Archive of the former Yahoo!Groups mailing list: Discussion about the Korg PolySix synthesizer

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Subject: Re: [PolySix] Re: fully recapping a vintage synth

From: klosmon <klosmon@sbcglobal.net>
Date: 2014-12-03

The first thing to look at is the Data signal at pin 2 of CN11 on the CPU board.  This is the mulitplexed signal that's sent from the front panel to the two CV demulitplexing ICs (18 and 19).  You should see a sort of "stair-step" display;  the various components should rise & fall smoothly as you turn each pot.
If you see that, then the problem is most likely on the CPU board.
If not, it's probably on the front panel, in the mulitplexing stage.  Check the pots for +5 at one end, -5 at the other;  observe the center pin as you turn the pot -- should be a smooth continuous transition from -5 to +5.

If that checks out, look at the A,B and C signals on ICs 1 and 2 on the front panel;  these, along with the signal at pin 6 of each, control the mulitplexing of the eight pot lines.

~G

On 12/3/2014 10:06 AM, jim@saltlands.com [PolySix] wrote:
 

I did not yet dive in with the scope, but could do that in the next couple days.


Just tested symptoms again.. the pots which have the unusual sound are the following: 

- All 4 VCF pots: Cutoff, Res, EQ, and KBD
- EG Sustain
- MG Level
- PW/PWM 

If someone has a general suggestion of what to be expecting to look for with the scope at the components in relation to this list, i am all ears and very thankful. I have some circuitry and component knowledge but nothing too advanced yet, and this is a great chance for me to figure some more stuff out. I very much appreciate the help.