In for repair was an Irem M72 arcade PCB with Apocalypse’s M72 Multi game solution installed. Sprites were randomly corrupting during gameplay.
The fix ended up being simple and straightforward – the plastic spacers seperating the bottom board from the middle board didn’t provide enough clearance. The middle board would sometimes “sag” on the struts and the bottom of the middle PCB would scrape against the top of the Multi PCB where it attached to the top of the bottom PCB. This was obvious after seeing how the labels on the Multi PCB EPROMs were getting scratched up by the solder legs on the bottom of the middle PCB.
Installing longer, sturdier support mounts gave the necessary clearance and cleared the problem right up.