I've acquired a Jupiter 4 synth quite recently. Seems in pretty good nick, only problem I have is that when you play a note the sound seems to sustain permanently even when you release the key. The effect is very similar to having a hold pedal plugged in. Have tried messing with the envelopes etc with no joy.
Other than that the synth seems to work fine. I'm keen to sell this so just wondered how easy it would be to fix?
If the presets sound fine without sustain then it is probably a problem with the VCA Release slider.
If presets are also sustained then it can be an envelope generator malfunction on the Module Controller.