What's Wrong With My Juno-106?

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Lester Drek
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What's Wrong With My Juno-106?

Post by Lester Drek » Mon Mar 20, 2017 2:58 am



I acquired a Juno-106 recently that I believed to have voice chip issues. There is a rattling, rhythmic pulse that occurs on some patches.

However, I did the voice test, and I really can't hear anything wrong between the voices. When I tested the Freq with the Res at 10 and Freq at 5, the same note played for voices 1-3 sounded the same, but 4-6 each were their own different pitch. But I read that's supposed to happen and not really an indicator of a failing chip.

Does anyone have any idea what could cause the rattling, failing voice chip sound when all my voice chips sound fine when I test them?

Another note: When I go to Group B in the voice testing, each voice sustains and doesn't sound right, but I'd assume because that's not the normal way to test the voice chips? Or should they sound like they do in Group A?


Thanks for any help.

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Re: What's Wrong With My Juno-106?

Post by madtheory » Mon Mar 20, 2017 1:44 pm

Post an audio example. "Rattling" is a pretty subjective term.

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Re: What's Wrong With My Juno-106?

Post by Lester Drek » Tue Mar 21, 2017 5:51 am

Here's a sample: https://soundcloud.com/playertwoatl/juno-106/s-BIEq5

Notice the distortion on the last patch; this isn't clipping.

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Re: What's Wrong With My Juno-106?

Post by cornutt » Tue Mar 21, 2017 4:16 pm

Are you talking about that rapid tremolo in the fourth one?

That crackling in the last patch comes from overdriving the input to the chorus. Turning the VCA down a bit will take care of that.
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Re: What's Wrong With My Juno-106?

Post by Lester Drek » Tue Mar 21, 2017 9:37 pm

cornutt wrote:Are you talking about that rapid tremolo in the fourth one?

That crackling in the last patch comes from overdriving the input to the chorus. Turning the VCA down a bit will take care of that.
Yes that was tremolo actually. BUT, there is this other rattling and like arpeggiator thing happening. This happens when I turn up the res on some patches.

https://soundcloud.com/playertwoatl/jun ... ds/s-uTQas

The first patch in this sample I am just going up the scale.
Last edited by Lester Drek on Tue Mar 21, 2017 10:03 pm, edited 2 times in total.

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Re: What's Wrong With My Juno-106?

Post by Lester Drek » Tue Mar 21, 2017 9:51 pm

https://soundcloud.com/playertwoatl/jun ... st/s-7XVR0

The freq/res voices for 4,5 and 6 sound way off. Should they all sound like 1,2,3?

https://soundcloud.com/playertwoatl/jun ... -b/s-4LZSx

Is Group B supposed to sustain like this?

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Re: What's Wrong With My Juno-106?

Post by cornutt » Wed Mar 22, 2017 6:06 pm

Can't get to Soundcloud right now from work, will try again this evening.

A patch stored in Group B should sound exactly like the same patch stored in Group A; there's nothing different between the two groups. Try recalling a patch from Group A, writing it to a location from Group B, and then comparing the two. They should sound identical. If not, something is going on with the patch memory.
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Re: What's Wrong With My Juno-106?

Post by Lester Drek » Wed Mar 22, 2017 7:52 pm

cornutt wrote:Can't get to Soundcloud right now from work, will try again this evening.

A patch stored in Group B should sound exactly like the same patch stored in Group A; there's nothing different between the two groups. Try recalling a patch from Group A, writing it to a location from Group B, and then comparing the two. They should sound identical. If not, something is going on with the patch memory.
Thanks for the reply. I can write patches from A to B and they sound identical. I was speaking about in test mode, Group A voices sound fine, but when I switch to Group B, every note I hit sustains no matter where I set the release.

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Re: What's Wrong With My Juno-106?

Post by Mooger5 » Thu Mar 23, 2017 6:35 pm

The sustaining is normal. In test mode, Group A = holf off, Group B = hold on. For servicing the board without having to press the keys all the time.
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Re: What's Wrong With My Juno-106?

Post by Lester Drek » Thu Mar 23, 2017 11:18 pm

Mooger5 wrote:The sustaining is normal. In test mode, Group A = holf off, Group B = hold on. For servicing the board without having to press the keys all the time.
Ok thanks. What about the off tune voices in the res test?

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Re: What's Wrong With My Juno-106?

Post by Mooger5 » Fri Mar 24, 2017 12:26 am

The VCFs need calibration.
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Re: What's Wrong With My Juno-106?

Post by Lester Drek » Fri Mar 24, 2017 1:59 am

Mooger5 wrote:The VCFs need calibration.
How do I do this? I quickly googled an saw a video using an Oscilloscope, which is hundreds of dollars that I don't have.

Is there another way to do this? Can I replace the VCF chip(s)? This is my first synth hardware repair so please excuse my lack of knowledge.

Thanks so much for the help.

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Re: What's Wrong With My Juno-106?

Post by Mooger5 » Fri Mar 24, 2017 1:34 pm

Replacing the chips still require calibration aftwerwards. And well, there are used analog scopes for under 100 if you shop around. Anyways, you don´t really need one to calibrate just the VCFs, if everything else is behaving correctly. A digital multimeter and a tuner are enough.
But it´s no easy feat for the inexperienced. It requires a certain know-how and a lot of patience. I sincerely suggest you ask someone familiar with electronics to do it for you. The Service Manual is @ synfo.nl and you can follow the series of videos by Syntegrator

Good luck.
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Re: What's Wrong With My Juno-106?

Post by Mooger5 » Fri Mar 24, 2017 2:12 pm

Or maybe I´m being overzealous. If the resonance is OK on all of the voices, then hopefully it´s only the filters´cutoff adjust pots that are slightly off. I´ll get back to this in a few hours.
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Re: What's Wrong With My Juno-106?

Post by Lester Drek » Fri Mar 24, 2017 6:30 pm

Mooger5 wrote:Or maybe I´m being overzealous. If the resonance is OK on all of the voices, then hopefully it´s only the filters´cutoff adjust pots that are slightly off. I´ll get back to this in a few hours.
Did you listen to my res test sample? The tones for 4-6 are each WAY different than the 1-3. So what does that mean? I think the filter's cutoff adjust pots being off is right. I'll try to upload some more samples so you can hear it. There's definitely something going on with the VCF, that's the garbled, almost arpeggiating-like sound I was talking about. You hear it best on the very first sample I posted.

https://atlanta.craigslist.org/nat/ele/6006462749.html

Would this oscilloscope suffice? Also, I think you're right about it needing calibration. I was recording the other day with it and it sounded out of tune to my guitar, but I'm going to do some more tests to confirm. Is the oscilloscope for tuning the synth? What is the multimeter for?

Thanks again for all help thus far.

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