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-   -   Zenith Avante Issue (http://www.videokarma.org/showthread.php?t=270081)

TinCanAlley 02-01-2018 11:49 PM

Zenith Avante Issue
 
Okay, I don't know exactly how to describe this current problem. I'm sure I can fix it once I know where to look. I believe it to be somewhere in the horizontal circuits.

Most time now, when I turn on the set, there is instability in the image. It's like parts of the image are being pulled inward ever so slightly and then back out. I heard someone say something about horizontal pulling, but I couldn't find anything about it. Sometimes it does it on first use, but most time it starts after about 30 or more minutes of use.

I've tried to capture it a few times, but each time it stopped. Then started up again after I put the camera away. It's like it knows.

I'm certain it could be as simple as reseating something as a good smack on the side can make the image move.

Also, where would one look for fluctuations in contrast? Not too often, but often enough, I'm watching something and the entire screen will get darker and them go back. Could do it just once, or do it multiple times.

Overall, it's a great set. Just want to track down the last two issues.

Thanks

zeno 02-02-2018 07:54 AM

Which chassis ??
On all chassii if they have plug in transistors solder them in.
Also check the 330 ohm resistor on horz module, 9-57 or 9-90
Be sure all the safety caps are the new orange ones.
Check the 1.5 ( IIRC ) ohm resistor at base of hoz out transistor.
For brite issue on uprights check the 9-88 & 9-89 for PC cons
under the white resistor packs IF it uses them.
On flat chassis the ends of the terminal strips often make grounds,
be sure they are not breaking free.
Chromatic switches get noisy also.
That will keep you busy !

73 Zeno :smoke:
LFOD !

TinCanAlley 02-02-2018 12:33 PM

1 Attachment(s)
25EC58

The thing has many plug in transistors, that's for sure.
Updated all the safety caps few years back.

Electronic M 02-02-2018 02:01 PM

If the pull in moves vertically change the PS filter caps. The contrast issue could also be intermittent video output transistors...I had that with the RGB outputs.

TinCanAlley 02-02-2018 05:34 PM

Quote:

Originally Posted by Electronic M (Post 3195681)
If the pull in moves vertically change the PS filter caps. The contrast issue could also be intermittent video output transistors...I had that with the RGB outputs.

It pulls in from the sides, so horizontally. It is more of a twitch and doesn't pull in so far that you see black long the edge of the CRT. I really have to capture it on video. I think I will setup a cam tomorrow and see if I can capture it.

Electronic M 02-02-2018 06:53 PM

Quote:

Originally Posted by TinCanAlley (Post 3195683)
It pulls in from the sides, so horizontally. It is more of a twitch and doesn't pull in so far that you see black long the edge of the CRT. I really have to capture it on video. I think I will setup a cam tomorrow and see if I can capture it.

I know it pulls in horizontally! What I meant is if the horizontal pull in also moves vertically (ie what should be a straight fence post on screen has a wave running down it's side) then it is an electrolytic problem.

TinCanAlley 02-03-2018 12:05 AM

Quote:

Originally Posted by Electronic M (Post 3195685)
I know it pulls in horizontally! What I meant is if the horizontal pull in also moves vertically (ie what should be a straight fence post on screen has a wave running down it's side) then it is an electrolytic problem.

Okay, I think I understand. If there was a fence post standing vertically, then when it happens, it wouldn't be visible on the edge of the post for the entire length of the post. So when the pull happens, it is at random points on the screen edge. I hope I'm getting this right. More reason for me to capture it on video.

TinCanAlley 03-05-2018 12:57 AM

Okay, I finally caught it while recording. I have slowed it down 50% so you get a better view of what is happening. Hopefully this will be enough to identify the circuit I need to look over.

https://youtu.be/KtdCMtVamjs

DavGoodlin 03-06-2018 10:53 AM

That was a good capture. Was the video source a paused VHS tape? The 9-57 horizontal osc module was susceptible to flag-waving at the top of the raster with many VCR's.

The cure from PTS and Zenith-OEM among others was a 9-57 VCR, which was an empty 9-57 pcb used as a plug for the CC-II H-osc, 9-90 module on top.

This looks like a video or sync lock issue instead of sweep. Look at the video detector sync pulse with a scope and you could see that twitch.

zeno 03-06-2018 11:50 AM

If you have a scope & generator that would help.
Easy to try is AGC delay. Turn it till snow JUST goes away.
Next I would get rid of the sockets on the 9-57. They caused
more problems than the transistors.

73 Zeno:smoke:
LFOD !

TinCanAlley 03-06-2018 01:09 PM

Quote:

Originally Posted by DavGoodlin (Post 3196990)
That was a good capture. Was the video source a paused VHS tape? The 9-57 horizontal osc module was susceptible to flag-waving at the top of the raster with many VCR's.

The cure from PTS and Zenith-OEM among others was a 9-57 VCR, which was an empty 9-57 pcb used as a plug for the CC-II H-osc, 9-90 module on top.

This looks like a video or sync lock issue instead of sweep. Look at the video detector sync pulse with a scope and you could see that twitch.

Not a VHS. It's a paused DVD. When it started acting up, I paused it and recorded.

TinCanAlley 03-06-2018 01:12 PM

Quote:

Originally Posted by zeno (Post 3196993)
If you have a scope & generator that would help.
Easy to try is AGC delay. Turn it till snow JUST goes away.
Next I would get rid of the sockets on the 9-57. They caused
more problems than the transistors.

73 Zeno:smoke:
LFOD !

I have both those tools.

I will try adjusting the AGC. Is that something that can change? I remember adjusting it a few years ago when I was updating modules.

As for the 9-57... Get rid of sockets?

Thanks

TinCanAlley 03-06-2018 01:18 PM

1 Attachment(s)
Quote:

Originally Posted by zeno (Post 3196993)
If you have a scope & generator that would help.
Easy to try is AGC delay. Turn it till snow JUST goes away.
Next I would get rid of the sockets on the 9-57. They caused
more problems than the transistors.

73 Zeno:smoke:
LFOD !

This is the 9-57.

zeno 03-06-2018 07:47 PM

OK thats an updated module. Original ones had plug in
transistors.

TinCanAlley 03-06-2018 10:37 PM

Quote:

Originally Posted by zeno (Post 3197016)
OK thats an updated module. Original ones had plug in
transistors.

Oh, this one has plug in transistors. Should I pull them and reseat? I can go the soldering route if there's an absolute need for it. The chassis has quite a number of plug-in transistors.


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