Juno-106 Restoration story/Power Supply woes

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Yekuku
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Re: Juno-106 Restoration story/Power Supply woes

Post by Yekuku » Wed Feb 06, 2019 7:37 pm

So it was IC1! I wish i had such luck with my own repairs...
What about the bender's range issue?
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Re: Juno-106 Restoration story/Power Supply woes

Post by The LT » Wed Feb 06, 2019 8:15 pm

Yeah, thanks for the tip, Yekuku. As you can see, I am not that lucky with my second unit. :) Everything on it was dead.

Anyways, I've cleaned the rest of the chips and all of them finally work. I've run through the calibration and the unit at least plays now.

During calibration I ran into another issue. I cannot get PWM duty cycle on note C4 to 50%. It will only go to 27% and less. On C3 and lower, it's at 50%. I can hear this. I've tried reseating the wire looms, nope. BUT! When you briefly play a higher note and then get back to C4, I get proper 50% duty cycle which quickly (less than a second) jumps back to 27%. Op-amp issue?

Other than that, everything checked out during calibration. VCF response and VCAs work properly on all channels.

The bender assembly was totally replaced on Unit #2. All three bender faders were installed new from Syntaur. The range is low on all three paramters. VCF bender range is low too. It's less than a half of what it should be.

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Re: Juno-106 Restoration story/Power Supply woes

Post by Mooger5 » Wed Feb 06, 2019 9:04 pm

The PWM issue sounds like the DAC isn´t properly adjusted. It must be calibrated prior to PWM, and the keyboard must not be touched or it will set a different bias.
Other than this, see if there´s anything wrong with the Subosc, as they share the same dual opamp.
C66 is the S/H capacitor. An undervalued cap or a bad joint could probably be a cause as well.

BTW I didn´t say Your eyesight was bad or anything, it was a way of saying I wasn´t wearing my glasses, and there could be a similar reason for your tech´s mistake. I can´t think of any other reason for a tech to do that deliberately other than sabotage...
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Re: Juno-106 Restoration story/Power Supply woes

Post by Mooger5 » Wed Feb 06, 2019 9:09 pm

Also check for -15V on r116...
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Re: Juno-106 Restoration story/Power Supply woes

Post by The LT » Wed Feb 06, 2019 9:45 pm

Mooger5 wrote:The PWM issue sounds like the DAC isn´t properly adjusted. It must be calibrated prior to PWM, and the keyboard must not be touched or it will set a different bias.
Other than this, see if there´s anything wrong with the Subosc, as they share the same dual opamp.
C66 is the S/H capacitor. An undervalued cap or a bad joint could probably be a cause as well.

BTW I didn´t say Your eyesight was bad or anything, it was a way of saying I wasn´t wearing my glasses, and there could be a similar reason for your tech´s mistake. I can´t think of any other reason for a tech to do that deliberately other than sabotage...
Sorry Mooger5, I didn't want to upset you. :) You're totally right about being careful and observant. It's just this whole second 106 that was so f**ed up that nothing suprises me anymore. A lot seemed like sabotage on that unit.
Image

I've done the DAC adjustment and zeroed it out. Boot into testmode, press MIDI CH button, check module board TP3. Reads a perfect 0.00V. You know, maybe it's just the way Analog Renaissance chips work? Sub-oscillator works as intended. Weird... Initially, when I am rotary testing on C4 Test Bank 5 is 50% if I "reset" it with a high note (C6). But it quickly jumps back to 27% on all 6 voices when I start banging on C4 again.

R116 has -14.92V. I've changed IC8 op-amp and C66 but nothing changed. Same behaviour.

I've noticed a pattern. When I test PWM in rotary mode (POLY1+2), if I hit a high key first, then start testing voices from 1 to 6, they check out with 50% PWM, but as soon as the cycle ends (I walk through 6 voices) and I reach the 6th voice in sequence, the PWM quickly shifts from 50% to 27%. It's even seen on the scope and heard too.

Here is a small video.
Last edited by The LT on Wed Feb 06, 2019 10:50 pm, edited 2 times in total.

