TECH: Problem with Asteroids

[ManicArcade]

Sorry for the cross post but the other group seems pretty quiet.

I have an Asteroids that has a problem with the ships and asteroids jumping
at various rates. The faster moving asteroids, jump more rapid than the slow
moving ones but what I thought was random is quite predictable.

It's as though there is a pulse getting thru the timing circuit for the
scrolling. When in play, the player's ship if left at center position, does
not jump but when firing, it often apppears to be shooting parallel guns. A
second parallel line of fire will display. If I move the ship from the
center position, it will then jump. the jumping is first high then low.
Could this be a simple problem of a bad cap? If so, any suggestions as to
where in the circuit to look?
Clock curciut? Regulator?