I'm having a couple of issues with the sound on the High Speed I recently picked up.

#1 - The music plays and tests fine. Nice and loud. If I run the sound test, the sounds are playing but are extremely quiet. Like so quiet that I can really only hear them if I put my ear right up next to the speaker and have the music off (or better, the board that plays the music unplugged). If I push the sound test button on the board, I don't hear anything.

#2 - Hum. Lots of it. I've tightened all the screws on the boards like I've seen mentioned in other threads and it is still loud as can be. It gets much better if I unplug the speaker in the bottom of the cabinet, but it's still there with just the other speaker. I plan to replace the capacitors on the power supply to see if that helps.

I'm new to the Sys 11 thing, but from what I'm reading it sounds like the music comes from a separate board and the sound effects are right on the MPU board. I see where the amp is on the MPU board, as well as the sound roms. Since you say the caps are likely shot, I think I'll try replacing all the caps I see in this corner of the board.

@ChrisHibler - The only thing I hear is background music and the single tone when you turn it on. None of the talking, engine revs, screeching wheels, etc. I can VERY faintly hear that stuff if I shut off the music and put my ear right up to the speaker. It's so quiet I don't think my phone will pick it up, but I'll try to post a video tonight.

I forgot - I took a quick in-game video when I first got the machine running. Does this help at all?

Sorry for the potato quality.

Thanks! On another thread, someone suggested replacing the chip at U4 for a similar problem (some quiet sounds, some loud). Since it was like $0.35, I ordered one with my last parts order just in case.

Ah, I solved the quiet sounds issue. It's a little embarrassing that I missed this for so long, but the red wire in the little three wire connector that goes between the mpu board and the sound board was loose in the connector. I fixed that and suddenly there was sound.