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Copyright © 1994-2008
Reproduction of this document in whole or in part is permitted if both of the
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1. This notice is included in its entirety at the beginning.
We will not be responsible for damage to equipment, your ego, county wide
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material.
The video cassette recorder is a wonderful example of extremely complex
precision technology that has been made affordable through mass production.
In general, it is usually quite reliable. Treat a modern VCR with a bit
of respect and it will provide trouble free service for a long time.
Unlike a TV where the power circuits take their toll on circuit components,
the electronics in VCR are generally quite reliable and rarely fail. Most
VCR problems are mechanical - dirt and dust in the tape path, deteriorated
rubber parts, dried lubrication, wear of precision parts including the
spinning video heads, and abuse caused by rocks, toys, and peanut butter and
jelly sandwiches.
Note: Links to all the diagrams and photographs referenced from this document
can be found in Sam's VCR FAQ Files.
Even if you are a technoklutz who lets your kids change the light bulbs in your
house and would never consider tackling any actual repair or internal
maintenance of your VCR, some basic awareness of the principles of video
recording and the likely causes for common problems will enable you to
intelligently deal with the service technician. You will be more likely to
be able to recognize if you are being taken for a ride by a dishonest or just
plain incompetent repair center. For example, did you know that one of the
most dreaded of problems - the tape eating VCR - can often be remedied by
a thorough cleaning and a 50 cent rubber tire?
This document will provide you with the knowledge to deal with over 85% of the
problems you are likely to encounter with your VCRs. It will enable you to
diagnose problems and in most cases, correct them as well. First and foremost
are the techniques for cleaning of the tape path and replacement of rubber
parts like belts, tires, and the pinch roller - the solution to many common
problems with VCRs. With minor exceptions, specific manufacturers and models
will not be covered as there are so many variations that such a treatment would
require a huge and very detailed text. Rather, the most common problems
will be addressed and enough basic principles of operation will be provided
to enable you to narrow the problem down and likely determine a course of
action for repair. In many cases, you will be able to do what is required
for a fraction of the cost that would be charged by a repair center.
Should you still not be able to find a solution, you will have learned a great
deal and be able to ask appropriate questions and supply relevant information
if you decide to post to sci.electronics.repair. It will also be easier to do
further research using a repair text such as the ones listed at the end of
this document. In any case, you will have the satisfaction of knowing you
did as much as you could before taking it in for professional repair.
With your new-found knowledge, you will have the upper hand and will not
easily be snowed by a dishonest or incompetent technician.
If you need to send or take the VCR to a service center, even a simple repair
could easily exceed half the cost of a new VCR. Service centers
may charge up to $50 or more for providing an initial estimate of repair
costs but this will usually be credited toward the total cost of the repair
(of course, they may just jack this up to compensate for their bench time).
If you can do the repairs yourself, the equation changes dramatically as
your parts costs will be 1/2 to 1/4 of what a professional will charge
and of course your time is free. The educational aspects may also be
appealing. You will learn a lot in the process. Thus, it may make sense
to repair that old clunker so the kids will have their own VCR or you will
have a convenient means of copying tapes (legally, of course).
BTW, if you ARE one of those individuals (and there are bucket loads) who
doesn't bother (or doesn't know how) to set the clock on your VCR, there is a
solution - at least the next time you need to purchase a new VCR. These
machines search for a TV station that includes the time code in its
transmission format (it is in the vertical blanking interval should you care)
and automagically sets the VCR's clock from that information. There - no
more flashing 12:00! Many VCRs have this feature nowadays.
Prior to practical video tape recording, the only way to preserve a TV
show was to use special equipment that essentially made a film of it off of a
video monitor. The quality of such recordings was not very good, editing
was difficult, the film needed to be developed so playback was not
immediate, and of course, the film could not be erased and reused.
The first successful commercial video tape recorder was introduced around 1956
with the Ampex Quadplex - a $50,000 machine using 2 inch open reel tape and
a high speed spinning head with 4 pickups rotating across the tape. This event
revolutionized commercial broadcasting. However, this technology was much too
complex, cumbersome, and expensive for consumer use and has a number of
technological disadvantages as well.
For a consumer video tape recorder to be successful it was felt that the
following three major hurdles had to be overcome:
The rotating heads of the Quadplex machine provided the needed
tape-head speed to achieve sufficient video bandwidth. However, the transport
was much too complex for a consumer machine. Another disadvantage
was that since a video frame consists of many adjacent tracks on the
tape (16), special effects like stop motion as well as forward and reverse
search were not possible without a frame store. While this would not be
out of the question today, the cost of such a device in the 1950's would
necessitate the consumer taking out a second mortgage to pay for it.
Finally, the 2 inch wide format required too much tape for achieving
a cost effective 1 hour program time and made the design of a manageable
cassette an impossibility. A separate room would be needed to house a
modest size video tape library!
Helical scan overcomes most of these problems. See:
Helical Scan Video Head Assembly. Rather than
scanning across the tape, the tape is wrapped a bit over 180 degrees around a
rotating drum at a slight angle. Thus, successive tracks are written
diagonally across the tape and can thus be much longer than the width of the
tape as in the Quadplex. The tape, therefore can be rather narrow. The first
helical scan tapes used a 1 inch format but narrower tape soon followed.
The most common formats today are forms of VHS (and Beta) at 1/2", and 8 mm
(mostly used for portable applications in camcorders and data storage.)
4 mm tape is used for high quality audio (DAT) as well as data storage.
Each VHS track corresponds to 1 field of the interlaced video format. See:
VHS Tape Format. Generally, two heads opposite each
other on the rotating head drum are used. One rotation of the drum
corresponds to a complete video frame with heads designated A and B for the
even and odd fields respectively. What this also provides is the ability to
easily implement a variety of special effects including freeze frame, and
fully variable speed forward and reverse motion with a recognizable and in
many cases, quite clear picture. With relatively minor restriction, this
becomes as simple as moving the tape forward or backward or keeping it
stationary.
For a not too terrible ASCII diagram and additional discussion, also see the
section: VHS physical tape format
(Camcorders and other compact systems may use 2 pairs of identical heads
where the opposing pairs are separated by 270 instead of 180 degrees.
Physically, there are 4 heads spaced equally around a drum 2/3rds the size
of the normal VHS drum. However, successive head in the sequence is 270
degrees apart. In other woeds, if the heads are numbered 1,2,3,4, they are
used in the order: 1,4,3,2,1,4... This permits the use of a smaller, lighter
video drum but the recorded format is identical.)
The A and B heads are not identical either. Their azimuth angle differs
being +6 degrees for one and -6 degrees for the other. See:
VHS Video Head Pair Azimuth Angles. This is one of
several techniques used to minimize crosstalk between adjacent tracks.
Azimuth angle is how far the head gap is from being perfectly perpendicular
to the direction of tape-tape motion. For example, a head with an azimuth such
as / will ignore most of the information recorded with an azimuth of \.
Note that the head gap - the distance between pole pieces - is on the order
of 1 um - 1/25,000 of an inch. As a point of reference, a human red blood
cell is about 7 um in diameter and an average sheet of typing paper is
about 100 um in thickness. The gap is filled with a nonmagnetic material
to prevent it from getting clogged and to force the magnetic flux out
of the head structure and into the tape magnetic coating. This remarkably
fine spacing is necessary to achieve the multimegahertz video bandwidth.
Actual tape motion for a VCR is remarkably slow. To someone familiar with
audio decks, the tape in a VCR even at SP speed (the fastest) seems to
be crawling along. Their first reaction is often one of: "there must be
something wrong as the tape is moving sooo slooowly." Nope, just amazing
technology. The SP speed of a VHS VCR corresponds to a linear
tape speed of only 1-5/16 ips - slower than for an audio cassette deck
(1-7/8" ips). EP speed is 1/3 of this - 7/16 ips. However, the effective
tape speed as seen by the video heads is over 15 feet per second due to the
spinning video head drum.
