Game: Flash Gordon (this may not matter)
Symptom: With this particular SDB is installed one wrong sound is played when certain switches are triggered. Also the background sound will not restart at times.
Analysis: The game behaves fine when tested with four other SDBs I have on hand. It only misbehaves with this particular SDB.
My first thoughts were this is a data issue so I approached it that way. I initially suspected the 74L156 but it is fine. Finally after a lot of head banging and misdiagnosis I booted the game with ONLY J3 attached. J4 is not connected, so no data that is being passed from the MPU to the SDB to the sound board should be affected, but it still misbehaves as described above (wrong sound, no background sound at times). But if I hook up one of the four other SDB with only J3 attached the game acts fine.
Any help is greatly appreciated!