View Full Version : what do you think? strange zenith symptom on 20Y1C38 chassis


drh4683
09-04-2007, 08:45 PM
Im a bit stumped on this one. Perhaps is nothing to be concerned about at all. I try to have my TV's 100% working correct, even small problems annoy me.

This 20Y1C38 zenith has a rather unique symptom which I've never seen before. Im getting these retrace lines on the screen, but only if I advance the AGC control too far (once the screen begins to overload). Once I back off, they just go away all together. If I advance the AGC all the way to black, I still get these retrace lines, but they are not consistently spaced and tend to jump around.

At first, I thought it was some of this closed caption info comming across the screen, but I get this consistent pattern on all channels.

I checked out both germanium blanking diodes and damper tube of course. Your obvious tests have been performed and voltages are very close to normal on the AGC and Y circuits.

I can only make scope measurements with no signal to compare with the schematics, yet with no signal everything is fine. If the AGC is backed off to appropriate level, not a trace (pun) of retrace is visable, which I guess is a good thing.

In the photos you can see what this looks like. For the sake of getting good photos, the contrast is cranked to near max, brightness lowered a bit and AGC into overload. Color level turned all the way down.

The last picture is how the set works when the AGC is backed off of overload which is how it should be adjusted and has a great picture.

What do you think?

Findm-Keepm
09-04-2007, 10:56 PM
The last picture is how the set works when the AGC is backed off of overload which is how it should be adjusted and has a great picture.

What do you think?

Keyed AGC bringing in some of the "key" when in overload? I dunno....:scratch2:

The last picture looks great, except the Cubbies are losing.....:sigh:

Cheers,

mr_fixer
09-05-2007, 01:41 AM
The really weird thing that i noticed is that the retrace is 3 separate colors, RBG. like the retrace is modulating the color detector? or convergence? Its been a long long time since i looked over color tv schematics. Logan

Jeffhs
09-07-2007, 11:33 PM
If the set shows a normal picture without retrace lines when the AGC is set where it should be (as yours obviously does), I wouldn't worry about what the pic looks like when the control is set anywhere else.

RaymondLeggs
09-08-2007, 04:03 PM
What does that mean if the entire CRT sinks into the front of the TV

RaymondLeggs
09-11-2007, 04:50 PM
I guess I'll never know..

drh4683
09-11-2007, 06:28 PM
I have no idea, ive never used or heard of the term.

RaymondLeggs
09-11-2007, 07:34 PM
I have no idea, ive never used or heard of the term.

Well it looks like the CRT has slid off Its mount on one side causing it to cave in a bit I hope the CRT neck is intact.. If i could only get somone to move it out of the house and plug it in..:D

Maybe it will catch fire! :lmao: :eek: :yikes: