I originally picked up some broken pedals so I could use the cases for my own prototype designs. However, this Tokai Analog Delay would be really cool if I could get it working again. It’s an ’80s (I’m guessing) knock-off of a Boss DM-3. It uses an MN3205 BBD chip and an NE571 compander.
Plugged into my rig, I immediately saw the problem – It wouldn’t turn off! The switch on this pedal did nothing, the LED stayed on no matter what I did. I decided to investigate, obviously.
The two 2SC2021 transistors on the bottom left are the switching BJTs for the FET switching circuit. It looks like somebody tried to fix it with a 1000000 Watt soldering iron, since the PCB was charred black on the underside. With some solderwick, I removed the attempt and rewired it according to this schematic. Boom, good as new.
What’s really interesting is the amount of oscillating this pedal does. At the high range of the feedback control, you get some really crazy squeals.