> I was wondering if somebody might be able to help suggest what to
> try here. One of the four ADSRs is broken in mine, the last one.
> The first thing I checked was the voltages present at the IC
> supply pins, and immediately noticed a problem. The +12V supply
> is present at the header and R15, but everywhere else appears as
> about -0.6V. So the TL084 and 555 and powered between -0.6V and
> -12V, or -0.6V and ground.
>
> Any ideas why the positive supply is like this

I'd recommend to trace the +12V from the bus connector to the mentioned pins
by means of a magnifying glass. Maybe the pcb track is interrupted anywhere.
Maybe near a pad that was damaged because of excessive force applied to the
corresponding electronic part. If the +12V are not present at the bus
connector the bus cable is probably damaged.

Best wishes
Dieter Doepfer