The luminance (Y) and color (C) components of the composite video signal are
recorded differently. Luminance, which is in effect the black and white
picture with all the high resolution components but no color, is
frequency modulated on a carrier at around 3.4 MHz. The deviation is
about 1 Mhz and the maximum frequency recorded on a VHS tape is a little
over 5 Mhz (Beta is slightly different and S versions of Beta and VHS
extend some of these to achieve higher bandwidths. The color signal
is separated from the composite video and is amplitude modulated on
a 629 kHz carrier. This is called the color under' system. The 'U'
in U-Matic, a very popular industrial VCR 3/4" format (which predates
Beta and VHS and is still in use) stands for this.
Since the head-tape speed for the VHS audio track is the same high rate as
for the video track and exceeds that of a typical audio cassette deck by a
factor of more than 100, VHS HiFi audio reproduction - frequency response,
signal to noise ratio, and dynamic range - is excellent and approaches
that of a CD. In fact, using a T120 video cassette in EP (SLP, 6 hour)
mode simply to record stereo music (with the video ignored or blanked)
is extremely cost effective. What other media/technology will store a 6 hour
concert with nearly perfect reproduction for under $2? (Note: if you do
this, some VCRs will require some kind of video input to maintain stable
tape speed. You can just ignore the video portion on audio playback.)
There are two disadvantages to VHS HiFi, however: (1) there may be some
degradation of video quality due to unavoidable interactions with the buried
audio, and (2) it is not possible to rerecord (dub) only the audio without
disturbing the video. The only way to do this without copying the video to
another tape would be to read out the video and hold it temperorily in a
double buffered frame store for subsequent recording back onto the tape after
the new video was laid down. However, this would put the video 1 frame behind
where it was thus complicating the situation. So, audio dubbing simply isn't
supported.
With 8 mm, there is no separate linear audio track - all audio is HiFi using
the spinning video heads.
Record: reference signal is vertical sync pulse from video input:
Play: reference signal is timing pulse derived from quartz oscillator:
Really slow speed is usually implemented as a variable frame advance with
the tape fully stopping between frames. Special sets of video heads provide
the best quality. Freeze frame (PAUSE) uses the same set of heads. As with
CUE and REV, acceptable picture quality is provided even with a 2-head VCR
for EP speed recorded tapes. In all cases, picture quality can be further
improved through the use of a digital frame store.
Note that the servo systems in consumer VCRs are rarely precise enough to
implement the kind of instantaneous forward or reverse frame advance that
is present in high performance (and high cost) editing decks having jog
shuttle knobs with instantaneous and precise response.
Philips/Magnavox used to have a very nice on-line introduction to a variety
of consumer electronics technologies. Although their site has disappeared -
and even people who work for them have no clue - I have now recovered
several of the articles including those on TVs, VCRs, camcorders, satellite
reception, and connections. See the Introductory Consumer Electronics
Technology Series. These as well as most or all of the other articles,
as well a glossary and much more, can be also
be accessed via the Internet Archive Wayback
Machine. Copy and paste the following URL into the search box:
The earliest (Nov 09, 1996) archive seems to be the most complete.
Also check out:
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.
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.
This site includes a relatively short but fairly complete VCR repair guide
that covers most of the common classes of problems - with nice diagrams to
help with the explanations.
The VCR-only tech-tips database is clearly indexed by manufacturer and model
number. Every repair includes a level-of-difficulty rating - which is handy!
Many include layout and parts placement diagrams as well.
The developers of this site also sell a variety of generic VCR repair parts,
tools, and TV remote controls.
My only real complaint is with respect to the annoying flipping banner at the
top of their main pages! :-(
In addition, modern VCRs are NOT built like the Brooklyn Bridge! The
weight of a TV or stereo components could affect the VCR mechanically,
messing up tape path alignment or worse.
I would avoid brands you never heard of. K-mart brand, Recoton(sp), the street
vendor from whom you buy Chinese food, whatever.
Higher grade tapes are not necessarily worth the expense but in my experience
with some like Maxell and Scotch, going one level up from the cheapest is
worthwhile and results in a noticeably better picture.
Only a few companies actually manufacture the raw tape stock. For what it's
worth (FWIW), I have used Scotch in the past. It was inexpensive and the
quality was good and consistent. I haven't purchased video tape in quite
awhile now so I do not know if this is still true (Winter 2003).
The higher grade tapes may actually be harder on the video heads due to
their formulation but this probably doesn't matter for the ordinary user..
You don't need HiFi grade tapes for HiFi - any tape will work. However,
higher grade tapes may last longer with higher quality results in demanding
situations like 24 hour a say security monitoring.
Consumer Reports does a review every so often, check back issues. I believe
their conclusions were generally to buy name brands by price. Whether you
believe in Consumer Reports or not, checking their ratings at least gives
you an additional data point.
I have not seen any "official" guidelines on tape longevity for a long time,
since the Beta days. Use of old tapes will not generally ruin video heads but
may clog them. Proper manual cleaning restores normal operation.
Your mileage really depends on several factors, the most important being the
conditions under which it's used. I've seen VCRs that can chew up a tape in
one or two passes and make it unusable. High humidity and heat will cause
tapes to stick to the head drum and wear prematurely. Shuttling tapes back and
forth and leaving them sit in pause (on one spot) can accelerate wear.
Under ideal conditions: clean machine in good alignment running a tape from
beginning to end without stopping is as good as you're going to get. Alignment
tape manufacturers used to indicate expected life as the "number of passes".
No significant degradation in 50 passes, but after that, dropouts become
obvious. Maximum life is 200 passes. At that point, the tape is starting to
break down with oxide particles being shed onto the heads (actually happens
with all tapes to some degree) causing head clogging. With tapes of any age, a
liquid spill such as soda pop ends the game right there. It can be cleaned,
but unless it's your precious home movies, forget it.
I would use a tape until the dropouts become annoying. Dropouts are places on
the tape where the oxide is missing. You'll see them more at the beginning of
a tape where it's mechanically stressed by loading and unloading. A lateral
scratch on a tape (caused by buildup of gunk in a VCR) will show up as a 3 or
4 line continuous dropout somewhere on the screen. Look at some heavily used
rental tapes and you'll get the idea. So, bottom line: use it until it shows
it's age. :)
If you want some guidelines, see the next section:
Sample VCR preventive maintenance schedule.
Realistically, you are not going to do any PM anyway. So, just be aware
of the types of symptoms that would be indications of the need for cleaning
or other preventive or corrective maintenance - erratic loading, need
to convince the VCR to perform certain operations, whirring motors without
completing cycle, VCR taking longer to go into or out of a particular mode
than you recall, jittery or noisy picture, or wavering or muddy sound.
If your inspection reveals deteriorated rubber parts, obviously these
should be replaced regardless of their age.
Of course, acute symptoms like a tape jam or tape munching episode is a
sign of the need for emergency treatment. This still may mean that a
thorough cleaning is all that is needed.
I generally don't consider cleaning tapes to be of much value for
preventive maintenance since they do not run long enough or with enough
force to clean the rollers, stationary heads, and guide posts. Also,
the dry type, in particular, are abrasive and frequent use may cause
premature wear to the expensive video heads.
The following are some reasons to inspect and clean a VCR periodically:
If you follow the instructions in the section:
General guide to VCR cleaning and rubber parts
replacement, there is minimal risk to the VCR. However,
don't go overboard. If the belts are in good condition (by appearance and
stretch test), just clean them or leave them alone. This is especially true in
the (generally infrequent) designs of some models of VCR tape transports where
significant disassembly is required to replace a belt. In this situation,
you risk not being able to put everything back the way it was. Most belts can
be replaced with little or no disassembly beyond removing the top and
bottom covers and possibly any circuit boards that may be in the way,
Sometimes one or two additional screws will need to be loosened or removed
to move a bracket or shield.
It is not clear here what a 'tape' is though the comments that go along with
this table seem to indicate that it means a T120. However, parts that deal
with tape loading are affected not by how long a tape is played but by the
number of loading cycles. Wear on the video heads, on the other hand is
strictly a function of play/record time. Wear of the A/C and erase heads
depends on both time and tape speed. Thus, these are additional reasons
not to take the numbers below too literally.
