Spy hunter repair

I have an upright spy hunter that I am trying to fix.
 
The road plane of the graphics is slowly scrolling to the left (it wraps
around).
 
The sprites (car / enemies / weapons truck, etc) along with text / graphics
are all staying steady as expected.
 
I swapped out the video board and that didn't do anything different.
 
Suggestions on where to look for the road part of the board?
 
Thanks,
David

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Received on Sun Apr 26 15:36:50 2009