Anyway I'm putting off explaining to y'all why this thing was broken, because it's very tempting to say "The battery leaked and ate some stuff."
(see back when persistent storage cost £oadsamoney, you'd just hook up a battery to your RAM chip if you wanted to save high scores and stuff. Williams used 3 AA's, Bally and Gottlieb used a board-mount rechargeable NiCd. Thousands of pinball computers have been destroyed by leaking batteries)
Anyway yeah I could tell you that and that'd be very neat and tidy but the details of WHAT the battery ate are WAY jucier and more interesting. My problem is I try to keep this a super accessible account so explaining what the eaten bits did and why that meant the machine ended up doing what it was doing would involve explaining how a computer works and that scares me a bit 😅