Note: if you should ever damage a rental tape as a result of a cranky VCR
or for any other reason, don't just give it back to the video store. Please
let them know. Also, if your VCR should jam with a tape inside, do not
forcibly extract it - read the appropriate sections later in this
document. If in doubt, let the video store know what happened and
follow their recommendations.
Given that you are not likely to give up the movie couch potato addiction,
some problems can be avoided by fast forwarding a couple of minutes into
the tape before hitting PLAY. Damage to rental tapes often occurs near the
start - and this will avoid some of the useless coming attractions as well!
If you notice the video breaking up or deteriorating while you are watching,
immediately ejecting the tape may be the most prudent option since the worst
may be yet to come!
While I cannot control your viewing habits, playing a lot of old, dirty,
deteriorated tapes (rental or from your own tape library) will eventually
take a toll on your VCR. At the very least, you should perform a general
cleaning and inspection at more frequent intervals.
(From: Jim Lagerkvist (jlager@tir.com).)
Renting a video tape has all the same potential consequences as renting
a hooker. That tape may pass to your machine anything from pizza grease
to splices made from duct tape or staples. I keep two VCRs in my house.
One for rental tapes and another for known trusted tapes.
The type of air cleaner that's most likely to be a problem are probably
those that supposedly emit negative ions and/or ozone (activated oxygen,
O3). These are typically more expensive and some models show up on eBay
and in up-scale catalogs.
Stay away from the line side of the power supply - put electrical tape over
the exposed connections. To be doubly sure, tape a piece of cardboard or
thick plastic over the power supply section. Other than that, there is
more danger of damaging the VCR by accidentally shorting something out
or breaking a little plastic doodad than of you getting hurt.
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).
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.
Pill bottles, film canisters, and plastic ice cube trays come in handy for
sorting and storing screws and other small parts after disassembly.
Select a work area which is well lighted and where dropped parts can
be located - not on a deep pile shag rug. Something like a large plastic
tray with a slight lip may come in handy as it prevents small parts from
rolling off of the work table. 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.
Another consideration is ESD - Electro-Static Discharge. The electronic
components in a VCR are vulnerable to ESD. There is no need to go overboard
but taking reasonable precautions such as getting into the habit of touching
the chassis first before any of the electronic components is a good practice.
The use of an antistatic wrist strap would be further insurance.
A basic set of precision hand tools will be all you need to disassemble
a VCR and perform most adjustments. These do not need to be really
expensive but poor quality tools are worse than useless and can cause
damage. Needed tools include a selection of Philips and straight blade
screwdrivers, needlenose pliers, wire cutters, tweezers, and dental picks.
A jeweler's screwdriver set is a must particularly if you are working on
a portable VCR or camcorder. For adjustments, a miniature (1/16" blade)
screwdriver with a non-metallic tip is desirable both to prevent the
presence of metal from altering the electrical properties of the circuit
and to minimize the possibility of shorting something from accidental
contact with the circuitry.
You should not need any VCR specific tools with the possible exception of a
miniature metric hex key wrench set for loosening the set screws on the
roller guides should you need to perform a tape path alignment. I have
never needed a VCR head puller. You can make a tool for the special nut
found on many A/C head assemblies for tracking adjustment by filing a
slot in the blade of a straight blade screwdriver.
A low power fine tip soldering iron and fine rosin core solder will be
needed if you should need to disconnect any soldered wires (on purpose
or by accident) or replace soldered components.
CAUTION: You can easily turn a simple repair (e.g., bad solder connections)
into an expensive mess if you don't have both a decent soldering iron and
the soldering skills to go along with it. If in doubt, find someone else to
do the soldering or at least practice soldering on a junk circuit board first!
See the document: Troubleshooting and Repair of Consumer
Electronics Equipment for additional info on soldering and rework techniques.
For thermal or warmup problems, a can of 'cold spray' or 'circuit chiller'
(they are the same) and a heat gun or blow dryer come in handy to identify
components whose characteristics may be drifting with temperature. Using the
extension tube of the spray can or making a cardboard nozzle for the heat
gun can provide very precise control of which components you are affecting.
Basic cleaning supplies include Q-tips (you may know them as cotton buds)
for everything BUT video heads, chamois covered cleaning sticks (for video
heads), lint free cloths or paper towels, water, and isopropyl alcohol
(preferably 91 percent medicinal grade or better).
For info on useful chemicals, adhesives, and lubricants, see the document
"Troubleshooting of Consumer Electronic Equipment".
If you have several VCRs or do repairs for friends (former friends?),
there are inexpensive kits of VCR mechanical parts like washers and
springs that come in handy. General belt or similar kits are not
worthwhile unless you are in the service business - there is too much
variety in the sizes and other characteristics of these types of parts
to make an assortment a good investment.
Note: while working with the top off, you may need to put pieces of
strategically located cardboard over the area of the cassette to block
extraneous light from causing erratic behavior (modes aborting, not
starting at all, etc.) with the start/end-of-tape sensors. Not all VCRs
are sensitive to extraneous illumination but I have been bitten more than
once by not doing this. Using overhead instead of direct illumination
will probably help as well. In extreme cases, placing electrical tape
over the end sensors may be needed but this will likely confuse the
microcontroller under certain conditions into thinking that a non-
existent tape is present - or if your troubleshooting will permit, leave
a cassette in the transport. (I have heard of at least one case where
this was a problem even for normal operation - apparently, light was
falling on the VCR in just the wrong way where it happened to be located.
The VCR would enter rewind mode regardless of what the helpless human
wanted unless tipped on end!)
A DMM or VOM is necessary for checking of power supply voltages and
testing of sensors, LEDs, switches, and other small components. Unless
you get deep into the electronic repair of VCRs, an oscilloscope is not
required.
There are two items of important test equipment that you probably already
have:
(From: someone who would prefer not to be identified).
Don't let this happen to you. Or, at least start out with an old expendable
VCR and accept the hits to your pride!
You can buy these for $6-12 but you can make one that is almost as nice:
These cheaters will load and 'play' just fine except that some machines
actually sense that the supply reel is being turned by the tape movement
during loading or always and will shut down if it isn't (among other
peculiarities) so you may have to do this by hand.
There are several benefits to using one of these, one of which is that
there is no chance of ruining a prized tape due to a hungry VCR. You will
also be able to feel the spindles to get an idea whether they are turning
properly and with enough torque in all modes. If you break out enough of
the top and bottom, you will have access to the idler and other under-cassette
parts at the same time. If you examine one of the commercial cassette
cheaters, you will see that very little is needed beyond the outer frame as
long as it sits properly on the indexing posts and doesn't jam the mechanism
when loading/ejecting.
For general video diagnosis including mechanical and tape eating problems,
a bunch of sacrificial tapes is handy - advertising, promos, feature shorts -
anything you do not care about but have been recorded on working VCRs.
Very often they get mangled and you do not want to continue to use mangled
tapes which may damage the VCR - in particular the video heads. However, once
you have the VCR basically working, you will want to test it start to finish
on a T120 cassette. This is because the reel hub size on those short
video cassettes is not the same as a standard (most commonly used) T120
cassette and may mask problems if the VCR is mechanically marginal in some
respects.
It is usually very easy to remove the top and bottom covers on VCRs.
For the top cover, there are usually some very obvious screws on the back
or sides, and in rare cases on the top. There may be a couple of screws
on the bottom as well that secure the top cover. For top loaders, you
will probably need to remove the cassette holder lid - there will be two
screws, perhaps hidden by rubber plugs.
Once all the screws are out, the top cover will lift up or slide back
and then come off easily. If it still does not want to budge, recheck
for screws you may have missed.
For the bottom cover, there are usually a half dozen or so screws around its
perimeter and sometimes in the middle as well. There may be one or two
grounding screws as well which are of different length and threads - these
should go back in the same location from where they came. Bottom covers
are usually simple sheet metal. In rare cases, you will need to remove
the front panel to free the bottom cover (or vice-versa).
