Thanks -- will keep checking.
~G
On 2/16/2013 12:10 AM, Terje Winther wrote:
> 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
>>
>