I am working on a Bally 6803, Party Animal specifically. I replaced the original corroded MPU with one that I acquired from a friend. This new board was nice and clean and worked great for about four or five games until EVERY coil in the game locked on and blew the playfield fuse. Replacing the fuse just blows it immediately upon power up because the game locks on every coil. I've tried the board in another game and the same thing happens.
And when I say every coil, I mean, all of the playfield coils except for the flippers. Even the flipper relay locks on right away.
I've replaced the 74154 decoder with no change. I've swapped out the PIA's and CPU chip with no change. At this point I'm thinking either ALL THREE CA3081's are blown or EVERY driver transistor is blown. Either of these scenarios seem pretty unlikely, so I'm coming here for advice before I start ripping more chips from the board.
The schematic is pretty clear that there's nothing else in the circuit (it's identical to the earlier SS Bally design), but something is forcing all of these transistors to ground as soon as power is applied. if it's not the 3081's or the transistors themselves, what could it be?
Any help you can offer would be greatly appreciated.
Here's a link to the Strange Science manual/schematic since the Party Animal schematic isn't on the IPDB:
https://www.ipdb.org/files/2396/Bally_1986_Strange_Science_English_Operating_Manual.pdf