Troubleshooting Roland analog synthesizer's 'moving' dead notes

Question

I have a 1982 Roland Juno-60 'polyphonic' analog synthesizer.

Starting about 6 months ago it began having 'moving' dead notes.

What I mean by that, is that there is no evidence that any one key is 'dying' (or really evidence that any key is dying for that matter). The electronics overall usually seem ok.

What happens instead is that every 6th unique note that I play (or sometimes 4th or 5th) creates no sound. It comes across as being 'dead.' I can hit that note 500 times and it still will not produce a note. However, as long as I hit another 6 unique notes, that original dead key works again while my new 6th note no longer produces any sound when pressed.

This occurs in any pre-set voicing or even after heavy modification of the knobs/sliders. There is an arpeggiator button (auto arpeggiates all notes being pressed) that sometimes will force the 'dead' note back, but this has been very inconsistent.

My questions: What is causing this mysterious 'moving' dead note?? And How can I fix it??

I assume it's got something to do with some malfunction in sound wave production (vs. a strictly physical/electronic malfunction). But I really have no idea.

Any thoughts or expertise anyone can share would be most appreciated!

Answer 1

If it's anything like the archetypal polyphonic analog synthesizer (the Prophet 5), it has six analog voices (probably consisting of two oscillators, a low pass filter, and a couple envelopes each, and maybe more). Those six voices are not triggered directly by the keyboard. Instead, there's a microprocessor that allocates key presses to voices in a rotating fashion.

If one of your voices is dead, then every sixth key press (or so) would not make a sound. The "or so" is important. The algorithm in the microprocessor might not always go in precisely round robin order, depending on things like holding down a sustain pedal or certain envelope settings.

So, sadly, that's my guess - you have a dead analog voice. It's possible each voice is on its own PCB or daughter card so maybe replacing the card would fix it and be relatively easy.