan and Sony solder problems and solutions, see the documents: RCA/GE TV CTC175-187+ Solder Connection and EEPROM Problems and Sony TV Tuner and IF Solder Connection Problems.

    Other makes and models of TVs have similar problems with solder joints but not to the extent of these.



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    Perfecting Your Skills

    Where to Find Equipment in Need of Repair or Abuse

    Now that you have read all the previous sections, perhaps some of the Repair Briefs, followed the sci.electronics.repair newsgroup for a while, built your handy widgets(tm), and loaded up on test equipment, where should you go to find broken stuff to play with and practice on? Of course, you probably have closets bulging with broken VCRs, TVs, stereos, and small appliances. You may not may not want to practice on these just yet.

    The most annoying situation is when after haggling over the price of a 'dead' VCR, you get it home with great expectations of the challenge ahead only to find that it works perfectly or your Mark-I thumb is all it takes to clean a supposedly trashed video head (but you do have to know the proper technique and incantations!) I ended up with a couple VCRs like that. A 'dead' CD player for $5 magically cured itself on the back of my 10 speed bicycle. Often problems are simple and easily remedied resulting in quick gratification. However, there will be real dogs which could more than make up for the easy fixes (like the GE TV with the never ending string of bad solder connections). At least, if you sell the easy ones, this will help pay for your 'habit'.

    One note: inspect whatever you take home. Cockroaches and other unwelcome visiters may have made a comfortable home in that old TV. I once picked up a nice toaster oven but found that I was baking more than I expected or desired and had to completely disassemble and clean it before the cockroaches stayed away permanently.

    Paul's Comments on the 'Well Equipped Garage or Flea Market Sale-er'

    Only read the following if you are serious about this! Note: these comments apply more to the electronic flea markets or ham fests found around high tech parts of the country but can be adapted for the back woods as well.

    (From: Paul Grohe) grohe@galaxy.nsc.com).)

    Ah! If you are really serious about buying equipment, carry one of those little 200W 120VAC inverter bricks *with you* in your backpack, along with a cigarette socket to car battery clip adapter. Keep a small marine or gel-cell battery in your car (or with a friend who has a table).

    This way, when you "roll up" on a good deal, ask the seller if you can borrow his cigarette lighter, or car battery, for a few minutes. If you can't use his car (and if you have time), run back and get your battery.

    If he refuses...There's your answer!

    I keep an 8-cell "AA" battery holder and an assortment of pigtail power connectors in my backpack. This way, I have an adjustable 1.5 to 12V power source to test things there on the spot (I'm planning on making a complete test box, complete with ammeter and current limiting).

    I also carry a bunch of "AAA" and "C" cells in my backpack ("C" cells can be shimmed into "D" holders with a few coins between the batteries).

    The same rule applies, If they won't let you test it.....etc,etc,etc.

    Will they give you their business card or phone number? Make it clear you will not bother them unless absolutely necessary (secretly write down their license plate number, for "Justin Case").

    Also carry a pocket DMM (This is a *must* for any flea enthusiast - NEVER buy batteries w/o testing them first!) and a small, bright flashlight (for "inspections").

    Smell the equipment too! This can be a big clue as to it's condition. Does it smell like something blew up? Does it smell musty or moldy?

    Another clue I have found is the physical condition of the unit. Sometimes the "cleanest" unit of the bunch is the one that failed prematurely and got stuffed on a shelf or back in the box. Whereas the "used looking" units were just taken out of service.

    More importantly than "functional", is "complete".

    Nuthin' worse than getting something and finding out a piece, or a board, or a module, or an expensive or rare IC is missing. Now you know it's not functional, and there may be little chance of it even becoming functional again.

    I always assume "dead" until happily proven otherwise. Follow your instincts! If you have doubts, there's a reason! I always consider the scrap value of the item also. Any expensive goodies in it? The power switch may be worth more than the item!

    Some of my best deals were the "I don't know if it works...Oh,..five bucks" deals.

    It's a gamble...Ya' win some, ya' loose some!

    Caveat Emptor!!!!!

    (Let duh buyer beware!)

    Cheers.

    And, How Paul Equipped His Home Lab

    (From: Paul Grohe) grohe@galaxy.nsc.com).)

    That's me! Flea Markets/Surplus Stores/Salvation Army/Goodwill/thrift stores/Garage-yard Sales/etc...And there is *lots* of good stuff around this area!

    I call it "going' Junkin'".

    I arrive at about 5:30 AM, so that requires a combo krypton spotlight/fluorescent lamp flashlight (a $3 Goodwill special :^).

    I carry with me the aforementioned 8 cell battery pack, 8 "C" batteries, a bright krypton penlight, one of those all-in-one screwdriver/knife/pliers/scissors/bottle opener contraptions ("fishermans friend"?) and a small pocket DMM. All about 5-7 pounds total. I carry it all in a backpack that I wear "backwards" on my chest (for easy access). During the "lull" (around 9 AM), I go back and "load transfer" to the car.

