Vintage Synth Explorer Forums

I was playing my Jup 6 last night and noticed something weird. At first I thought the key assignment was acting funky but upon further listening I discovered that every 6th note is almost inaudible. I began thinking that maybe one of the voices just had a lower volume than the others but it didnt change if I adjusted the balance knob for the 2 VCO's. Then I tried moving the filter cutoff slider and the voice began to crackle and pop, very similar to how a Juno 106 sounds when a VCF chip is failing.

I pressed the tune button and found that it is voice 6 that is affected, and I can reproduce the failure every time. Are these boards known to fail like the Juno's do? Im really bummed here, I just bought this board about 3 weeks ago. This fault may have been present when I received it but just now noticed when I got more time to fiddle w/ it.

I have yet to open the synth up, im hoping the IR3109 chips are in sockets so I can try swapping two around. I may try that this evening, if anyone has any input id greatly appreciate it.

Thanks

Well the IR3109's aren't in sockets so I wont be able to easily swap them, c**p. Anyone know which voice is which on the PCB? There are 4 voices on one board and 2 on another, but they're both labeled the same.

Also looking at these guts, I wonder if anyone has tried populating the rest of the empty voice sections to make an 8 voice Jup 6...

I am by no means an expert but I like to dabble. Some ideas.
- Does the issue persist when filter modes are changed? LP/HP/BP....looks like there is one chip for each LP and HP and when used together creates a bandpass circuit.
- Check DC voltages on the power supply. I've seen errant voltages cause very specific issues before.
- Maybe the data bus for that voice has an issue that is garbling the filter.
- Maybe the cutoff or resonance is out of adjustment. Looks like they can be calibrated using the scope.
- I'm not sure how to suss out which voice is voice-6 but the schematics would lead me to believe it's on the 2-VCO module board (that is, assuming voices on the 4-voice board 1-4 are A-D). If that's the case then perhaps the VCF on the 2-voice board is 'B' if the VCOs are A1/A2 (voice 5?), B1/B2 (voice 6?).
- So finding the affected voice circuit is the key to troubleshooting, and ruling out the other possible issues listed above first. Then if you are confident w/ your de-soldering skills I would go ahead and pull the VCF chips for the affected voice and a good voice, and solder in some sockets so you can do a swap between voices.
- When it comes to the Jupe there's no shame in taking it to a qualified synth tech for some peace of mind.

EDIT: oh and I probably wouldn't want to populate the 2-voice board without some engineering. 1) Additional circuits require additional power 2) don't know if the data system is set to manage 8-voices and might confuse the CPU. But yes, the possibility is quite intriguing!

Thanks for the lengthy reply, I'll try some of those tonight and see what I come up with. The part that is kind of bothering me is the fact that this synth was supposedly gone over by a tech in NY before I bought it and they gave it a clean bill of health. So either that tech didn't know what they were doing or it flat out wasn't really taken to a tech. Both possibilities bother me as I paid top dollar for this synth.

Not sure if you had it shipped to you but that process can be brutal on synths no matter how well packed. Wouldn't surprise if there's a solder joint or connector plug that can easily come loose w/ vibrations and impacts during shipping.

garranimal wrote:Not sure if you had it shipped to you but that process can be brutal on synths no matter how well packed. Wouldn't surprise if there's a solder joint or connector plug that can easily come loose w/ vibrations and impacts during shipping.

Im assuming this is my problem, I was playing the synth problem free last night for a couple hours. I think the movement from my stand, to the desk and back to the stand maybe wiggled something back into place. Ill leave it be for now..

sqweebking wrote:

garranimal wrote:Not sure if you had it shipped to you but that process can be brutal on synths no matter how well packed. Wouldn't surprise if there's a solder joint or connector plug that can easily come loose w/ vibrations and impacts during shipping.

Im assuming this is my problem, I was playing the synth problem free last night for a couple hours. I think the movement from my stand, to the desk and back to the stand maybe wiggled something back into place. Ill leave it be for now..

Hope it keeps behaving well!

I have a similar problem with my Jupiter 6 , though it is intermittent.
I always thought it was an oscillator failing, as when I play certain notes there is no sound, yet when I put it into 'solo' or 'solo unison' it works fine on all notes.
This suggests a faulty oscillator connection to me rather than filter. I must get it in for a service, but I dont want to be without it & I think it will need to go overseas ( to the UK , probably Tony Allgood of Oakley Systems as I have spoken to him & he is familiar with the J6 & also does interesting mods for the J6 , not Europa..)for a professional service.
Costly business with shipping on top but it would be great to get it working perfectly after putting up with this fault for years now. Its fine most of the time though , which is why I tolerate it.

garranimal wrote:Not sure if you had it shipped to you but that process can be brutal on synths no matter how well packed. Wouldn't surprise if there's a solder joint or connector plug that can easily come loose w/ vibrations and impacts during shipping.

This happened to my DK-600. Packed infinitely well by pros, but a huge resistor managed to fall out in transit. Pretty weird.

Had the exact same issue, it's unlikely to be the chip. Get those orange dipped caps swapped out, they fail intermittently. I replaced all mine with Mylar 5% (the originals are 10% dipped ceramic). Recalibrated as per service manual, crackle gone. I also retrobrighted the slider caps and buttons, it's like having a brand new Jupiter 6.

Thanks for the suggestions, the synth has been working on an off over the years. Its currently in its defunct state, I'll revisit its health once I'm done building the TTSH v4 kits I'm currently working on

I had a similar issue where one of the legs of the IR3109 had a cold solder joint and made one of the voices fail intermittently. Adn while you are at it maybe get a socket in there and desolder 2 of them so you can swap them around?
They take a bit of heat and seems to be quite sturdy. I socketed all my IR3109 and CEM chips on the boards with no problems. Used a desoldering station.

Another error that showed up on my Jupiter 6 and that made one of the voices very low in volume and also strange when using the filter, was that one of the analog switch IC's for the filter MC14551B had failed with one of the switch paths in an open and one in a closed position therefore messing up that voice.

Also a problem could be the 5218 opamps around the 3109.

Lektroid wrote: ↑

Wed Oct 30, 2019 4:00 am

Had the exact same issue, it's unlikely to be the chip. Get those orange dipped caps swapped out, they fail intermittently. I replaced all mine with Mylar 5% (the originals are 10% dipped ceramic). Recalibrated as per service manual, crackle gone. I also retrobrighted the slider caps and buttons, it's like having a brand new Jupiter 6.

Sorry for the necro but I wanted to provide some closure to this thread...

Thanks for the suggestion Lektroid - I found the same suggestion on this Gearspace thread and ended up replacing the orange polystyrene caps in the VCO and VCF sections. So far so good, I haven't encountered the "dying" voice/filter issue or the Europa F6 boot code since. Fingers crossed it stays that way

I've documented my repair a bit more on my personal blog here if anyone is interested. https://mikeder.net/blog/jupiter-6-repairs-2022/