Circuit boards may prevent access to the top or bottom of the tape
transport. Usually, removal of a few screws (often marked with red
paint or arrows on the circuit board) and perhaps pressing of a couple of
snaps will permit the board to be swung up on a hinge out of the way.
Front panels usually snap off, possibly requiring the removal of a few
screws on top or bottom.
Make notes of screw location and type and store the screws away in
a pill bottle, film canister, or ice cube tray.
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.
During servicing, a piece of opaque cardboard or other insulating material
should be placed above the cassette basket if any strange behavior is
detected that was not present with the cover in place. Not all VCRs are
particularly sensitive external illumination.
Do not be tempted to use compressed air!
I would quicker use a soft brush to carefully dust off the circuit boards and
power supply. Work in such a way that the resulting dust does not fall on
the mechanical parts.
For the deck itself, using compressed air could dislodge dirt and dust which
may then settle on lubricated parts contaminating them. High pressure air
could move oil or grease from where it is to where it should not be. If you
are talking about a shop air line, the pressure may be much much too high
and there may be contaminants as well.
A Q-tip (cotton swab) moistened with politically correct alcohol can be used
to remove dust and dirt from various surfaces of the deck (in addition to
the normal proper cleaning procedures for the guides, rollers, heads,
wheels, belts, etc.)
Try to locate the part with a bright light without moving the VCR. You may
have gotten lucky (yeah, right). Next, over an area where a dropped part
will be visible (not a shag carpet!), try any reasonable means to shake
it loose - upside down, a little gently tapping and shaking, etc. A hard
surface is better in some ways as you might hear the part drop. On the
other hand it may bounce into the great beyond.
If this does not work, you have two options:
To prevent this sort of thing from happening in the future you will no doubt
be much more careful. Sure you will! Some suggestions to prevent ejection
of an E-clip, split washer, or spring into the great beyond:
(From: Paul Sagi (kamrok@tm.net.my).)
For finding a small part dropped on the floor, I darken the room, then shine a
flashlight parallel to the floor, with the beam just touching the floor. the
oblique (if that is the correct word?) beam shows up the part (and any dirt if
the floor was not recently swept!) clearly. this works best on smooth floors
or short-pile carpets. on shag carpets, if the part is on top of the pile,
instead of having fallen into it (fat hope), the method works also. for shag
carpets where the part has tried to hide, shine the light downwards at right
angles and imagine how the part would look if seen against the background of
the carpet, to prime the mind to recognize it when seen. a strong magnet (for
steel parts like e-rings) can help when the above methods fail. sweeping or
vacuuming the carpet or floor, then sorting through the debris can also help,
especially for non-magnetic parts (sometimes cannot know if the part is
magnetic or not until after it is found!)
I do not agree with the advice that a small part that cannot be located often
can be left safely inside an electronic device. remember Murphy? he is
ever-vigilant and delights in ensuring the part will have fallen where it can
do harm when the power is switched on.
Please refer to the photo: Typical VHS VCR Tape
Transport Components or Sharp VCR Transport with
Major Parts Labeled for parts identification.
The following description applies to 99.9% of the VCRs in existence today.
I have seen one that had a sideways loading mechanism - very weird.
Looking at the unit from above with the front toward you:
Some VCRs use gears in place of rubber (as is the case with the VCR shown in
the photo: Typical VHS VCR Tape Transport
Components. Teeth can break off but these are generally quite reliable.
Some high-end decks may have separate motors for reel rotation.
Also on the same assembly are tilted metal guide posts - again
one for each side. These sometimes fall out with obvious consequences.
Proper functioning and adjustment of the roller guides is the most critical
requirement for proper tracking. (However, do not touch their settings
without being really sure that they are at fault and not until you have
read the sections relating to tape path alignment.) Clean and inspect.
A hard, shiny, dried out pinch roller can lead to tape edge munching and
erratic sound, speed, and tracking. Clean thoroughly. Inspect for cracked,
hard, shiny, or otherwise deteriorated rubber, and lack of free and smooth
rotation. Replace if any of these are present.
Even if you have no obvious record or playback symptoms, if the pinch roller
appears concave or with a distinct worn ridge, replacement is recommended -
erratic behavior will soon be the result. A tape which runs off center due
to a bad pinch roller may result in tape edge damage and over time can also
alter the wear pattern of the audio/control head and various guide posts.
A quick test of the pinch roller is to put the VCR into PLAY and *carefully*
try to stop it from turning between your thumb and forefinger - a good pinch
roller will not be easy to stop.
However, don't replace a pinch roller that is in good condition. The
replacement may be inferior. (Apparently for at least some JVC VCRs, the
original pinch roller is of very high quality and will last the life of
the VCR if cleaned properly.)
For additional information on replacement rubber parts, see the section:
Determining belt, tire, and pinch roller
specifications.
The cause for all of these is very often a bad idler tire or other dirty,
worn, or tired rubber parts. See the section below: "General guide to VCR
cleaning and rubber parts replacement". A VCR that just munched down your
favorite tape is very likely only in need of a little tender loving care.
WARNING: Don't turn a simple repair into a full length double feature. Most
tires and belts come off without extensive disassembly. However, if your VCR
is the exception, DO NOT remove anything to get at the rubber part that may be
part of a critical timing relationship - racks or gears, for example - before
fully understanding the implications of this action. In some cases, if a gear
is rotated even one tooth from where it should be, there can be unforeseen and
catastrophic consequences. See the section: Mechanical
relationships in VCRs for more information before proceeding any further!
Do not attempt to clean the video heads until you follow the proper
procedure given elsewhere in this document, you can break them - very
expensive lesson. In most cases, they do not need attention anyhow.
Q-tips and alcohol (91% medicinal is OK, pure isopropyl is better. Avoid
rubbing alcohol especially if it contains any additives) can be used
everywhere except the video heads. Just dry quickly to avoid leaving
residue behind or damaging the rubber parts further.
Cleaning may get your machine going well enough to get by until any replacement
rubber parts arrive and to confirm your diagnosis.
Things to clean:
Clean the pinch roller (presses against the capstan in Play, Record, and
Search mode CUE and REVIEW) and until no more black stuff comes off. Use
as many Q-tips as necessary until no more black gunk collects on Q-tip.
If the pinch roller is still hard, shiny or cracked, it will probably need
replacement. Many are available for about $6 from the sources listed
at the end of this document. It is sometimes possible to put the pinch
roller in an electric drill, drill press, or lathe, and carefully file off
the hard shiny dried out rubber surface layer, but only use a last
resort - and this fix is probably temporary at best. For a very detailed
and complete step-by-step procedure, search for "VCR crinkling tape, sound
fading, speed flipping" on
Google Groups.
(This is an archived sci.electronics.repair newsgroup posting.)
If the idler tire appears cracked, glazed, or dried out, it will need to be
replaced. About $.50 to $1.00. As a temporary measure, you can usually
turn the tire inside-out and replace it. The protected inner (now outer)
surface will grip well enough to restore functionality until a replacement
tire arrives - and verify the diagnosis as to the cause of your problem.
Also, the idler assembly includes a slip clutch. If this weakens, the
idler may not have enough force to press on the reel table edges. If it
becomes too tight, there may be audio, video, or crickled tape problems
and/or excess wear of the idler tire. When in doubt, the entire idler
assembly is often available as a replacement part. They can often be
disassembled and adjusted if necessary.
Make sure that there are no twists when a square cut belt or replacement
is installed on its pulleys.
On some models, you may need to unscrew circuit board(s) blocking access
to either the top or bottom of the tape transport. Make notes of what
went where - particularly different types of screws and routing of wires.
Any belts that appear loose, flabby or do not return instantly to
their relaxed size when stretched by 25% or so will need to be replaced
and may be the cause of your problems. Belts cost about $.30 to $2.00
and complete replacement belt kits are often available by model for $3. to
$12. Meanwhile, the belts will function better once they are cleaned,
maybe just enough to get by until your replacements arrive.
