[sdiy] prophet 600 weirdness

[klosmon]

Cross-posted (and hopefully not echoed...)

Hola--

I've come across a bizaare problem with a P600;  have done about a dozen of
these, and never dealt with this particular quirk...

The problem is tuning.  When first powered on, the machine goes through a
mandatory tuning routine for all 12 oscillators & 6 filters.  If it
encounters a problem (or what it PERCEIVES to be a problem), it will scale
the particular oscillator(s) out of range.  OK, that's routine.  But on
this particular unit, it always comes up with all 12 oscillators scaled out
of range.  Pressing Tune once might bring one into range;  pressing it two
to five more times will finally get all oscillators functioning correctly
-- until the next time it's powered up.
This problem is specific to the voice board:  I've switched a working CPU
board & Voice board with this unit, and the problem follows the voice
board.  I've scaled all the oscillators & filters per service manual
instructions, with no change.  I've traced all the signals to & from the
DAC (even tried the DAC in another unit, and tried another DAC in this
unit) -- no change.  I've gone through & replaced all opamps & comparators
in the tuning path -- no change.
I've removed, tested, cleaned the pins & sockets of the CEM chips &
reinserted them -- no change.
Can anyone direct me to something I'm missing here?

Thank you, and my (increasing) grey hair thanks you.

~GMM