In the process of fixing a display issue, I have broken my sound. I get no game sounds whatsoever. Not even a boot-up beep. I still hear a slight hum out of the speakers, so I don't think I blew them. I've checked all my connections, and everything seems good in that regard. In doing that, I did notice that on CN21 on the MPU board, the left upper-most pin was missing. This may be normal, as the schematic for that pin shows an "E"." Other than that, connections look fine.

Display and gameplay are fine. Anybody got any tips that could help me diagnose the problem before I go down the path of securing a new board?

Thanks!!

Yep - ribbon cable is good. Had continuity all the way through.

Just a follow-up on this topic. I finally gave up on my own ability to diagnose and fix, after nothing worked. Sent the sound board out to Clive at Coin-op Cauldron. It came back in no time flat, and is working like a charm. Clive's work:

Removed all three ROMs and verified internal data (Vc +/- 0.25v). ROMs checked for latest revision of software. BSMT2000 and Microprocessor removed and tested. New 6116 Static RAM IC and 28-pin IC socket. 2x 22uf/50v/`105 capacitors (C17, C59). 2x 470uf/25v/105c capacitors (C31, C52). 1000uf/25v/105c (C30). Upgraded CN2 power input header to high temperature version. Reflow solder for all header pins. Board cleaned up.

$78 for the sound board work, plus $12 return shipping. Very satisfied with his work. His website pretty much tells you what he'll charge.