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
>
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>
>
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