Troubleshooting tips for Juno 106

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Troubleshooting tips for Juno 106

Postby Jakobz » Thu Nov 29, 2018 9:27 pm

Hi.
I have a juno 106 with a very low hanging note, it is probably a voicechip going bad. I am pretty sure i know which one to replace, since i already replaced 5, and only have one original left in there. I could just replace it, but i would love to learn a little before i do so, so i was wondering if there is anyway i could find out exacly where the hanging note comes from, i suppose it would show up on a oscilloscope, or with an audioprobe if i know where to look. Both
the vca out and vcf out are laid out as testpoints, would the hanging note show up there?
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Re: Troubleshooting tips for Juno 106

Postby Mooger5 » Thu Nov 29, 2018 11:35 pm

it´s on page 18 of the serv manual. In test mode pressing poly 1 and poly 2 at the same time assigns the voices cyclically. The voice numberr appears on the display. The drone will change pitch according to the key that is pressed.

and the signal will appear at the test points, yes. dcos are always on, so when the filter is open a leaking vca will let the signal pass even when no key is pressed.
Herrare umanum est.
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Re: Troubleshooting tips for Juno 106

Postby Jakobz » Sun Dec 02, 2018 9:19 pm

Thank you very much, i will look into this.
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Re: Troubleshooting tips for Juno 106

Postby Jakobz » Tue Dec 18, 2018 10:00 pm

It turns out it is not a voicechip issue after all. I had the chance to try a complete different moduleboard, and the hanging note was still there. I suppose i should take af closer look at the cpu board, Is there any known issues that could cause this behaviour like leaking capacitors for instance?
Best regards
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Re: Troubleshooting tips for Juno 106

Postby Mooger5 » Tue Dec 18, 2018 10:38 pm

Is it like a humming drone, or a medium to high pitched whine?

Low pitch could mean bad PSU filtering due to ageing caps.
Higher pitch is, from experience, usually the wire looms that need to be rearranged...
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Re: Troubleshooting tips for Juno 106

Postby Jakobz » Wed Dec 19, 2018 9:19 pm

Medium to highpitch i would say. Interesting with the wiring, i will look into that.
Thanks!
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Re: Troubleshooting tips for Juno 106

Postby Jakobz » Wed Dec 19, 2018 11:19 pm

I tried moving the wiring carefully around, but it did not seem to affect the sound. i tried to make a recording of it.

Hanging note
It is affected by chorus and waveform. Also i noticed The led for chorus 1, has a dim glow when turned off, What could be causing this?
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Re: Troubleshooting tips for Juno 106

Postby Mooger5 » Thu Dec 20, 2018 1:58 am

The volume is set quite high, right? As the sound is just a tad above noisefloor. Anyway, the pitch is very steady, so it could still be related to the PSU. Notice the lower "fundamental" tone. The rest comes after rectification. Poor filtering or poor regulation. I´d check the solder side of the PS, starting with the regs.


Before that, inspect every connector for weak joints. When replacing voice chips there´s always a lot of plugging/unplugging.

It could also be a CPU that is about to die, ugly scenario.

If the PSU is outputting the right voltages with negligible ripple, then an AC coupled (always) audio probe would come handy.

My 106 has an LED like that too There are maybe fewer Junos in the world that don´t have it. It could be electromagnetic induction caused by the power transformer sitting underneath. I believe there is no cause for alarm.
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Re: Troubleshooting tips for Juno 106

Postby Jakobz » Thu Dec 20, 2018 7:53 pm

Yeah it is quite low, and not really a problem until you know it is there :) Thanks for your advice, i will take a look tonight :)
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