Discussion about the Korg PolySix synthesizer

Oops, I was looking at IC7 on the KLM-367, not the 366 board. Where the heck is IC13 on the 366?

From: backshall1@bellsouth.net 
Sent: Sunday, June 24, 2018 8:49 PM
To: PolySix@yahoogroups.com 
Subject: Re: [PolySix] Filter cutoff not working. Thermistor?

  Also, from the way it is acting, it sounds like you have a 393 in the IC slot where it should be a 4558, but IC13 is for PWM speed and MG speed, not Cutoff. Cutoff should be on IC7 pin 7.

From: backshall1@bellsouth.net 
Sent: Sunday, June 24, 2018 8:43 PM
To: PolySix@yahoogroups.com 
Subject: Re: [PolySix] Filter cutoff not working. Thermistor?

I hope you mean +-5V, not 14. I’m pretty sure there are no pots connected to the 15V supply.
Don B.

From: anthony.putzier@gmail.com [PolySix] 
Sent: Sunday, June 24, 2018 7:46 PM
To: PolySix@yahoogroups.com 
Subject: [PolySix] Filter cutoff not working. Thermistor?

  
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!