While VCRs should be cleaned periodically, the video heads themselves
usually do not need cleaning unless you have been playing old or defective
rental tapes which may leave oxide deposits on the tips of the delicate
ferrite head chips. Unless you are experiencing video snow, intermittent
color, or loss of or intermittent HiFi sound (HiFi VCRs only, the HiFi
heads are located on the video head drum and for the purposes of cleaning,
treated the same way) leave the video heads alone.
If you really feel that video head cleaning is needed, refer to the
sections on video head problem diagnosis and cleaning elsewhere in
this document.
I pride myself on the cleanings I do with all repairs, I like to keep my shop
up to command performance and a cut above the rest I usually even clean up the
chassis and deck of most equipment and relubricate and all the trim.
I have seen my share of broken heads come in from people after they use a
Q-tip...or a store bought cleaning tape...
I use a few different size hemostats with a folded up lint free cloth. When
folded, it really buffs the cylinder units and leaves a nice shine on the tape
guide rollers, and audio and erase heads too. I have cleaned a head with
chamois swabs and then gone over them with my own cloth and was horrified to
see the residue that was left from ordinary swabs, when it was all collected
on the cloth. It doesn't snag the video or stereo hi-fi heads either - I
have cleaned a few thousand this way and never snagged any
I use generation 2000 disk cleaner for heads and acetone to degrease the posts
and capstan - just a dip - not too much.
(Editor's note: take care with strong solvents like acetone - both to protect
your health and avoid damage to plastic parts. --- sam)
Pardon me while I trip over my long gray beard :-).
In the old days, we used to clean the platters in a disk drive using what were
essentially tongue depressors wrapped with a Texwipe (Lint-free paper). We
would first use 99% pure isopropyl alcohol and follow it with freon. (AAAAAh!
the Ozone layer!) We would then manually run the heads out over the platters
(while they were spinning) and listen for 'ticks'. If we heard any, we'd
repeat the process. For those who smoked in the computer room, the residue
could build up rather thick and evenly. Getting the whole mess off was a
chore. If such was the case, I actually would use Soap and water, followed by
water, then the alcohol and finally the freon. (This was more like R-22 and
not the R-12 variety. That, we used do dump into the atmosphere freely trying
to cool down components.)
I have resurrected many road-kill VCRs by using those cleaning techniques on
them. I haven't as yet had to use soap, but using other than alcohol proves
beneficial. Just don't get too liberal with any of the cleaning fluids. By
the way, the freon was used to remove any residue left behind by the alcohol.
NEVER, ever, use WD40 in a VCR! WD40 is not a good lubricant despite the
claims on the label. Legend has it that the WD stands for Water Displacer -
which is one of the functions of WD40 when used to coat tools. WD40 is much
too thin to do any good as a general lubricant and will quickly collect dirt
and dry up. It is also quite flammable and a pretty good solvent - and there
is no telling what will be affected by this:
(From: Matthew Fries (freeze@visi.com).)
A light machine oil like electric motor or sewing machine oil should be
used for gear or wheel shafts. A plastic safe grease like silicone grease
or Molylube is suitable for gear teeth, cams, and the roller guide tracks.
Unless the VCR was not properly lubricated at the factory (which is quite
possible), the only likely areas needing lubrication are the roller guide
tracks - clean and grease. Sometimes you will find a dry capstan, motor,
lever, or gear shaft but this is less likely.
In general, do not lubricate anything unless you know there is a need.
Never 'shotgun' a problem by lubricating everything in sight! You might
as well literally use a shotgun on the VCR!
For the following, do not go near the video head drum, only perform
demagnetization of the stationary A/C head, erase head, and guide
posts and rollers. In my opinion, the video heads should almost never
need to be demagnetized. The ferrite material from which they are
constructed is not prone to easily being magnetized like steel.
Use a small demagnetizer designed for a tape deck or cassette deck.
Do not use anything homemade that might be too powerful or a bulk
tape eraser which would certainly be too powerful.
Make sure the tip is covered with a soft material to prevent damage to
the finely polished surfaces in your VCR.
Turn power on to the demagnetizer when a couple of feet away from the VCR.
Then, slowly bring it in close and slowly go over all surfaces of anything
that the tape contacts or comes close to in the tape transport. The key
word here is **slowly**. Move fast, and you will make the magnetic
fields stronger. When finished, slowly draw the demagnetizer away to a
distance of a couple of feet before turning it off.
Use a large nail with its point filed down to a blunt tip covered with
tape or a plastic or rubber boot to protect the polished surfaces of the
heads. I have no idea of the exact number of turns but I'd say start with
100 turns of #20 to #26 AWG insulated wire. There should be a noticeable
vibration when bringing the tip with 1/4 inch or so of a ferrous surface
but not much beyond this.
CAUTION: This may be too strong for the video heads - stay away from them!
In fact, it may be too strong at the full 12 VAC. A lower voltage adapter
may be better or use on a Variac. If it pulls nails out of your drywall,
it's too strong. :) Use at your own risk!
(From: Steven L. Bender (buqu35d@prodigy.com).)
You need a Power Transformer about 3" in each direction, can be like a
low voltage 12 volt / 3 Amp unit or rated higher. Remove end bells if
any, remove all the metal laminations (break the first one, yank it,
and the rest will come easier). Re-insert all the metal laminations
facing in the same direction, with the "E" all pointed the same,
re-glue, varnish, or whatever. Connect AC Plug to the Primary, then
insulate the whole works with Plastic tape and outre layer of Duct
tape. After insulating it with several layers of tape - Instant Bulk
Eraser.
Warning - Do not apply power for more than 60 seconds at a time! (It will get
hot and burn your hand after two minutes.)
I had one of those for some years, but accidentally left it plugged in,
(pulled the wrong wire out of the 6 to 1 outlet box) and after a few
minutes, it smelled and was too hot to touch, and made a nasty noise as
the copper started to melt... (Sounds Effects of Liquid Krell Metal
in the distance...., Forbidden Planet - Paramount, 1956).
Luckily I didn't walk out, another few minutes and it would have caught fire..
I am not liable for any personal, profession, or consequential damages from
use of this information !!!
(From: Steve Walz (rstevew@armory.com).)
Use a transformer and remove the EI core pieces and replace all the E's
only in the same direction. Current limit it with a wire-wound resistor
so it doesn't overheat and put a momentary pushbutton on it and a power
cord to wall AC and insulate it so you don't shock yourself. Then place
it so the open face of the E core pieces faces the tape or disk or
whatever to be erased and push the button. Run it all over both sides of
the tape or disk and pull the tape or disk away before letting up on the
button if you wish to erase it. If you wish to magnetize a tool or such,
simply let up on the button while the object or tool is still in contact
with it. That's how that works! (You may have to do it a couple times before
you catch the AC cycle at the peak! --- Sam.)
(From: Pat Swayne (me@patswayne.com).)
Here's a safety tip for your homemade bulk tape eraser: Use a small length
of very thin solder as a fusable link. Place this as close to, but
insulated from, the primary windings as possible, and pass the current
through it. If the thing gets too hot, it will melt the solder and break
the connection.
(From: Sam.)
It would have to get mighty hot for that to be effective but it's cheap
enough. Of course, a thermal fuse or thermostat would be a more well
controlled alternative.
If attempting to load a cassette produces no response (though the
VCR has power), then there could be a problem with the microswitch that
senses the presence of a cassette, the cassette loading motor (if separate
from the main motor), a slipping or broken belt, or a faulty driver
or other electronic problem. Sometimes this could mean that the
microcontroller is confused due to a faulty mode switch or because
the mechanism somehow got into a peculiar state. Manual cycling of
the cassette loading mechanism might reset it. Gently push a cassette
in and turn the appropriate shaft or pulley by hand. First, try this with the
VCR unplugged. If nothing happens or you feel resistance, try the
other direction. Assuming you find no problems - there is no significant
resistance to your turning and the cassette basket cycles from fully
ejected to fully seated on the transport baseplate, leave the cassette
basket in a partially loaded position and plug the VCR into the AC power
and turn it on (this may not be necessary depending on the design of your VCR).
