Man, there's a good candidate for a clone board. 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? Has IC8 been removed, the area cleaned, and
replaced with a new socket and chip? You really are running out of
possibilities here.
Don B.
_____
From:
PolySix@yahoogroups.com [mailto:
PolySix@yahoogroups.com] On Behalf Of
klosmon
Sent: Saturday, February 16, 2013 12:38 PM
To:
PolySix@yahoogroups.comSubject: 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]
>
>
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