Note to self: The Alltek SDB and the Bally SDB are not exactly the same electrically.
When I picked up a non-working project Mata Hari months ago, I re-pinned all the connectors and got it up and running with Alltek boards. Been working for months. Got the original Bally boards back from being repaired and put them all in - boots fine but no solenoids. Go back to the Alltek SDB, works fine. Put the newly repaired Bally SDB in, boots all the way and can even start a game but no solenoids.
Probed the Bally SDB with a DMM - all TP's fine with voltage except TP3 (showed 0V, should be 5V). I tied the 5V from TP1 to TP3 with alligator clips, and the Bally SDB then worked fine.
I then took a closer look at the J3 connector (specifically the jumper wire connecting pins 13 and 25). No continuity. I pulled the jumper wire out, and sure enough one of the pins that I had re-pinned months earlier was mangled. I re-pinned the jumper wire, put it back in, removed the TP1 to TP3 alligator clips, and everything works again with the Bally SDB.
The Alltek board apparently does not need that jumper wire present in the J3 connector. I screwed up the crimp months ago and never knew it because the Alltek board just worked. When the Bally SDB didn't work, I never suspected there to be a wire issue given that the Alltek worked fine!
SDB J3 Jumper Wire - Damaged Pin.jpg