Bad caps, damaged traces are the two culprits I can think of. I'm used to seeing this behavior on SegaCD consoles rather routinely and I've fixed it a few times. X'EYEs are very easily damaged as I've found out and can usually be fixed by someone who has expertise in them.

Most people don't. I do. They are NOT the same beast the SegaCD is and people make the mistake that they are.