I was having problems with the sound card blowing the F3 fuse (12 volts to regulator). (see this post: https://pinside.com/pinball/forum/topic/short-in-12-volt-but-where
So I replaced the sound card from another known working Trident - the fuse didn't blow but I have no sound. I checked the 5 volts and 12 volts test points on the card and they are good. I checked continuity from the J3 connector to the speaker and the volume pot and that seems good. Then I replaced the speaker and pot from the known working machine and still no sound.
What to look for next?