It should now reset itself and either load or eject the cassette.
If there are still no signs of a response, a power supply, motor, or
electronic problem is likely.
Note: If this only happens with T160 (8 hour) tapes, it may be a problem
with the thinner tape confusing the sensors. Avoiding these tapes is really
the best thing to do since they can cause all sorts of problems (especially
if they are an off-brand and of inferior quality to begin with).
If you hear a motor whirring but nothing happens, this is almost certainly a
slipping or broken belt or something blocking the proper movement a mechanical
part.
If pushing a cassette into the VCR results in it being ejected as though
it tasted really bad (there may or may not be hesitation), or if the cassette
cycles back and forth without stopping, there could be several possible
causes.
If it stops part way during loading, does it pause as though the motor
is straining or just abort with no warning? If the former, then check
carefully for foreign objects, or lack of lubrication. A typical cause
is a belt slipping, usually not the idler in this case. Help it out gently
and see if that will complete the cycle. Sometimes it is helpful to cycle
the mechanism by hand - turning the appropriate shaft or pulley and feeling
and watching for any place where it binds. If the basket moves in the wrong
way or you feel any significant resistance, try the other direction.
Sometimes, the sticky cassette labels partially or totally peal off and
clog the works. You may find a toy or rock inside carefully inserted by
your 3 year-old! A bit of the cassette shell might have broken off and
jammed the mechanism just to confuse you!
If the microcontroller were detecting an abnormality, then it would abort
instantly but would most likely try to unload the tape before giving up
but not in all designs. It is possible that if the expected behavior is
not produced by the end/beginning-of-tape sensors during cassette loading,
an abort could be initiated. Therefore, these sensors could be suspect.
In some cases, the mode switch may be dirty or faulty. A gear may have
broken some teeth or slipped a couple of teeth and the timing relationships
may be incorrect. There may be a microswitch that is controlled by the
cassette basket position and this may be defective or dirty.
Similarly, if the cassette seems to be cycling in and out in an apparently
infinite loop, there may be an obstruction or the microcontroller is confused
by a bad sensor or the basket is out of synchronization with the rest
of the mechanism. A squirt of contact cleaner into the microswitch sensor
and/or reflowing its bad solder connections may solve this type of problem.
Similar comments apply to cases where pressing the EJECT button
produces no response. In particular, if the cassette was loaded
successfully and you just finished a thoroughly enjoyable movie,
the microcontroller may think the mechanism is not safe and is not
ejecting to protect your valuable tape from possible damage should
it not be fully retracted into the cassette. As with loading, EJECT
may result in partial movement and shutdown or reloading the cassette
into the down position. All the same causes apply.
There are even some poorly designed VCRs where extraneous light through the
vent holes or tape door affect sensors and cause erratic operation. If a
bright light is shining on the VCR, block and see if anything changes!
To remedy the underlying problem, see the sections on: "Cassette loading
and eject problems" and other for appropriate information. This section
only deals with getting the cassette out without damaging either your
valuable recording or VCR.
Under no circumstances should you force anything - both your tape and your
VCR will be history.
First, see if the VCR just got into a confused state - pull the plug and
patiently wait a minute or two. This may reset the microcontroller and all
will be well. These things happen.
If this is not successful, you will need to open up the VCR (unplug it
first!) and attempt to cycle the mechanisms by hand. Probably both top and
bottom covers will need to be removed. The following procedures assume that
there are no broken parts, foreign objects, or other damage which might
prevent manual cycling of the tape loading and cassette loading mechanism.
(Inspect for toys and rocks.) Also note that some VCR designs use solenoids
to engage various operations. This will complicate your task (to put it
mildly) as locating and activating the proper ones at the appropriate time
is, well, a treat.
If a single motor performs both the tape loading and cassette loading
functions, stop turning as soon as you see the cassette start to rise
and read the next section before proceeding.
If you are not fully successful or if there is still a tape loop outside
the cassette even once you have been turning for what seems to be an
eternity, you can still try to eject the cassette but will need to be
extra careful not to crinkle the tape as the cassette door closes with
the tape sticking out. Before proceeding on in this case, try to find
a way to turn one of the reels to pull that tape back in as this will
make your task a lot easier. There may be an idler that swings between
the two reels and this may be accessible from the bottom (the cassette
will block it on top).
On a top loader, there is usually a solenoid specifically for EJECT or
a simple mechanical pushbutton. Once the appropriate lever is pressed,
the cassette should pop up - hold the basket with one hand as you do this
to prevent any exposed tape loop from being crinkled.
On a front loader, locate the cassette loading motor and begin turning
it in the appropriate direction - this will be fairly obvious assuming
there are no broken gear teeth or other broken parts and that something
isn't totally jammed. If this is the main capstan motor, then just
continue turning as in (1). Eventually the cassette should raise up
and out.
As above, applying external low voltage power (6 to 12 VDC) to the motor
*after* disconnecting it is an alternative if you cannot gain access to its
shaft to turn it by hand.
If you have a tape loop, be extra careful not to catch it on any
guideposts or obstructions as you remove the cassette. Then, wind it back
into the cassette by turning one of the reels (you may have to depress the
release button on the bottom of the cassette with a pencil - this is the
small hole in the center near the label side.)
And in some cases, just turning the VCR upside-down and gently easing the
cassette out will work. But as noted, don't force anything.
Assuming the tape is not torn and not badly crinkled, it should be fine.
If it is severely damaged, refer to the section:
Recovering damaged or broken tapes.
Assuming that the problem is still present, here are two suggestions:
If there is some underlying problem which caused the basket to be
lowered without a cassette in place, than the VCR may return to the
illegal state, do nothing, or do something else that is peculiar
once power is restored or any button is pressed.
For additional info on initialization problems, see the section:
VCR is failing the power-up sequence.
Anyway, rule out the idler tire as well as the idler clutch - if it
weakens, then the idler wheel does not press against the appropriate
reel with enough force to grip.
Is it s top or front loader? If a top loader, you should be able to
trick it into playing a nonexistent tape by covering up the end-of-tape
light (the one sticking up in the middle) so that it will think there is
a tape inserted. (In some models, there might also be a microswitch.)
This may permit you to see what is going on.
If a front loader, then it is tougher. You need a cassette cheater
(see the section: Cassette cheaters).
Then, with the cheater in place happily fooling the VCR, feel the
spindles while the machine is operating. In FF or REW, you may
find that they are not being driven or or being driven very weakly.
Try to determine if the idler is even being pushed into position or
is hung up on something.
If there is any chance that it is the idler tire, try turning it inside-out.
The relatively protected inner (now outer) surface may grip well enough to
confirm the diagnosis.
Has it been serviced in the last 15 years? The last 100 years?
Make sure the tape is not the problem - try another one.
If it starts the operation (as evidenced by whirring sounds and the tape
counter changing numbers) but at some point - perhaps near the end of
the tape - aborts and shuts down, then a worn idler tire, worn or broken
idler clutch, bad belt, or lubrication problem is likely. See the section:
VCR will not fast forward and/or rewind
as well as Lubrication of a VCR.
With instant start transports - where the tape is maintained around
the video head drum for all but the fastest rewind, there could be
other control problems as well.
If the tape starts fast forwarding or rewinding properly (from a visual
inspection with the cover off) but the tape counter does not change value
and then the unit shuts down, a reel rotation sensor problem is likely.
See the section: Reel rotation sensors.
If the operation aborts at the same location on only certain tapes, there
could be pinholes in the tape oxide coating allowing light to pass through
and confuse the sensors. This happens mostly with T160 or old well worn
tapes. If you can locate the problem area, you can try indelible ink on the
NON-oxide side of the tape but DO NOT use adhesive tape or glue. Else,
discard the tape or live with its behavior.
First confirm that the same thing happens with more than one cassette - it
could be defective.
