Troubleshooting Jupiter 4 Voice card.

[jakobz]

Hi there
At the moment im trying to troubleshoot on a Jupiter 4, with 1 silent voice. Since i have 3 working voice cards, i think it should be possible to locate the issue. But i was wondering if anyone could offer some advice on how to proceed, since it is quite hard to do any measuring when the cards are mounted on the main PCB. Im thinking maybe making some sort of extension socket/cable so i can have the card connected outside the synth. But i would love to hear how people usually approach this.

 

[Bo Deadly]

First, swap cards to determine if it's really the one card. It could easily be a fault on the main board in which case swapping the cards should change the fault behavior (how precisely I don't know because I've never debugged an analog poly synth). Whatever the result, then I would start by just checking things with a DMM. Specifically, remove a good card and the bad card and check continuity between various points of lines that should be connected or have a known fixed resistance. You might get lucky and find a bad solder joint in which case you've saved yourself a lot of trouble. If that doesn't identify the problem, you might be able to just apply power to the board externally and sanity check voltages with a DMM.