[sdiy] Prophet 10 / OB-X

[Tony Clark]

> Prophet 10
> 1: Can anybody tell what the voltage must be at the Power Supply. I measure
> different value's as what is written at the pcb board.
> 2: There are two voices board in a P10. I have the schematics of the P5. Can
> somebody help me at the part of the schematics of the P10  which controll
> these voice boards.

   Not sure about the first one, probably normal +/-15V and +5V.
   For the second part, you will need the P-10 supplimental service 
docs.  It's very small compared to the P-5 service manual, but will 
probably have what you need in it.

> OB-X (8 voices, curtis based voice boards)
> After tuning tuning two voices became disabled. If i calibrate these two
> voice wrong,(instead of that two leds are on only one is on) one of the not
> working voices is working after (auto) tuning. If I disconnect one board,
> the not working voice also works after autotune.  I have found the
> schematics at internet but i can't read the text at these. Has somebody
> better scanned schematics for me. The part i am looking for is the voice
> board and the part which is used for the tuning section.

   There are two issues with the OB-X.  First are the crappy pots.  Take 
a look at my well documented page on this:

   http://aupe.phys.andrews.edu/~clark/emusic/oberheim/obxupgrd.html

   I'd suggest doing the above upgrade and see if it fixes the problem 
first.  If not, then try the below:

   The second part is that for some unknown reason, the op-amps in the 
signal path of the auto-tune go flaky.  Don't ask me why!  As far as I 
know, there's no good reason why op-amps should start leaking current 
unless they were zapped by static, but never-the-less, it does happen.
   To the _right_ of the CPU card there will be 8 TL-082 socketed 
op-amps.  These are the auto-tune lines.  Replace them.  Most likely the 
problem will disappear!

   Hope that helps.

   Tony

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