Midas PR 04 strange oscillation problem

[mkiijam]

This is the relevant section of an AUX return module that is oscillating in a strange way.
1. Turning the SEND LEVEL control causes it to go into oscillation about 3/4 of the way up.
2. #1 is true with no INPUT signal.
3. The TREBLE and BASS controls change the pitch of the oscillation from "motorboating" to past hearing range (testing with headphones)
4. Shorting PIN 2 of IC 5 stops the oscillation.
5. Disconnecting the input trace stops the oscillation, however there is "nothing" on the AUX BUS.
6. Subbing in another channel and it works fine.
7. Placing the bad channel in the other AUX slot still has the issue. This is relevant because if there were noise on that AUX BUS it would follow the "slot"
8. This schematic is NOT the right one but is fairly close. C31 and C32 are not in the channel I am working with.

I'm just stumped at why removing the input to PIN 2 of IC5 stops the issue?

This is the relevant

 

[Dreams]

This thread reminded me that i needed to fix a PR05 channel strip that had developed an oscillation suddenly, similar symptoms to what you describe. Looked at it today, the problem turned out to be a pin on the treble pot had broken off. Similar circuit to your as well.. Those blue rubber/whatever sleeves can hide bad solder joints. I'd visually check the integrity of those pots and their wires first, but might need to go through the whole module, but look for something around those pots or that network there

 

[Dreams]

Those TDA1034 chips are (iirc) an early 5534. Shorting pin two to ground will put bout input pins at ground and kill the output entirely. I don't know why this would kill your oscillation (which i believe to originate in the next stage here) but in my case, removing the feeding amp also killed my oscillation so

 

[mkiijam]

Mine turned out to be an actual OUTPUT to INPUT scenario. A previous tech misplaced a jumper and was actually doing just that!

 

[Dreams]

Lol wow well yeah that'll do it! Glad you got it sorted out