    I got it down to a science!! ;^)

    After some lucky "scores", and a few *hundred* hours of troubleshooting, I have a *very* well stocked home lab... :^)

    My home lab is graced with a Tek 576 Curve tracer (bad Xfmr), HP 5345 Freq cntr (bad NPN trannie), HP3456 DMM (bad ROM), Radiometer 106 RF Generator (stuck keys), Genrad 1688 Digital RCL meter (another bad ROM) and a "few" other assorted goodies...

    The Tek 576 is my favorite. This unit was the one of the bunch that failed early and was shelved. It was dusty, dirty, full of spider webs, and missing one little knob, but in otherwise perfect shape. I got it for $200. Guys were offering me $750 for it "as-is" on the way back to the car! To top it off, two tables down from where I got the 576, someone was selling a *complete* set of the transistor/diode plug-in fixtures. Score #2!

    It was a good day..... I used up all of my allocated "luck" for that year. :^)

    The 576's collector supply transformers primary was dead-shorted. Eventually I was lead to Dean Kidd, who sold me a *brand new* one for $75! Tek even took the bad transformer back for failure analysis!

    The HP frequency counter was the longest fix (~2 months). It's all jelly-bean TTL logic (some ECL), but no "brains" at all! Board swapping with a friends unit and some "shotgunning" brought it to back life. The eventual root failure was a single NPN transistor, in a buffer between two stages of the main 500MHz counters, whose beta had dropped significantly. I stuck a 2N2222 in there to check it out, and "there" it remains to this day!

    The Genrad was the "hair-puller" (really made me begin to doubt my troubleshooting skills!). It would continually fail it's self check at the same step. The failure code indicated a certain section of the analog section, which I *knew* was okay. There is not much to the analog section anyways! It is mostly jelly-bean, off-the-shelf 74C series digital logic sitting around a 6502 uProc. After checking *every* analog part (most out-of-circuit), and swapping all of the digital chips, I concluded it *must* be the ROM. It was the only part left that had not been replaced! I posted for a "brain donor" and got a reply. He had two dead units and offered to send me the ROM's to compare and read. I took him up on his offer and copied the ROM, and then transferred it to an EPROM. Voila! The f#@&!#g thing worked! I chased my tail for weeks! It turns out that a few bits in the ROM were corrupted, and the error was subtle enough to cause it to just "trip-up" at that phase of the self-test, even though the hardware was fine. Arrrgghh!! I sent him his ROM's back, with a little "thank-you", and eventually helped him revive his two units. This was one of those "fun" repairs.

    Everything else I have was dead, dying or crippled (er, "functionally challenged"). I even had to repair my 475A O'scope before I could use it! (It's a "P-I-T-A" to troubleshoot a scope w/o a scope!)

    Too Bad About the Good Old Days

    (From: Mike Diack (moby@kcbbs.gen.nz).)

    In the days before 'Weirdstuff Warehouse' stopped being weird and simply became boring, a lot of the junkus electronicus they sold bore a sticker stating:

    This equipment is guaranteed not to work - should you find that it does, we will be happy to exchange it for something that doesn't.

    Treat fleas the same.

    (From: Paul Grohe (grohe@galaxy.nsc.com).)

    Yep! I bought a lot of "goodies" with that little orange and black sticker!! I resisted the temptation to take it back if it worked. If it did work, I broke it, then fixed it, so then I would not feel so "guilty". ;^)

    Harrie's Notes on Repair

    (From: Harrie Gulikers (hgu@oce.nl).)

    Just want to share my experience on repairing electronic devices in general. After many (most successful) repairments I've concluded the following:

    These bad contacts were the cause for, say 75% of all devices I have repaired for the past 16 years. If (and IF) a component was damaged, it was because of bad contacts.

    Take this advice in mind and I hope you can profit from it. Repair shops probably will throw a stone towards my head ;-)

    Roger's Comments on Troubleshooting

    (From: Roger Pariseau (grinder@west.net).)

    The closest I ever came to bench tekking was when I would service electronic organs at a dealer's warehouse. If I spent all day there I'd normally fix upwards of 20 instruments and "check out" several others. Normally I just "ran traps" at churches, auditoriums, schools and homes where I got to five or six instruments a day.

    I dealt with intermittents via a little rubber mallet and a can of cold spray!

    And, I learned a couple of things:

    1. 'Shotgun' a bad circuit.

    2. If an amp's outputs are blown, check/replace the speakers also

    3. Digital circuits are *not* logical!

    4. Never hurry.

    5. Check *all* supply voltages first.

    6. Check all signal generation and their paths (some organs derived their rhythm section's clock from a generated note - there are similar circuits in TVs).

    7. Burn-in your work - it can go out the next day.

    It was a great little business until the mid '80s when the Casios and the Yamahas became popular. Now I mostly repair computers with the occasional piece of HiFi gear hitting my bench. Like that damned Sony 100-disc CD player that I can't find parts values for!



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