[sdiy] prophet 600 weirdness

[Tim Parkhurst]

A bad analog switch or multiplexer? Or possibly a bad reference voltage
somewhere (a flakey zener regulator?). 

Just a couple of guesses.



Tim (that's MISTER Wild Guess, thank you) Servo

"Imagination is more important than knowledge." - Albert Einstein




> -----Original Message-----
> From: klosmon [mailto:klosmon at earthlink.net]
> Sent: Wednesday, September 15, 2004 11:21 AM
> To: analogue at hyperreal.org; synth-diy at dropmix.xs4all.nl
> Subject: [sdiy] prophet 600 weirdness
> 
> 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
> 
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