Not sure if this will help, but on the adapter I built, the JAMMA service switch added a credit for all boards. I'll have to see if I still have my adapter to verify what pin I connected it to on the boardset. Mark's reply on the the thread I started (linked below) talked about missing pull-up resistors while his reply above mentioned connecting +12V to some pins. Maybe they have the same effect?
And the document linked above (
Taito Switcher at mirror of Ionpool) adds a jumper wire. Maybe this is getting the +12V to the right place? But I wonder if this jump causes any issues if the board is plugged back into an original cabinet?
I built this adapter (plug Taito boards like Jungle Hunt into a JAMMA harness) many years ago and it has worked well for dozens of boards. Now I have a couple of boards that will not credit up! I can get them to credit up with the service switch or injecting a high signal on A COIN or B COIN...
forums.arcade-museum.com