The problem is usually at the CPU board, and is caused by battery-
leakage damage, just as you describe.
There are lots of board traces that run across the board and through
via-holes, and often I find that there is faults at the via-holes, and
also where baord traces cross board sides through IC legs. Sometimes
far from where the battery is.
I just had a P6 in with the same problem. Swapped out some 40xx logic
chips and repaired/strapped the traces, and the problem went away.
I often find several 40xx chips failing to pass (some of) the digital
control signals, and this can cause all kinds of strange behaviour
from major failures to tiny details.
Den 16. feb.. 2013 kl. 07.30 skrev klosmon:
> 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
>
Terje Winther
terje.winther@wintherstormer.nohttp://www.wintherstormer.no/[Non-text portions of this message have been removed]