(Portions from: Alan McKinnon (alan.mck@pixie.co.za) and Oldguyteck
(edward.croteau@the-spa.com).)
You get several types of noisy rewind:
All Rights Reserved
2. There is no charge except to cover the costs of copying.
DISCLAIMER
Working on VCRs entails a number of personal risks:
electrical, mechanical, as well as the possibility of irreversible
damage to the equipment and loss of irreplaceable recordings due to improper
repair or adjustment.
Introduction
Entertainment - then and now
Think back past 25 years. You went to the theater to see a movie. You watched
TV programs when they were broadcast (there was no cable, remember?) or you
missed them. TV studios and industry had video recording equipment but it was
expensive and cumbersome. Little did you realize at the time, but after
some false starts, the modern video revolution was about to be born. Are
we better off? Whatever you decide, there is no going back. You may be able
to leave your VCR's clock flashing 12:00 but you cannot escape the impact
that this technology has had on so many aspects of your life.
Scope of this document
This document was developed specifically for the troubleshooting and repair
of VCRs using the VHS format. However, most of it also applies to
Beta, 8 mm, 4 mm (DAT), and the industrial U-Matic formats as well. The
basic tape related problems found in camcorders are also likely to be similar
to those for full size VCRs. However, due to the miniaturization and
difficulty in accessing internal parts of these units, troubleshooting and
repair are generally much more difficult.
VCR repair
Note: for VCR emergencies that just cannot wait, the solution may be found
in the document: VCR First Aid and you may not need
to read further. VCR First Aid deals with the half
dozen or so acute VCR problems that may tempt you to throw something through
the window - or worse.
Repair or replace
While VCRs with new convenience features are constantly introduced, the
basic function of playing a tape has not changed significantly in 25 years.
Even the introduction of HQ about 15 years ago does not represent a dramatic
improvement. Therefore, unless you really do need a quick start transport,
a real-time counter, index search, or the like, repair may not be a bad
idea. The older VCRs are built much more solidly than the $100 models of
today. Even high-end VCRs may be built around a poorly designed transport
and flimsy chassis. Many older VCRs - for example 10 year old Panasonic
models (and their clones) can be kept functional - nearly indefinitely,
it would seem - at minimal cost. The consensus of those in the business is
generally that most newer VCRs are built to last through the warranty and then
either be too expensive to repair or simply impossible to repair. However,
there are still millions of middle age to older VCRs out there whose life
could be greatly extended with a little tender loving care. If you buy a $79
K-Mart special, you get what you pay for. Don't expect it to last more than a
year or so. However, if you have something that is a few years old, it may be
well worth the effort to keep it going. As already noted, newer VCRs don't
have significant picture or sound quality - they are just more cheaply made
to optimize the manufacturer's bottom line.
Video Recording Technology
Helical scan video recording
Modern VCRs - both consumer and professional - are based on what is known
as helical scan recording. The main technological challenge that confronted
the designers of early video recording machines was achieving the necessary
bandwidth - several MHz - to faithfully capture the high frequency video
signal. The first such machines ran normal audio tape past stationary
recording heads at high speed - 10s of feet per second - in an attempt
to solve this problem. Needless to say, the mechanisms were complex,
a finite length of tape could only record a few minutes of video, and the
heads wore out almost as quickly. If anything - anything at all - went
wrong with the tape transport, you were up to your eyeballs is spilled
tape. An alternative technology was clearly needed.
VHS video
Most of the following discussion unless otherwise noted applies to the VHS
format. Beta, which preceded VHS into the marketplace and which has all
but disappeared for consumer VCRs is actually a somewhat better system
technologically with superior picture quality. Physical tape format is
similar to VHS but differs in the details. However, Sony's licensing
practices with respect to Beta made it inevitable that VHS would triumph
in the marketplace. Too bad in some ways. The 8 mm format, used mostly
used nowadays in camcorders, is also helical scan but there are no separate
audio and control tracks - they are part of the video track.
VHS audio
Sound for the VHS format is not merged into the video signal on the tape.
For non-HiFi VHS VCRs, a separate stationary tape head is responsible for
the audio signal. Due to the very slow tape speed, audio quality is not
even comparable to a cheap audio cassette player even at the SP speed. VHS
HiFi overcomes this by FM recording of the audio signal deep in the tape
(recorded by a separate set of HiFi heads just before the video information),
actually buried under the video information. The left and right audio
channels are recorded in separate frequency bands - centered around 1.3 and
1.7 Mhz respectively. The azimuth angles for the HiFi audio heads are +/- 30
degrees which minimizes crosstalk between the recorded HiFi audio and video
information.
Beta and 8 mm audio
Like VHS, Beta has both linear and HiFi audio but in that system, the HiFi
audio signal is actually recorded and played back via the video heads and
uses a portion of the frequency spectrum to fit it in with the video
information.
More information on video formats
See the following for additional information on these and other video formats.
VCR servo systems
Linear tape motion and head drum rotation must be precisely synchronized
during record, play, and special effects play modes. The general functioning
is similar for all but the source of the basic reference signal differs for
play and record. Some of the specific relationships may differ depending
on the specific VCR design.
Video special effects
For CUE (fast play forward) and REV (fast play reverse), the capstan speed
is phase locked to a multiple of the control track. Since the video heads
are crossing multiple tracks during these modes, some noise bars are
unavoidable. At SP speed, special wide or dual azimuth heads are required
to minimize this degradation. Thus, only 4 head VCRs can play SP tapes at
fast speeds with minimal noise. With EP speed, the tracks actually overlap
and a normal video head is wide enough to pick up enough signal from adjacent
tracks to produce a mostly noise free picture. Due to the way adjacent tracks
line up with LP speed, most of these special effects cannot be used
due to serious tearing of the picture. The sophisticated processing
needed for proper support at LP speed is generally not included in modern VCRs
due to the apparent lack of interest in the LP speed (recording support at LP
speed seems to be absent in more and more newer VCRs though they will all
play back LP tapes at normal playback speed).
For more information on VCR and related technology
The books listed in the section: Popular books on VCR
maintenance and repair include additional information on the theory and
implementation of the technology of video recording and VCRs.
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 site to rival this one - but WITH a tech-tips database and nice graphics
Check out:
VCR Placement, Preventive Maintenance, and Rental Tapes
General VCR placement considerations
Proper care of a VCR does not require much. Following the recommendations
below will assure long life and minimize repairs.
Video tape quality
"What are the 'good' and 'bad' brands of videotapes (T-120)? Are the 'extra'
or "high" grades really better?"
How long do video tapes last?
(From: Raymond Carlsen (rrcc@u.washington.edu).)
Preventive maintenance
You no doubt have heard that a VCR should be cleaned and checked periodically.
This is basically good advice but few people actually do follow it. I cannot
give a specific schedule to follow as many factors influence the amount of
wear and tear on your VCR:
Sample VCR preventive maintenance schedule
Here is an example of the recommended inspection, lubrication, and
replacement schedule for a typical VCR as provided by the manufacturer.
This is from the Sams VCRfact for a particular non-HiFi RCA VCR. I am
providing this for information only and am not necessarily recommending
these or other similar hard and fast rules for VCR preventive maintenance.
After What to do Which parts
------------------------------------------------------------------------------
250 tapes Clean A/C head, capstan, erase head, pinch roller,
impedance roller, supply reel table, takeup
reel table, video heads.
500 tapes Replace Video heads (upper cylinder).
750 tapes Replace Pinch roller
1000 tapes Grease Loading cam gears, impedance roller shaft,
roller guide tracks.
Oil Supply reel shaft, takeup reel shaft.
Replace Reel belt, loading motor belt, main brake
spring, main brake arms (left and right).
2000 tapes Replace A/C head, erase head, supply reel table,
takeup reel table.
2500 tapes Replace Cylinder unit.
Rental tape considerations
It would be nice for your VCR if rental movies had never been invented.
