Hi Paul -

> Other question: when you forcibly enable the channels, does the first
> oscillator sound in tune?

Sadly, it does not. It tends to sound perhaps slightly more in-tune than the second oscillator on a given voice, but that ain’t saying much.

> I'm wondering if it gets part way through the
> process on each channel before failing, perhaps failing on the pulse width
> or the filter. If oscillator 1 is sour, then I'd concentrate on the "Timer
> Interface Serial I/O" section. If it is in tune, then the problem may be
> elsewhere.

If I auto-tune any one voice and probe at the tuning buffer, I can see 4 quick waveforms, and that’s it.

> The auto-tune measures the period at four pitches for osc 1, then osc 2,
> then the pulse duration at two widths for osc 1, then osc 2, then the
> period of filter self-oscillation at two pitches. Sometimes you get a clue
> by where it fails.

Based on this description, on a given note it seems to be failing after the first oscillator, then jumping out of the routine.

> If you need help figuring out the Timer Interface Serial I/O section, let
> me know. Or, if you have spare parts, you could try replacing the ICs in
> that section, and hope that fixes it.

Thank you for that offer! I think I’ve got some of those IC’s around, so I think I’m just going to try the shotgun approach on the timer circuit. I’ll get those dropped in then report back.

e