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Jupiter 8 repairs
 
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I bought my dream machine back in 1994 or so. I absentmindedly wandered past it sitting unloved in the back of "Musician's Pro Shop" at Mermaid Beach. It was on consignment, with a price on it of around AUD$700 or so, as I recall. It looked a sorry sight, covered in scratches and scars, with rusted screws. Apparently it had belonged to a hard-touring aussie band during the eighties. It looked "heavily gigged", as they say.

Yet, as I looked at its rainbow of buttons and bright orange labels, a dim memory was surfacing. "A Jupiter 8.. hmmm, why do I know that name? Wasn't that once a big deal?". I had murky visions of nameless gigs at the Playroom, where some band's keyboard player, with the ubiquitous spikey haircut, stood behind a big synth sporting an orange pilot light, and the word "Roland" in white letters across the back.

Finally I remembered. When I had been falling in love with synth music, this synth had been the queen. Especially in 1982, its sound was everywhere.

"It's got MIDI" the salesman said hopefully, and held up one end of a cable that definitely was NOT a MIDI cable. I found out later it was a DCB cable. Unfortunately there was no converter box to accompany it.

Anyway, it sounded incredible... and all those controls! It made those string pads I had always lusted after. There weren't too many problems with the electronics - in fact, it just needed re-calibrating, and one oscillator was "sour". Darryl Watson, the Brisbane Roland tech, sorted that out for me, and after that she sounded as good as new. Shame about how she looked...

These days, I fix the Jupe and most of my other vintage gear myself, having picked up some synth electronic know-how and wisdom from textbooks and generous people around the internet (assisted considerably by a multimeter, oscilloscope, and a desoldering gun).

I've noticed a couple of problems keep cropping up from time to time with the JP8. One is the "sour" VCO trouble, where the VCO just won't be tuned, although it is not out by a great margin, but enough to annoy. The other thing I've seen a few times is a problem with the selection of the waveform. A particular waveform will be absent or quiet, or just not sound the way it should.

The first problem is not on the VCOs PCB as you might first think, but further afield, over on the "Interface" board, that contains the DAC and the sample and hold circuits that control each VCOs pitch CV. A dual op-amp (TL082) buffers the hold capacitors for two adjacent channels, and somehow when this chip gets faulty the pitch CV going to one or both VCOs gets unstable. The fix is to replace the op-amp.

Above: the eight dual op-amps for the pitch CVs on the Interface board. Two are sitting in sockets.

 

The second problem I've found to lie with the waveform selector chip, a 4052 analogue switch. These chips can develop faults on one or more channels, causing a quiet voice, or wrongly selected waveform.

Above: the waveform selector 4052 chip on one of the VCO voice PCBs.

 

 

 

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