I wrestled with the sound on pinbot recently. Here are some things to consider:
The main sounds (switch hits, and such) and all the speech, are generated by the sound CPU on the main board. The background music is what comes from the sound board. For me, all I was getting was background music.
I believe there is a trimmer pot on the sound board that mixes the two signals together. Give a few wiggles to see if it helps. They can get dirty and finicky.
SOUND TEST will run through main CPU sounds and speech. MUSIC TEST Runs through sound board sounds (music, of course).
People tend to have success when changing the CVSD chip, but I like to KNOW that's the problem before I change it.
No, this doesn't give you an answer, but might spark something for you.
Good luck,
Jeff