[sdiy] Prophet 5 scale problem

[Adam Inglis]

I have a P5 here that seems to be working OK except that the lower ranges of the 2 VCOs for each of the 5 voices are randomly off scale/out of tune across the keys.

It seems to correspond roughly to a key CV lower than 3 volts with the VCO pitch pots at their mid-range (as evidenced by the CV out jack). Above this both VCOs track well in tune and scale. If I pitch both VCOs to their highest range, the top 4 octaves of the keys are in tune, just the lowest is out. Doing the inverse, most of the keys are out of scale except the top octave.
It does appear to be all 5 voices affected, so I’m having trouble narrowing it down to one chip, say e.g. a CV demuxer 4051, which are a common problem.

All 14 bits of the DAC are pulsing.

Further tests are obviously needed, but any clues greatly appreciated.

AI