Fixing JP-4/Promars ?

Stuart Robertson stuart at
Thu Mar 20 01:29:47 CET 1997

Anybody have any experience routing about inside either a Jupiter-4 or a
Promars ? (They are basically the same components)

I've got a Promars that I'm trying to repair but so far the fault has eluded me.

On waveform range 8 & 4, as well as the sub oscillator a strange beating is
occuring - looking at it on a scope it appears as it the VCO is retriggering
itself approx 30 degrees out of sync with the original waveform, causing a
sort of dischordant harmonic beating effect - sort of like a fuzz box just
before the batteries run out ; )

Also it appears with certain waveforms, and not others, but always the same
range positions - I suspect a 4016 analogue switch on the voice board to be
faulty, but I'm not convinced (and waiting parts).

Anybody recognise these symptoms ?


Stuart Robertson		
			stuart at
			101500.601 at
			stuart at

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