Zenith jumpy picture ...

[rwagoner]

I have an old Zenith Advanced System 3 console from about 1990 or so. Picture is still beautiful, so I hate to dump it. Got a Firestick and an HDMI to AV converter to get DirecTV Stream to it ... kind of works but I get the jumpy picture that was fairly well-known with some game consoles (etc).

It seems there used to be a modification that could be made to one of the boards to stop this problem (I remember a tech telling me about it). Does anyone happen to remember what it was and how to do it? Or are there HDMI-AV converters that work better?

Here's an oddity - if I plug the video output from the AV converter to the AV Loop Output video connection (instead of the normal AV video input, leaving the audio cables in the input), the picture doesn't jump (or RARELY does) and the video is MUCH brighter. Actually looks great when I adjust the black level WAY down.If nothing else would it hurt the TV to connect it this way? Anyone known why it is brighter?

[old_tv_nut]

It seems odd that it's jumpy on the HDMI to AV converter, which *ought* to have standard NTSC scan rates and sync. But maybe it doesn't. Does anyone here know for sure?

Regarding the bright pic going into the loop through, this is probably because it expects to have a 75 ohm termination, and you are not terminating it, resulting in twice-normal video level.

[rwagoner]

Originally Posted by old_tv_nut

It seems odd that it's jumpy on the HDMI to AV converter, which *ought* to have standard NTSC scan rates and sync. But maybe it doesn't. Does anyone here know for sure?

Regarding the bright pic going into the loop through, this is probably because it expects to have a 75 ohm termination, and you are not terminating it, resulting in twice-normal video level.

There was a known issue with Zenith TVs of the era and something "confuses" the sync system (probably not a great description but that's my memory of the issue). Apparently game console companies had a fix they provided free but it was at the game console level, not the TV. And it happens with AV inputs OR antenna inputs.

[old_tv_nut]

The game console problem was due to the games using non-NTSC-standard scan rates (often 262 line/60 progressive) along with non-standard sync waveforms. Zenith had just introduced a sync detection/count-down chip that looked for the full NTSC vertical sync pattern and locked so well on over-the-air signals that the signal could be so weak that you couldn't recognize the picture, yet the vertical and horizontal were perfectly stable and no hold controls were required. They had to modify the design to detect non-standard sync and default back to separate H and V detection in that case.

I don't remember if there was a fix *in the TV* for these earliest chipsets with countdown or not.

Here's a previous thread that said the game makers offered a fix, but also mentions some TVs with a jumper that could be changed:
http://videokarma.org/showthread.php...h+sync+problem

[dishdude]

By 1990 this issue was fixed, I'd try a different converter. These HDMI to A/V converters vary by quality a lot.

[Electronic M]

This would be expensive as heck, but you could try my HDMI conversion solution. Get a ~$250 used HDMI to HD ATSC RF modulator and a DTV converter box. The TV should sync properly with the DTV converter box (if it doesn't the TV it's self is broken). Benefits include the TV being able to tune DTV with the converter box, on a 16x9 HDMI source being able to choose between letter box or a full screen crop of the center of the 16x9 image, and being able to move the TV to another room and recieving the HDMI to ATSC converter without wires connecting them (assuming you pick an ATSC modulator with more than 40dBmV output and hook a good UHF antenna to it's output, and a second antenna to the DTV box).

I had a different primary reason for buying the ATSC modulator but the aspect ratio conversion came in a close second and works better than anything else I've used to convert HDMI to NTSC.

[rwagoner]

Tried a different HDMI to AV converter ... and it acts the same way. I am thinking that it is something going off-spec in the TV, as the old converter DID work OK (occasional "jumps" but not like now) and over the past few months it suddenly got worse.

For now running the video input "backwards" (with the black level and contrast turned way down) works OK -- only jumpy on really bright video, and the TV itself using a VCR, DVD or even a DTV converter box gives a solid stable picture.

The only reason I don't run a DTV converter all the time is that I am too lazy to run an antenna wire to the room, and those inside antennas are terrible.

Why do I keep the TV? Not really sure. My wife and I got it as a wedding gift to ourselves when we got engaged back in 1990. Still has a beautiful picture. Absolutely not practical to keep ...

[rwagoner]

OK - forget everything I wrote - I connected the DVD/VCR and IT is jumpy too. I thought it was not but I didn't watch it enough. Perhaps a bad component on the input board? It does it on the AV input AND the RF antenna input. But when I connected the Zenith digital converter box to either, it was stable.

It is not jumpy like the vertical hold it off. It is "faster" if that makes sense. And sometimes an odd horizontal shift at the top and middle of the picture. I can post a video if it would help. Or should I just give it up?

And it still works fine most of the time when connecting the video input to the TV to the output loop.

[rwagoner]

In case it helps, it uses the 9-959 main and 9-754 sweep boards. I have not taken out either, but did not see any obvious bulging or leaking capacitors.

When I was playing with the menus, I did note that one of the menu lines was not stable when it was on and the picture was acting up.

[rwagoner]

Sorry to keep posting so much, but I keep noticing different things that might help diagnose it. For example, just now I had unplugged it for a while and tried it out and the condition has definitely gotten worse, but even when the picture from my adapter is totally wonking out, the on screen menus look solid. they only seem to be affected by certain other conditions. If the onscreen menu looks good, does that mean that the horizontal and video circuits themselves are good and that I should be looking toward components on the input part of the board?

[old_tv_nut]

The menu text is generated by internally syncing the character generator to the sweeps, so even if the sweep is not synced to incoming video, the characters are still stable.

The external image jumping is some kind of sync problem, either simple sync separation or improperly locking a horizontal-to-vertical countdown to the incoming signal.

So basically yes, this means the horizontal and vertical sweep circuits are OK, but something in the preceding circuits is wrong.

[Electronic M]

If back feeding the video output with input is giving different brightness and sync behavior, then on top of the sync sep being suspect, there could also be an issue with the gain levels in the video chain feeding it.

[rwagoner]

Obviously I am not a tech, though I am good at following directions for building/repairing and soldering/desoldering... Should I be looking (for things like leaky caps, I assume) on the input board (attached to and part of the main board) or just anywhere on the main board? Or -- and I know this is hard to say without actual diagnosis -- is this probably more than a bad cap?

I do appreciate the help, even if the ultimate advice ends up being to either have someone qualified to look at it or give it away if someone wants it. I certainly don't mind trying things.

[rwagoner]

I thought it might be worth showing photos. One shows the on-screen menu. Video stabilizes after being on for a while. As I write this the video is actually watchable (better than showing in photos). Can anyone recognize the show I am playing on a DVD?

[damen]

look closely at the 9-959 main board and see if there are any "blue" color caps. They would leak. You could see corrosion on the leads as they enter the board. Also, does this set have the extra PIP module ?