Tech: Asteroids screen image shrinkage?

Dudes,

My Asteroids CPU displays an anomoly. The X width output
will momentarily squash the image all the way to the left,
and then re-focus the screen to the full screen play. It's
odd, the image will compress X-wise to about 30% of the full
screen image on the left hand border. I have localized it
to the CPU, because the monitor is fine with other boards.
(all right, I know it seems obvious that is was the CPU, not
the monitor...).

Any thoughts what causes the X-output to freak like this?
Capacitor attenuation on the CPU somewhere. (I have to dig
out my schematics again!)

Ace

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