Discussion about the Korg PolySix synthesizer

The thermistor is between IC13 pin 1 and the other half of IC13.
If pin 1 is misbehaving, I don't think the thermistor is the culprit.
pin 2 is a virtual ground on IC13, so it should be at 0V if the op amp
is working amd has feedback.  If IC13 pin 1 jumps from the negative 
rail to the positive one, that sounds like the op amp does not have feedback, 
which in this case would be R64.   If that's open, then the op amp behaves 
like a comparator with one input at ground.   Check the resistance from pin 1 to pin 2
on IC13 with the power off.

   Bob


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On Sun, 6/24/18, anthony.putzier@gmail.com [PolySix] <PolySix@yahoogroups.com> wrote:

 Subject: [PolySix] Filter cutoff not working. Thermistor?
 To: PolySix@yahoogroups.com
 Date: Sunday, June 24, 2018, 7:46 PM
 
 
  
 
 
 
   
 
 
     
       
       
       I am in the middle of restoring a p6 I aquired
 recently and have been unable to troubleshoot the cutoff not
 working. Nothing effects the cutoff (EG, KBD trk, etc) I
 have traced the +-14v signal from the pot on the face of the
 synth to pin 2, ic13 on klm366. Up to that point everything
 works as I would expect (the voltage varies from -14v to +14
 as I turn the knob from low to high). After the first opamp
 stage of ic13 (pin 1) the voltage jumps dramatically when I
 turn the knob from -13 volts on the lower half of the turn,
 then jumps to +14 on the upper half of the knob turn and
 next to nothing in between. I have replaced ic13 and that
 didn't fix it. Could it be the thermistor th4 after
 ic13? Any help would be appreciated! Thanks!
 
     
      
 
     
     
 
 
 
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