Weird problem with Juno 6

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cambodiamusic
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Weird problem with Juno 6

Post by cambodiamusic » Mon Nov 02, 2015 9:02 am

Before installing the cpu, I did some testing on my juno.
I found a problem.
All voices, all env, all filters works fine, keyboard cv works well, Lfo cv works

But the env amount to the vcf is not the same for all voices.
But the env amount to the pwm is not the same for all voices.

1 filter receives the right env cv amount but the other 5 receives a small portion of the env cv, like 50%. Same thing with the PWM.

Depending on how I play the voices, it varies. If I play 1 voice at a time, only the third voice receives the full MOD amount. If I play 1 voice, keep it, and then add a 2nd voice, and then a 3rd, all voices receives the full MOD amount only once I triggered the 3rd voice. The behaviour is exactly the same for Filter Env amount or Osc PWM amount from envelope.

I checked with a scope, all envelopes are fine, all filter are fine for LFO and Slider and Keyboard CV tracks perfectly for all voices.

I higly suspect the IC32 4051B chip, because all envelope goes in the chip perfectly, and because the output of that chip goes to Multi Env CV for the filter and for the PWM.

If you have an idea, I would thank you very much.

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tubbutec
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Post by tubbutec » Mon Nov 02, 2015 11:00 am

Hi,

thanks a lot for posting this question here in the forum. In case anyone else has the same problem with their Juno at some point, they might be able to find help here...

It is pretty awesome that you have an oscilloscope because it will make things so much easier.

As you already suspected it has probably something to do with the filter envelope multiplexing. Check the multiplexed envelopes at the output of IC32 on pin 3. You should see all the 6 envelopes here. Make sure they are all there with the right amplitude. They should also not interfere with each other.
If everything is fine here, check IC38, pin 1 (TP7). You should see the same thing here.

Next check IC47, the demultiplexer. measure at the outputs of Opams IC 46, IC44 and IC42. You should be able to see the individual envelopes here. If not IC47 might be broken, or there is dirt on the board making the sample and hold capacitors leaking.

cambodiamusic
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Post by cambodiamusic » Tue Nov 03, 2015 10:42 am

I measured all envelopes outputs on the scope and they all work perfectly. With sustain at maximum, it goes to 8V.

The 6 envelopes all reach the 6 inputs on IC32 perfectly.

However, the multi env out, (IC32 pin 3) is very weird.

I have attached here the output from the scope. I simply trigger one note at a time with the hold button ON. So you can see the 6 envelopes accumulating, but some weird voltage shift appear at some point, and you can clearly see that the voltage on the first voices is half what it is at the input of IC32.Image
Attachments
Multi env out of my Juno 6
Multi env out of my Juno 6
IC32 output.jpg (293.17 KiB) Viewed 449 times

cambodiamusic
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Post by cambodiamusic » Tue Nov 03, 2015 10:47 am

If I could compare with a working JUNO 6, it would be awesome.
Just display the pin3 of IC32 with the hold button and trigger 6 notes one after the other.

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Post by tubbutec » Sat Nov 07, 2015 12:33 pm

Hi didn't have the time to conmpare the waveforms with my Juno, but the waveforms do not look _that_ strange to me...

did you check the other things I proposed?

In any case you can replace the analogue switch ICs to see if there is any difference..

cambodiamusic
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Solved

Post by cambodiamusic » Wed Nov 25, 2015 2:41 pm

So my tech replaced the IC32 multiplexer and the problem was solved! He installed the Juno-66 CPU and everything works just fine. I tried the JUNO 6 last night... OMG! It's crazy! Live fatness control on a chord is simply awesome! Thanks for your support tubbutec!!

FlavioB
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Re: Solved

Post by FlavioB » Sun Dec 13, 2015 7:07 am

cambodiamusic wrote:So my tech replaced the IC32 multiplexer and the problem was solved! He installed the Juno-66 CPU and everything works just fine. I tried the JUNO 6 last night... OMG! It's crazy! Live fatness control on a chord is simply awesome! Thanks for your support tubbutec!!
Hi cambodiamusic - would it be possible to get some pictures of the MIDI outlets on your Juno-6?
Did you buy the additional "replacement panel" or how did you do it?
Thanks for your reply and kind regards,
Flavio.

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Post by Beeblebrox » Mon Nov 12, 2018 4:53 am

Just registered to say thanks for this (rather old) thread, I had been stuck with a similar problem then thanks to this found a broken trace between IC32 and IC37. All calibrated and sounding great now :)

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