MXR M117 - faulty regen knob? [SOLVED]

[plush]

Hi guys

I got asked to check that old smelly mxr m117. Apparently it's regen (feedback/resonance) knob is not working properly and does not provide as much change as you can see on this video:

1st I've wiped all rosin with a solvent
then, I've checked the pcb for any cold solder joints with my dmm
checked all resistors and pots (all intact)
still not sure about caps, at least no shorts
BBD clock is okay (I've checked it with my scope, just in case)

I've drawn all my voltages on the schematic below, they seem ok for me
Unfortunately, all trimmers are jammed with a healthy portion of solder (thanks, MXR!) - maybe 20k feedback trimpot is the reason?

I feel mentally exhausted, since i can't come with any idea or use my soldering iron to unjam the trimpot (i got asked not to do it by the guy who brought me this pedal)...

[plush]

I got told to check sad1024 input and output levels. Maybe faulty ic is the reason.

[Fender3D]

There's no "feedback" trimmer...
the 20K @ SAD's outputs will balance the wet signal with dry.
If you have a good balance (wet should be 5.5dB lower than dry when measured @ mixing resistors 150K and 82K or IC1b's out and IC2b's out) you don't need to touch it.

Check signal @ 15nF and 120K junction and report,

[plush]

Check signal @ 15nF and 120K junction and report,

Sorry, check signal for what?

[Fender3D]

There you'll find the signal you feed back for feedback...

[plush]

There you'll find the signal you feed back for feedback...

Okay. 500mvpp 1Khz input signal loses nearly a half of its amplitude when measured on that junction.

[Fender3D]

With the regen knob fully CW signal should have the same amplitude as signal @ IC2b's out.
Capacitors just trim out the low end.
If you used 1KHz to check, they should not dim signal that much...

BTW
check for wet signal level:
BBD's pin2 (input), pins 5 and 6 (first half output), pin 15 (2nd half input) and pins 11 and 12 (2nd half output):
signal should not decrease, actually it might increase.

[plush]

With the regen knob fully CW signal should have the same amplitude as signal @ IC2b's out.
Capacitors just trim out the low end.
If you used 1KHz to check, they should not dim signal that much...

Ok, i'll rechek it

BTW
check for wet signal level:
BBD's pin2 (input), pins 5 and 6 (first half output), pin 15 (2nd half input) and pins 11 and 12 (2nd half output):
signal should not decrease, actually it might increase.

Pin 2 shows input sine without any distortion, rotating regen knob adds some sort of modulation to it

pins 5 and 6 are okay

pin 15 - i'll check once i'm home from work

Pin 11 and 12 output looks strange to me
Sorry for the crappy photo, had no time to connect scope to pc
grid - 1volt/div

[Fender3D]

~700mVpp... looks fine...
Now check if this signal gets out of IC3b (pin 7)

[Fender3D]

1x probes?

[plush]

1x probes?

Yep, x1
Dat pic showed ~7V ptp, which is crazy. Also that waveform is not what you want to see in working bbd.

Second half of sad1024 is oficially dead. It is the reason.

Changing sad1024 (yeah i managed to find working one) solved the problem.

Anyway, thanks for your help.