Here’s another Boss DD-3. The pedal gives signal in bypass, with effect engaged there’s just dry sound.
Someone has done some repair to the circuitboards power section seen in the upper left on this image.
The Mode selector rotary switch out of the chassie for replacement.
Old vs new rotary switch.
So what’s wrong with it. Found that C34 was broken, it did not pass any signal to the expander circuit. Had it replaced and got the delayed signal through the circuit, though at to high level and distorted. C31 was the cause of that problem. With C31 replaced the pedal works as it should. The tantalum capacitors C32 and C33 was also swapped with new ones as they do tend to fail in time. Checked and adjusted the high and low end of the Master clock frequency.
Here’s the service notes: Boss DD2-DD3.