Discussion about the Korg PolySix synthesizer

On 2/16/2013 10:37 AM, backshall1 wrote:
>
> Man, there's a good candidate for a clone board.
>

Yah, but the customer doesn't want it.
>
> Are you sure you want to
> continue with this thing? Has the old trace been cut away at both ends, so
> it doesn't come near R9 anymore?
>
Yes.

> Has IC8 been removed, the area cleaned, and
> replaced with a new socket and chip?
>
Haven't tried that yet -- I'm putting the whole thing aside until 
Monday, at which point I'll start over & see what I missed.
>
> You really are running out of
> possibilities here.
>
Yeah, bailing is starting to look attractive.
Thanks.

~G


>
> Don B.
>
> _____
>
> From: PolySix@yahoogroups.com <mailto:PolySix%40yahoogroups.com> 
> [mailto:PolySix@yahoogroups.com <mailto:PolySix%40yahoogroups.com>] On 
> Behalf Of
> klosmon
> Sent: Saturday, February 16, 2013 12:38 PM
> To: PolySix@yahoogroups.com <mailto:PolySix%40yahoogroups.com>
> Subject: Re: [PolySix] LFO problems again
>
> On 2/16/2013 5:31 AM, backshall1 wrote:
> >
> > I've had a couple where I had to remove the connector header from the
> > board,
> > clean the bottom of the header and the board, then solder it back 
> on. That
> > was a real pain but it fixed the problem when doing the jumper didn't
> > help.
> > Apparently there was some leakage from pin 1 to pin 2 of CN06
> > underneath the
> > header.
> >
> > Don Backshall
> >
> On this unit, CN06 (and the area underneath) was so badly corroded that
> I removed it entirely and hardwired the data and address lines. The
> wires for Mod and LFO are wired directly to the board at R9 and R25;
> the traces from the CN06 area have been cut completely to remove any
> possible influence.
>
> ~G
> >
> >
> > _____
> >
> > From: PolySix@yahoogroups.com <mailto:PolySix%40yahoogroups.com>
> > [mailto:PolySix@yahoogroups.com <mailto:PolySix%40yahoogroups.com> ] On
> > Behalf Of
> > klosmon
> > Sent: Saturday, February 16, 2013 1:31 AM
> > To: PolySix@yahoogroups.com <mailto:PolySix%40yahoogroups.com>
> > Subject: [PolySix] LFO problems again
> >
> > 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
> >
> > [Non-text portions of this message have been removed]
> >
> >
>
> [Non-text portions of this message have been removed]
>
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>
> 



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