I turned on my 4 player X-Men cab for the first time in a few months, and of course a new issue presented itself! All the sprites have 4 or 5 vertical lines surrounding them, and follow them around as the sprites move. Everything else works fine.
Replace it with a 27C800 eprom that's programmed with the data from mame. Cut the old maskrom out and desolder each pin one at a time so there's no risk of pcb damage, at least that's how I do it.