Hi everyone. I just packaged up my system 11 MPU to send to coin op cauldron but before I do I figured I would give it one more try to figure out why I have no sound. Ive got all the proper power supply voltages, including -12VDC & +12VDC. The cabinet speaker ohm'ed at ~6 ohm, and the backbox left speaker about the same, the backbox right tweeter is blown and doesnt give me a reading. It should be noted that I do have speaker hum that gets louder and softer by turning the volume pot. Also the connections from speaker>soundboard and inbetween are correct.

Is there something obvious I could have missed here ? Ive got a decent desoldering station and was hoping to get this board up and running myself but my diagnostic skills arent great. If the background soundboard were working wouldnt I atleast have some sounds ? Im starting to worry that my problem lies on both the MPU & B'ground boards. My B'ground board has proto roms, and the MPU has Rev 1 roms, is there any sort of compatibility issue there ?