Clearly something in the autotune circuitry is not working. There is a comparator
that gets fed one voice at a time. The comparator output is used to gate a higher
frequency clock into a counter, for one or sometimes more cycles of the comparator
waveform. By counting high frequency pulses that fit into a period, or several, of the
oscillator output, they can measure its frequency, and figure out what the control
voltage needs to be to get it exactly in tune. Usually 4-6 different notes up and down
the keyboard are measured, and CV's for notes in-between them are interpolated when
you are playing.

I would use a 'scope to see what the waveforms look like during tuning in this circuit.
Was helping a friend with his OBsx that had a tuning problem. We ended up replacing
a bad data bus buffer that was used to read the counter after tuning had completed.

Good luck,

Bob


--------------------------------------------

On Tue, 7/21/15, richtrix@... [oberheim] < oberheim@yahoogroups.com > wrote:

Subject: [oberheim] Autotune on OBXa suddenly shutting down all voices
To: oberheim@yahoogroups.com
Date: Tuesday, July 21, 2015, 12:28 AM


I have an OBXa that I finally got to 100% percent
with a lot of help from here and some dumb luck a few months
ago. I have the Encore MIDI kit. I haven't touched it
for about 2 months or so since I've spent any free music
typed time fiddling with some Linn 9000s I'm trying to
get working. The Obie worked just swimmingly the last time I
used it. Now though... everything works find and sounds good
but when I hit autotune instead of zipping through the
voices like it does usually it spend about 2 seconds on each
voice and then disables all of them. Any ideas what could
have happened in these two months of inactivity Doesn't
matter how long the board is on before hitting autotune...
get same result.  
Sincerely,Rich
Clarke