Fixing an ever-so-slight wiggle in video

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ashembers

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May 8, 2020, 11:57:23 AM5/8/20
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Hello,

I am trying to fix up my Vectrex for sale, and it is actually in very good condition. Since I got it 10 years ago, it always had a slight wiggle that was only noticeable to me while playing Mine Storm, and something would blow up on the left side of the screen (explosion lines would have a momentary wiggle). Or in Berzerk, when you exit a room and everything scrolls to the left. I.E., something about the left side on this Vectrex is key.

What is looks like in Berzerk > https://drive.google.com/open?id=1Bbtg1cDAKKyphj9q19qPJxgnK9ivOOFG

Things I tried already:

- Recapping about 10 years ago
- Trying to change the video on the 5 potentiometers to recenter, widen, squish, slant, etc
- Replacing IC303's chip with an NTE859

Aware of the tube voltage, I have not touched the yoke or anything to do with the picture tube.

So if you were trying to fix this up, what else might you look at?

Thanks for your thoughts,
A


ashembers

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May 8, 2020, 12:00:54 PM5/8/20
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I should have also mentioned that the Diag cart output looks very good - lines do make good shapes and there's no distortion in static lines. Maybe it's better to say that on the left side, moving lines show the wiggle.

Computer Nerd Kev

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May 11, 2020, 4:40:05 AM5/11/20
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I'm not having any luck getting the picture to load from Google
Drive. Bound to be just a problem with Firefox but I'm not going
to put too much time into it. I'll just guess.

One thing to consider is whether the "wobble" is just horizontal or
vertical, or both. If both, then besides IC303 which you've already
tried replacing, IC304 and IC301 could also be suspect. IC302 could
be suspect if the wobble is only the Y-axis (vertical).

IC305 has to be suspected too in any case, as well as the transistors
Q301/Q302 that control it and their associated components. Though it
seems less likely that a problem there would only occour in
combination in such particular circumstances as you describe.

Check the logic board for poor solder joints, particularly on
capacitors (including the smaller signal ones that you probably
didn't replace).

It sounds like it might be one of the amplifiers trying to oscillate,
so I'm thinking it's either the amp itself (including those inside
the DAC and analogue switch ICs mentioned), or a component that was
intended to subdue such oscillating tendencies that's no longer
working properly (eg. a dry joint on one of the capacitors, including
the low-value non-electrolytic ones).

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