mjrippe wrote:Thanks for the detailed reply! First of all, C5 plays correctly with no noises, not silent, all other C notes have the crackle/pop.
OK, ignore pretty much everything I said!
Capacitor C68 is ceramic and will be the next thing I replace.
Again, the new TOG has clean output. I have replaced the 4013 (IC5), but pin 13 still shows the noisy waveform - it looks like jitter on the square wave, not voltage spikes. When the noise happens it is as though the low parts of the square go high but with ripple, if you know what I mean. Perhaps a video clip would help?
Have you checked the PCB tracks around that second half of the 4013, and between it's output and the 10430? Pics of that noise would be good.
The whole C5 vs C1-4 is a bit confusing. Again, pin 14 on IC3 is a clean square wave. It is pin 40 on IC1 as well as pin 13 on IC5 that show the problem. The other half of the 4013 (IC5) is working fine, octave switching is flawless. Since the C5 note is clean, is it possible the problem is coming from the S10430?
Pin 13 on IC3 is an envelope input. If you hear the note C5 play with no problems, I would forget about that and concentrate on the lower C1-C4.