Discussion about the Korg PolySix synthesizer

Hi, Johannes --
Replies inline.
On 2/15/2013 10:49 PM, Johannes Hausensteiner wrote:
>
> Hi,
>
> What happens if you ground the signal CN06-2?
>
Shorting the signal at CNo6-2 defeats the mod signal.
>
> I am not sure what you mean by "it is visible at R9". Does this mean
> that you can see the LFO wave at R9 (outside end) with the mod wheel
> turned down completely?
>
Yes -- with the mod wheel down, LFO is showing up at the VCO mod opamp 
(but no where else).
>
> What happens when you short the mod wheel wiper to GND?
>
Nothing, unfortunately.
>
> What happens when you remove KLM-369 / R16?
>
No help. As stated previously, I swapped in a working CPU board and 
there was no problem;  this would indicate to me that the front panel is 
OK, and the problem is on the CPU board.
>
> Try cleaning the PCB.
>
Yah, cleaned it with 99% alcohol.
>
> Check again that the cuts you made to the PCB traces completely
> separate.
>
Did that;  also disconnected the 1 and 2 wires from CN06 entirely and 
hardwired them to LFO out at R25 and VCO mod in at R9 -- no help.

Will keep slogging on - might just have to disconnect the mod wheel on 
this one.
Thanks.

~G

>
> Good luck!
>
> Johannes
>
> On 2013-02-16 07:30, klosmon wrote:
> > I'm currently repairing a battery-damaged CPU board, and I've just about
> > got everything working again -- except for the LFO bleedthrough into the
> > VCO modulation circuit.
> >
> > I've repaired over three dozen of these things the past few years, and
> > come across this problem repeatedly.
> > I was able to solve it several times in the past by cutting the circuit
> > board trace at CNO6-2 and at the outside end of R9, and joining them
> > with a jumper (taking care to move C43 back into the circuit). This
> > bypassed the parts of the circuit board that caused the LFO signal to
> > bleed into the modulation circuit even when the mod wheel was fully 
> down.
> >
> > In the case of this board, however, that procedure isn't helping --
> > there's still LFO modulation audible on the VCO (and visible on the
> > scope at R9). I though it might be something from the other LFO mod
> > path from the front panel mod switch (through ICs 1 and 2, finally
> > through R11), but grounding that signal doesn't stop the mod effect.
> > And, it's only appearing at the VCO mod circuit; no sign of it at the
> > VCF or VCA.
> >
> > Thinking it might be something on the front panel, I swapped in a
> > working CPU board, and the problem went away; obviously the fault is in
> > the first CPU board.
> >
> > My eyes are starting to blur going over these schematics; has anyone
> > here dealt with this problem successfully?
> > If so, I'd love to hear about it.
> >
> > Thanks.
> > ~GMM
> >
> >
> > ------------------------------------
> >
> > Yahoo! Groups Links
> >
> >
> >
> >
>
> 



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