Hoping to repair one before I try building one --My TS-9 (first reissue from 1993) distorts even with the drive turned off. The two other pots respond normally. Anyone know what the source of the unwanted distortion might be? I successfully fixed 3 different issues, three different times on the same pedal before - A short circuit, a bad pot, and a bad switch. But this time I have no idea - don't really understand the circuit to know what to look for. Ideas appreciated.