VCO debugging

I can trace a signal to the 2164 that changes with pitch (pin 10) but nothing after that… Any suggestions where to start?

You mean pin 11?

Remove IC7 (TL072), and feed the signal that leave pin 12 of IC6 (IC7) to a 1k resistor. Post here the voltage you read for C1, C2, C3, C4. Would be nice if you posted the voltage on IC6 pin 11.

What are the voltages on IC7 pin 7, and IC8 pin 7?

Check Q1, C9 (polarity of the transistor and capacitor across wrong pair of holes).

And check voltage at IC8 pin3 (comparator threshold).

heh. C9 was inserted wrong. Always the little things that take me down and that was the first thing I checked too. Here I am busting out the scope and desoldering equipment. Thanks for the nudge in the right direction :slight_smile: