First thing to do is check (with a scope) ICs 18 and 19, which provide
the demultiplexed signals for those CVs.
4051 CMOS ICs can become intermittently faulty over time; also, since
the two are connected to the same A,B and C lines, one bad chip can
affect the other.
~G
vib.ration33 wrote:
>
>
> Hello,
>
> I've been a P6 owner for about 15 years. The machine was thoroughly
> checked when I bought it, and the infamous battery was replaced before
> any damage got done. The machine has been in perfect order (except the
> pots have begun to have slight contact problems).
>
> Today when I decided to power it up again (the machine has been
> resting in the studio for a few months) it worked well for about half
> a minute or so, and then the cut-off pot ceased to have any effect.
>
> Interestingly the speed/intensity pot didn't work either. The weirdest
> thing is that now Envelope Attack pot actually acted like the
> speed/intensity pot, and Decay pot controlled the cut-off of the filter.
>
> All of the other pots in EG and EFFECT sections work ok.
>
> When I switched the machine on and off again, everything was again
> fine for a while. Besides of the little delay when the problems start
> the symptoms are at least that cut-off and intensity pots cease to
> work completely and other pots take their place.
>
> When in the problem zone the Attack and Decay pots have double
> function, they also control attack and decay besides cut-off and
> intensity.
>
> All of the other pots and switches work fine and the memory is ok. The
> intensity and cut-off values are recalled as they were.
>
> I just observed another interesting phenomenon: when tape is enabled
> MG Speed slowly ramps up to maximum speed. The ramp ends when tape is
> disabled. I can make this can happen before entering the problem zone.
> Sounds great (when modulating a resonating filter) but I don't think
> thats how it should work :)
>
> Another observation: the cut-off pot doesn't cease to work instantly -
> instead its range gradually diminishes (in 10-15 seconds) to zero.
>
> Any recommendations where to begin? Sounds like the synths is a little
> imbalanced, maybe a capacitor or resistor somewhere needs to be
> changed, or there is a creeping short-cut somewhere??
>
>
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