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Re: Juno-106 Restoration story/Power Supply woes

Post by Mooger5 » Wed Feb 06, 2019 10:48 pm

Now that you mention, with the DAC properly calibrated, the PWM CV should be steady and common to all notes. Any influence the pitch should have over the width of individual notes must be happening at the core of the waveshapers. It´s true the 5532 aren´t as easy to clone as the 80017. AR could have cloned the Juno 60 circuit instead, because the schematics are well detailed in the sm and maybe missed out something specific to the 106. But I´m speculating here. Were there any reports by other users?
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Re: Juno-106 Restoration story/Power Supply woes

Post by The LT » Wed Feb 06, 2019 10:51 pm

Mooger5 wrote:Now that you mention, with the DAC properly calibrated, the PWM CV should be steady and common to all notes. Any influence the pitch should have over the width of individual notes must be happening at the core of the waveshapers. It´s true the 5532 aren´t as easy to clone as the 80017. AR could have cloned the Juno 60 circuit instead, because the schematics are well detailed in the sm and maybe missed out something specific to the 106. But I´m speculating here. Were there any reports by other users?
Please see my video above. I can throw the original 5532s from the first unit in, but something tells me this is something else.

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Re: Juno-106 Restoration story/Power Supply woes

Post by Mooger5 » Wed Feb 06, 2019 11:10 pm

You mean opamp IC18? The quarter part of IC18 in that circuit is the S/H, just after C66. The opamp that drives the PWM is one half of IC17, the other half used for the Subosc. If they´re working for the lower notes, then it´s working for the other notes as well. Culprit elsewhere, as explained above.

One way to find out: at 50% duty cycle it must measure +6VDC at the junction of C63 and R119. While playing ANY note. It must also read the same on pin 12 of every waveshaper.
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Re: Juno-106 Restoration story/Power Supply woes

Post by Mooger5 » Wed Feb 06, 2019 11:18 pm

Just saw the edit. I get it now. Could have to do with the counters or something surrounding the waveshaper. Try to identify which 5534 the note pertains to. Then compare with the other waveshapers.
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Re: Juno-106 Restoration story/Power Supply woes

Post by The LT » Wed Feb 06, 2019 11:32 pm

Just tried a 5534 swap from Unit #1. Same behaviour. This happens exactly after 6 presses of the C4 key. No particular 5534 to tie this to. Replaced IC17 just for the heck of it. No change. :)

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Re: Juno-106 Restoration story/Power Supply woes

Post by Mooger5 » Wed Feb 06, 2019 11:53 pm

If it´s every 6th note then it must be always the same voice, no?
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Re: Juno-106 Restoration story/Power Supply woes

Post by The LT » Thu Feb 07, 2019 12:24 am

Mooger5 wrote:If it´s every 6th note then it must be always the same voice, no?
Not really. When POLY1-2 are enabled, I can rotate to, say, voice #3 and then hit the high note. The the PWM reset will occur on the next voice #3 activation, i.e. after 6 presses of C4. No matter the starting voice number, it always occurs after 6 triggers.

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Re: Juno-106 Restoration story/Power Supply woes

Post by Mooger5 » Thu Feb 07, 2019 1:03 am

I see. I´m beginning to suspect that it´s something intrinsyc to the design of the 106. A quirk related to how all the voices are "hardsynced" to the master oscillator. Can´t remember the exact word atm. Part of the reason why the unison never sounded as useful as say the 60 or the Polysix.
Is it noticeable when playing a PWM strings patch, for example?

I may try looking at the schematics tomorrow if I find the time.
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Re: Juno-106 Restoration story/Power Supply woes

Post by The LT » Thu Feb 07, 2019 1:11 am

Hmmm. Not sure why the other unit doesn't have it? And swapping the waveshapers does not help. This isn't exactly audible per-se, but I hear differences between the patches that use PWM. The maximum PW also goes higher and almost to 0% duty cycle. After all I've been through, I just can't stop there. :)

Maybe swap the 80017A/5534 sets around? See if the issue is with them? I would appreciate it if you could take a look. I am stumped.

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Re: Juno-106 Restoration story/Power Supply woes

Post by The LT » Thu Feb 07, 2019 6:51 pm

I've localized the bender problem to the bender potentiometer itself. I've swapped the bender assemblies between the units. The VR3/4/5 sliders check out fine.

It seems the pot range is wrong. The original pot goes from 44k straight to 0 ohms on maximum deflection. The new syntaur pot goes to 47k to 38k on the required range. It also has a bit more travel than the original. Original is little above 180 degrees and replacement is close to 200. Looks like it's not a drop-in replacement after all.

Damn.

I've ended up disassembling the original pot and, what do you know, the previous "tech" assembled it incorrectly. I've relubed, cleaned and reassembled it and now the bender board works properly.

Now the last issue to tackle is the PWM problem.

EDIT:

I am actually coming to the conclusion that this PWM problem isn't that much of an issue. When not in test mode, the PWM works as it shout. 50% duty cycle at the lowest levels on all voices/poly modes.
Last edited by The LT on Thu Feb 07, 2019 9:40 pm, edited 1 time in total.

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