Fender Rumble 500 Power Supply Issue

[g1]

First I would try disconnecting the jfet Q3. Either of the legs connected to R42.

[nevetslab]

I don’t recall their pot details. On larger dia pots that have the mechanical terminals riveted to the resistance wafer, I have had to generally tap the rivet between a suitable center punch pin mounted in a vice and further flatten the other side of the terminal revit to restore solid mounting and restoring conductivity.

[Bryan]

I will try disconnecting Q3. Is it just a switch shorting out R42?

I know what you are saying about the rivets. These pots were split cleanly right at the wafer. They must have been hit somehow.

[g1]

Q3 shorts R42 but brings the signal line much closer to ground, so may be acting as a mute.

[x-pro]

... I get nothing at Pin 8 on U3

????
This is the power supply pin U3.

Is there a reason I only get signal on one side of C18? I get signal between R37 and C18 but not C18 and R43.

What signal is being input? If the frequency is below 480 Hz, it will be attenuated. The normal signal level should be just over 100mV.

[g1]

????
This is the power supply pin U3.

U3 is TL074 (quad), pin 8 is an output.

[Bryan]

I'm using 100 hz. That's what it says in the schematic.
Anyway, I'm good on the Overdrive circuit now too. All is working. My bad resoldering on U4 pin 11.
I still get the balance shift on the rails when I plug in the fan. I get -12v instead of -10v. Maybe it is a bad zener D26. But it is now making much better sounds than when it arrived.