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.