This was an old repair that I did a while back, there was a lot wrong with it, surprisingly all CPU board issues...
Symptoms: -5V rail was shorting to ground
Solution: The bypass cap connected to the -5V rail had shorted, needed to be replaced. One thing to note is that several capacitors on this bubble bobble boardset had started leaking, so I ended up replacing all the capacitors with new ones.
Symptoms: Not booting
Solution: The game was stuck in a reset loop, it ended up being a bad 6264 RAM chip (the work ram). Game fired up after replacing it.
Symptoms: Garbled up graphics and Common RAM error
Solution: The garbled up was an easy one, there were two corrupted EPROMs, reprogrammed accordingly. The common RAM error had me stuck for a while. To make the story short, it ended up being the PAL at IC49 ended up being the cause. Replacing that solved the issue and brought the game to full working order.