Hello.
with the -12v disconnected at 1J17, and the game is on, I get positive + 4.58 volts on the -12 v circuit at all points of it. The game plays just fine. With the volume pot turned up, it’s a very loud hum which reacts when I touch the sound input legs on U48. I have the sound card bypassed. When I activate SW2 sound diagnostic switch. I faintly here a sound file, airlock open, close, and the ahhhhhhhhhhhhhh sound. I’ve checked and checked for continuity and bad soldier joints and haven’t encountered any issues. All components are new except for a few resisters over by the 2002 transitor/amplifier.
At a loss.. game had been dead for 25 years. Before it finally died, the sound hum issue was present back then. There was acid damage in the reset section and I had to rerout some traces. Any help greatly appreciated.

Yes. And I have bypassed it as well. No change.

Hello to that replied....

The positive 4.58 volts on the -12v circuit was discovered with the -12v line disconnected at 1j17.

With the -12V connected and all things operational. Have Rottendog powersupply.

I have pins 3 and 4 jumpered together at 1j20 to keep signal from going to the sound card.

I have tested the ribbon cable for continuity, and it checks out.

I have replaced the 10uF cap. I had a hard time finding one. Any suggestions of a vendor for a new one?

99% of the IC chips on the board have been replaced. Game was dead for 25 years. Finally got game play restored. The sound had failed with the loud hum before the rest of the game packed up.

All new PIAs, all new 6808s.