Juno 106 Repair Advice

Hello! I’m basically brand new to the Syntaur Forums but have been following the YouTube channel for a little over a year and a half now. I figured this would be a good place to ask for good advice on my new Juno 106.

I picked up a Juno 106 yesterday that needs a little bit of love and wanted to see if anyone could help me diagnose the issues. It’s the first analog synthesizer that I’ve ever owned, and I want to get it back up in good shape. I have basically no experience in soldering, but I’m hoping to learn and have friends who are adept enough to be able to push me in the right direction or show me how its done, but they’ve never worked on a Synthesizer before.

It works for a little while, maybe about 5 or so minutes at most, then it begins to show some issues. The main issue that I’m facing with it is that I am getting a crackling out of the main audio outputs, both L/R and the headphone ports, and the chorus seems to bring out that crackling a lot more, in addition to having a single note, usually the 6th note played in a 6 note sequence being held out despite the release slider being all the way down and no notes being pressed on the keyboard. Some buttons need to be replaced as well, namely Chorus II, 2/3 Octave Shifters, and Numbers 4 and 5 in the bank buttons, but I’m more concerned with the crackling. Are the voice chips the things that I need to take a look at or do I need to look at replacing some of the ICs?

One thing I also tried was turning the chorus off, sometimes that prevented notes from being held and having less crackling; however, in some cases even having the chorus off cause a note to be held out very faintly.

From when I’ve messed around with it, it doesn’t seem out of tune, it’s only that the crackling comes after a little while.

I was able to look at the CPU Board and the Power Board, but I haven’t been able to get into the panel board yet.

Had that same issue with my 106, crackling and such. Most likely culprit is the voice chips like you said. You may already know this but the 106 voice chips are coated with an epoxy that becomes conductive, causing issues with the chip and leads to malfunction. It’s the number 1 issue people have with this specific synth. Inside each voice chip is a VCA and VCF, so crackling/stuck notes/filter issues is a telltale sign a chip is malfunctioning.

Instead of buying a whole new set of vintage or clone chips, find out which voice is having the issues. To do so, you’ll have to put your Juno in a diagnostic mode, which you can find how to do so here: http://www.analoguerenaissance.com/JUNOTEST/

Go through the test and find out which number voice or voices need replacing. Some chips can be salvaged by removing the chip and soaking it in pure acetone for 3 days. The acetone softens the epoxy which you then carefully peel or scrape off.

If you replace the bad voice chips i’m fairly confident you shouldn’t have any issues with your chorus, but if it doesn’t you can replace the BBD chips with modern identical sounding chips (two in total) for about $25. You can find these replacements here: https://cabintechglobal.com/mn3009

Good luck.

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Thank you for your advice.

I went through the test and was able to find some new information.

The DCOs seem to be alright, the only things that worry me are the VCAs and the VCF.

It looks like all my voices were pretty well out of tune when it came to the Filter test.

I may need to replace all of them, but I will try the acetone method over the next week when I have the chance to see if that improves them. If not, I’ll go with the analog renaissance remakes.

The only other thing is that some buttons do not work or are unable to be pressed, I imagine I’d just need to do a cleaning on those after getting a good look at the panel board. The other thing I noticed is that the high pass filter could also be broken, or at least the slide pot for it.

Edit: I realized that I was unable to press the Poly 2 button, so I may need to do further testing to be absolutely sure.

You will likely find that the VCA/VCF chips are the first to go. You may have luck with the acetone dip, but usually you can save a lot of trouble by just replacing them with the Analog Renaissance chips sold on Syntaur. They sound practically identical to the originals, plus seem to be more reliable.

Also, you might also find that the L/M/H volume switch on the back of the unit could be a source of intermittent/crackly output. It almost always could use a little shot of cleaner. Give it a blast with some cleaning juice, then work it pretty good for a couple seconds.

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