I have a smdm soundboard that has horrible loud scratchy sounds. I can hear the sounds behind all the scratchy mess of a sound that is coming out.
When I adjust the pots, the scratching is crazy. At minimum level all sound goes away, but it gets loud quickly. It's a mess of a sound.
This is a project restoration. When I first got it I did the basic checkups and fired it up. It played a game for a few minutes with good sound. Then the sound went all scratchy. I've completed the restoration and the game is great, except for the sound.

Here's what I've done so far:
Verified header pin continuity on the soundboard
Installed cap kit
Reseated socketed chips

I used another soundboard from another smdm and it worked great. So, that means my problem is isolated to this soundboard.
I don't know what to do next.
I would appreciate any suggestions you might have.
Thanks!

The scratchy sound is pops, clicks and garbage. It's loud. The volume does change somewhat with the pot, but doesn't change gradually. And I have cleaned the pots. Anyway, I pulled out U9, the op amp, and now the sound is fine. Just a little quiet since it isn't being amplified much.
The sound can be heard and is good, so it will work in a pinch. Would be nice if it was just a little louder, though.
So, I think my problem is a bad U9. Do you agree?

Just wanted to let everyone know that the op amp replacement UA741CP worked like a charm! Soundboard is working great now.