(From: David Kuhajda (firstname.lastname@example.org).)
|NotTaR of Television Sets : No video on late model Sony TVs
1994-2007, Samuel M. Goldwasser. 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.
I may be contacted via the Sci.Electronics.Repair FAQ (www.repairfaq.org) Email Links Page.
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This following assumes that the more basic TV troubleshooting has already
been performed and resulted in no solution - i.e., filaments are lit up,
CRT voltages are all correct but the cathodes are all in cutoff, main power
supply voltages are present, etc
The 3 most common causes of no video, but good audio are as follows:
- AKB blanking due to either a fault in the AKB circuit or the CRT has
one gun that is too weak and the AKB won't unblank the CRT.
- Loss of vertical deflection. The system control must see the vertical
return pulse to unblank the video.
- Loss of data bus communication with the Jungle IC. The Jungle IC must
send the all OK signal to the micro before it will unblank the video.
- Try changing the volume with the volume control. If it changes the
data bus is not the problem. This is assuming the TV is tuned to a good TV
- Mark the EXACT position of the screen/G2 control with a marker. Then
turn the G2 control up.
- If the picture unblanks and a gray scale bar pattern is used, you can
usually see which CRT gun is weak. Time to replace the CRT for a long term
fix. All of the temporary fixes I have tried resulted in only a few months
extra life out of the tube.
- If the picture does not unblank and it looks kind of like there is a
halo near the top of the screen. The vertical circuit needs checked for
proper operation and repaired. WARNING do not continue to operate the TV
set in this mode for any length of time, it will crack the CRT from
localized heating!!!! (because the guns are shooting into the extreme top
of the tube and possible the neck of the tube)
RETURN the G2 control to the exact position that was marked before you
The typical failure mode of the vertical circuit in a Sony causes only
one of the vertical supply resistors to open usually. Either the +15 V or
-15 V. This puts a full + or -15 V on the yoke which deflects the guns into
the glass envelope of the tube.
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| Various video standards>>