Exidy Crackshot sprite issue

Brick Top

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OK guys, I have a Crackshot that I have been slowly resurrecting. Fixed some issues here and there, and now have a booting, running, shooting, and playing game. Almost.

This issue deals with any sprite that moves across the screen horizontally. They skip.

Makes it really hard to shoot targets that are constantly disappearing, then reappearing further across the board. Its very regular, there for a second, gone for a second, again and again. Sprites can move vertically just fine.

All initial tests pass. RAM, ROM, CRC checksum etc..If I go into the extended menu, the only test that fails is the collision test in the X coordinate. I think its under the heading of interrupt test.

I am thinking that its a RAM issue, even though the RAM tests say good. Like the RAM that tells where to draw the sprite is getting stuck, and then unstuck as new data is written to it. Make any sense? Or something that controls the address lines to the RAM?

I have searched quite a bit and the closest thing I have found is a guy who claimed to have a 440 boardset that had "flickery sprites" if the switcher voltage was not just perfect.

This game is running off a switcher. It did actually work just fine for a few days as well.

Looking for any thoughts here. 440 boardsets are such a pain, cant probe the main PCB, because the audio one covers it up, cant run without the audio, because that's where the power comes from. Schematics in the factory manual are pretty much unreadable. Grrr!
 
Update:

I have now made a test rig so I can probe the main and sound boards while out of the game. I have also made it so the two boards don't have to be attached to run either. The ribbon cable is still connected, but the through PCB pins are not.

The problem lies on the main PCB. Got that far.
 
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