Quoted from Mikespinball:The CPU or AV board?
Could be either. Is there any battery corrosion at all on the CPU board? If so, likely that is where the issue lies.
First try to press on all the socketed ICs on the CPU board? If it didn't help, I would swap in the MB AV board into the SS. No need to swap the sound ROMs between the boards. Only will have wrong sounds, which will not hurt anything.
If you want to try the CPU board, you only need to plug in the J210 power connector and the 2 ribbon cables at the top of the CPU board to test out the ColorDMD.