Asteroids graphics glitch

I have an Asteroids board with a graphics glitch that ONLY really shows up
in test
mode (although if you look really carefully you can also see a similar
manifestation
of the problem on the saucers).

It affects the short horizontal 'brightness' lines in the middle of
the test screen. These are alternately offset a millemetre or two to the
right.

So, where they should look like this:

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they instead look like this:

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That's obviously a bit of an exagerration, but you get the idea.

It's definitely the board at fault as other boards in the same cab are fine.

I've seen this before on one other board but was never able to track
it down. It's not the DACs for starters as I've tried swapping them out.

It's so trivial that it's hardly worth worrying about as it is barely
noticeable when playing a game.
However, I'd like to get to the bottom of it if I can. Any ideas please anyone?

Thanks,
Phil

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Received on Fri Jul 12 15:28:47 2002