Zenith Avante Issue

[DavGoodlin]

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]

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
LFOD !

[TinCanAlley]

Originally Posted by zeno

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
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]

Originally Posted by zeno

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
LFOD !

This is the 9-57.

[zeno]

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

[TinCanAlley]

Originally Posted by zeno

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.

[zeno]

Can barely see them. Anyhows solder them in. Looks H sweep
for sure, dont think its PS. Hang scope on H drive & see if
it is there. Generator is just for a constant pix.

73 Zeno
LFOD !

[TinCanAlley]

Okay, so I am only now getting around to taking out the horizontal board and soldering the transistors into their mounts in hopes of getting rid of the unstable horizontal.

But before I do, I really think I'm onto something in trying to fix the jailbar problem. I've put it back on the scope and see solid ringing in the brightness limiter circuit. I also noticed that under normal blacks or dark screens, the jailbars are most visible. If the image goes to a deep black, think blacker than black, they disappear. I've noticed this on all material when the background goes to a deep black. I'm assuming this might have something to do with the brightness limiter. What do you think? If it is a possibility, can I upload that section of the schematics and get help identifying parts of the circuit to test/replace?

thanks

[TinCanAlley]

Originally Posted by DavGoodlin

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.