Discussion about the Korg PolySix synthesizer

IC17 pins 3 and 4 look like part of the tape out circuit.
Are those really the ones you are looking at?

Also, one thing I forgot to mention.   The voltage at the output of
the 4051 should track the panel potentiometer, I think, although there may be a scaling
there, for instance the pot may be set up to swing from 0 to 10 or 0-15 volts, 
and the corresponding output of the 4051 may only swing from 0-5V for instance.
If you are seeing
a big step when you hit a particular spot in the pot's rotation, then that may 
mean that one bit of the DAC is not working.   For instance, say the DAC value is 
changing from 0011_1111 to 0100_0000 and the D6 bit doesn't work.   Instead of
seeing a small step up, you would see the value jump back to 0 when you hit that
point.   Not sure exactly what you are seeing, but I would replace the two 4051's 
first, then try to determine if the whole range of the DAC is working by slowly 
turning one of the pots and watching the corresponding output of the 4051 on the scope.

BTW, the charging resistor R86 is 2.2M, so if you are using the x1 position of your scope
probe (1M ohm) then probing that point would lower the voltage.  Is the "ST" signal on 
the left end of C35 switching?  In general, you would want to use the X10 scope probe 
position if you can, since that has a 10M input resistance and will load the circuit a lot
less.


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On Tue, 8/30/16, 7zlwncpbis4x22jwvkd4oc5hzu2njcsjeup42is6@yahoo.com [PolySix] <PolySix@yahoogroups.com> wrote:

 Subject: [PolySix] Re: Trying to Restore a P6.
 To: PolySix@yahoogroups.com
 Date: Tuesday, August 30, 2016, 7:34 PM
       
              Thanks again for your patience and guidance on
 this, Bob. I'm going to get this working right
 eventually.    I see no voltage change on pin 1
 of IC 14, and pin 3 exhibits odd behavior, in which putting
 a probe on it seems to make the voltage rise or fall to
 settle around 12.8V. The voltage at pin 2 rarely rises above
 3V, due to the fall-off in voltage I see on some of the
 controls, so perhaps I'm seeing the V at pin one due to
 the fact that the - input is always less than the +
 input.    Also, I'm seeing a constant 4.97V
 on pins 3 and 4 of IC17, which seems odd for it's
 outputs considering it's function, and what is going
 into it. I bought some extra 4011s tho, so not a problem to
 swap out, but please clue me in if I am misunderstanding the
 circuit.   And, I will wait to see how IC10
 reacts after installing a new IC18, Those connections check
 out continuity-wise, and I get what you are saying about
 feedback circuits.    First I want to pull the
 board and make sure I didn't do something stupid on the
 bottom while correcting bad traces, that might have caused
 the 5V line to get crossed.