You have no idea of the history of any tape you bring home. The following
may also apply to tapes in your video library or tapes given to you by
friends or relatives:
Air purifiers and rubber parts
Some types of electronic air purifiers may accelerate the deterioration
of certain types of rubber materials in electronic equipment as well as
household items like carpet pads and door seals. There are also issues
with respect to claimed health benefits as well as adverse health effects
but that discussion is for a different forum.
VCR Maintenance and Troubleshooting Guide
Safety
Once you remove the cover(s) of a VCR (ignoring the warnings about no user
serviceable parts, etc.), there are some risks to you and your VCR.
You also, of course, void the warranty (at least in principle). Therefore,
if the unit is still under warranty, having it serviced professionally may
be your wisest option.
Troubleshooting tips
Many problems have simple solutions. Don't immediately assume that
your problem is some combination of esoteric complex convoluted
failures. For a VCR, it may just be a bad belt or an experiment in rock
placement by your 3-year old. Try to remember that the problems with the
most catastrophic impact on operation (a VCR that eats tapes) usually
have the simplest solutions (replace the idler tire). The kind of problems
we would like to avoid at all costs are the ones that are intermittent
or difficult to reproduce: the occasional interference or a VCR that
sometimes will not record your favorite soaps on alternate Thursdays
before a full moon.
Test equipment
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 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.
Why you should read the entire FAQ first
If you have no prior experience with precision electromechanical repair,
don't just jump in as the following actual experience demonstrates:
"Ok, I did something dumb. I was given an old VCR (early 80s) a couple
weeks ago (JVC-7100U). It stopped playing and recording, but FF and
rewind worked fine. Reading the FAQ, I decided to check it out. I took
the top off, and was trying to make the motor run so I could see the
problem. There was an incandescent light, and I figured there was
a light sensor, so I moved the lamp out of the way. The FAQ suggests
electrical tape over the lamp, but I hadn't read it yet. My manipulation
caused the lamp to fail. Until I could replace it, I just jumped the
connection, which worked fine for awhile. I had just figured out the
problem with play/record was a drive wheel not making contact with
the take-up reel. It seemed to be a result of a weak spring, and I
was trying to figure out which one, when the screwdriver I was
manipulating the arm with slipped, and contacted the back side of
a circuit board. Lesson number two: Use a chopstick for that purpose.
I believe it was at this point I realized I got no reaction from
any of the VCR control buttons, so maybe I shorted something out. All
the buttons worked before. Even worse, as I was reinstalling the
tape loading mechanism, the screwdriver slipped again, in a different
place, and I did see a flash when it contacted the back of the circuit
board. Whoops."
Cassette cheaters
When troubleshooting mechanical problems in a VCR, one of the handiest
accessories is a cassette cheater - a frame to fool the VCR into thinking
there is a cassette in place so that you have access to the reel spindles
and idler.
Test tapes
When aligning the tape path, a test tape will be needed as a reference.
Actually, you want two - one recorded at the SP (2 hour) speed and another
recorded at the EP (6 hour) speed. These do not need to be exorbitantly
priced professional alignment tapes. A couple of recordings made on
a known working VCR will get you close enough for most purposes.
Do not use these same tapes for diagnosing or testing of mechanical problems,
your VCR may be hungry and they may get eaten.
Getting inside a VCR
You will void the warranty - at least in principle. There are usually no
warranty seals on a VCR so unless you cause visible damage or mangle the
screws, it is unlikely that this would be detected. You need to decide.
A VCR still under warranty should probably be returned for warranty
service for any covered problems except those with the most obvious
and easy solutions.
Why does my VCR shut down or behave strangely when I remove the cover?
There are various sensors in a VCR that are light sensitive - it is not
a safety interlock (though it acts this way in some VCRs) but a result
of the way the tape start and end sensors operate. VHS tapes
have a clear leader and trailer. An LED or light bulb poking up near
the center of the cassette shine towards sensors at either side of the
cassette. When light is detected the VCR assumes that it is at the
appropriate end of the tape and shuts off (or rewinds if in PLAY mode
when it senses the end depending on model).
Getting built up dust and dirt out of a VCR
This should be the first step in any inspection and cleaning procedure.
What to do if a tiny tiny part falls into the VCR
We have all done this: a tiny washer or spring pops off and disappears from
sight inside the guts of the unit. Don't panic. First - unplug the VCR if it
is plugged into the AC. Remove the battery pack from a camcorder.
VCR Tape Transport Fundamentals
Parts of the tape transport in a VCR
Thanks to Brian Siler (bsiler@bigfoot.com) for using his Snappy(tm) rig to
capture some of these original photos.
Alex's quick tips
(From Alex (ramjam@globalserve.net).)
Most common problems
General guide to VCR cleaning and rubber parts replacement
All the guideposts, wheels, and rubber parts of a VCR should be cleaned
periodically - how often depends on usage. Of course, no one really does it
unless something goes wrong.
Polishing your tape path
(From: Gillraker (eternity@mcp.cybertron.com).)
Tom's comments on approaches to cleaning
(From: Thomas L DeTogne (tdetogne@home.com).)
Lubrication of a VCR
The short recommendation is: Don't add any oil or grease unless you
are positively sure it is needed. Most parts in a VCR are lubricated
at the factory and do not need any further lubrication over their lifetime.
Too much lubrication is worse then too little. It is easy to add a drop
of oil but difficult and time consuming to restore a VCR that has taken a swim.
"I heard a horror story when I was in tech school about someone who heard a
little squeaking inside the VCR when it was in PLAY mode, so he sprayed WD40
in through the tape door (front loading) and 'lubricated' the entire inside
of the VCR. The students who were working on this took apart the entire
mechanism, sprayed it clean with TF solvent (4 cans - there goes the ozone)
and it still didn't work. No surprise."
Head demagnetizing
With audio tape decks, demagnetizing is often recommended to improve
sound quality and frequency response. There is some debate as to
how much benefit there is to this practice but if done properly,
there is little risk. Demagnetizing removes the residual magnetic
fields that can build up on ferrous parts of the tape heads and
various guideposts and other parts in the tape path which may affect
frequency response.
Homemade VCR head demagnetizer
Rather than trying to build something that plugs directly into the AC line,
use an *AC* wall adapter. Typically something from an old modem with a rating
of around 1 A at 12 VAC should be fine. There is no significant safety
hazard to touch connections with power on and they are short circuit
protected so no matter what you do, there will be no immediate damage
to the adapter.
Building a bulk tape eraser
A variety of approaches work for this - all based on strong magnetic fields.
These will erase floppy diskettes, audio and video tapes, and all your credit
cards and Turnpike passes!
Cassette and Tape Loading Problems
Cassette loading and eject problems
Cassette loading places the cassette into proper position on the tape
transport. In a front loader, pushing the cassette gently into the
slot should cause a motor to take over and suck it in and down to rest
on indexing pins. The mechanism that actually holds the cassette is called
the cassette basket. Several types of problems are possible: the VCR may
ignore you when you push the cassette in or press EJECT, or it may
spit it out immediately or cycle back and forth. On a top loader, you do
most of the cassette loading manually, so the only likely problem will be
if EJECT does not work.
Ejecting a cassette from an uncooperative VCR
It is a common experience - the rental movie is due back at the video
store **now** but no matter how you press the EJECT button, yell, scream,
hold your breath, or jump up and down, the cassette refuses to be appear.
VCR is confused - will not eject non-existent tape
If for some reason, the microcontroller gets confused and refuses to raise
the basket and there is no tape in the VCR, first, try pulling the plug
for a minute or two. This may reset the error condition. However, since
the mechanism is in an illegal state, the microcontroller may refuse to do
anything for fear of making things worse.
Fast Forward and Rewind Problems
VCR will not fast forward and/or rewind
Usually, the owner will admit that the machine is pre-Jurassic and
has never been cleaned or serviced.
VCR aborts fast forward or rewind
In this case, the tape starts to move - possibly at a reasonable speed -
but then may shut down - possibly erratic or tape dependent.
Noisy REW or FF
While these operations are never exactly quiet, when grinding or squeaking
noises are evident, it is time to at least consider the possibilities.
