Bubble Font Russian Big Muff Help

[slurprider]

Hello. First time posting. I recently acquired a Bubble Font Green Russian Big Muff that isn't functioning. It has some sort of wacky power supply mod where someone attached the battery clip wires to an added dc power jack. I'm not sure if this is the source of the problem, but I thought it was worth mentioning.

Anyway. The pedal passes signal when bypassed, but when I switch it on, all it does is make a high pitched squealing noise. I don't really know where to begin with troubleshooting this, as I'm new to pedal tinkering and such. Any help is greatly appreciated.

Also, sorry if this isn't the place to ask this, but I am desperate to get this pedal working.

[doof]

hi there,
have you measured the voltages of each leg of the transistors? That high pitched squealing sound like something similar to the feedback/oscillation mods i've seen for this pedal.  maybe a bad transistor?  very amateur guess on my part.  if you post them, i'll try to get around to measuring the voltages on my bubble font in the next day or two and we can compare.