Quoted from barakandl:
I have had to fix numerous bally MPUs where 12v or worse gets onto the 5v rail. Usually The CPU, RAM, interface adapters, and all the 7400 series chips are dead. The 4000 series parts usually live. Sometimes you get lucky and one part will go low resistance and blow the fuse / shutdown the v-reg before much else goes bad.
I'd start with checking anything in a socket you can pull out and test in another board/rom burner to get an idea of the damage.
I've been putting in sockets and removing chips/replacing with good chips, but no change. So far, z5, z36, z4, z1, u1 (6502), u5, all test fine when I throw them in a good board and power up the other game (Haunted House)
The game rom is fine, I had it in a swemmer board to test.
I mean, after all that, there's not a ton for it not to boot. There's the sn74hcto4n next to the game eprom on the piggy back board which I do not have a spare of, and I'm starting to suspect, u4 and u6 (both 6532) and chips z7, z8, z9 and z10 in the left corner of the board. Am I missing something crucial? I have +5 steady, and I used a swemmer board with the eprom without issue in it last year, so the ''system'' is fine.
I had Chris Hibler service the board a couple years back, and with maybe 5 hours of game time on it, one day just failed to boot up. I had suspected a voltage spike, but maybe not. Any ideas?