70's home-built mixer - please help me id missing chips!

[ultrajosh]

I did some experimenting and found that if I leave the socket that's 2nd from the bottom empty, it works fine - pan works, solo button works, etc.

If I put chips into that socket I get all kinds of squealing and feedback when I adjust the pan pot. It seems to be associated with the echo send, echo pan controls, so no biggie, I just left them out and reassembled the board and now I'm in business with a stereo output.

Any idea why including those chips would cause the feedback problem? The power supplies look to be all in the same places... Maybe it's the echo part of the Master section?

Also, I have to keep the main stereo output set VERY low (like -45 db) or it hisses a lot. If I keep it down low and crank the individual channels I get a clean sound. But it seems weird that I would have to keep the mains so low to avoid hiss.