[sdiy] Juno 6 woes (was Juno 60 woes)

Tom Wiltshire tom at electricdruid.net
Fri Jun 12 10:03:37 CEST 2015

On 12 Jun 2015, at 06:13, synth <synthesizerdiy at gmail.com> wrote:

> I cannot get the "R" to work on anything.  I have cleaned up the unit and plugged/unplugged everything before.  Is there a certain connection you would suggest focusing on?  Or is there some part ID numbers that you could suggest looking at and testing?
> Page 13 of 16 in the service notes shows slider VR12 100k to be the "R" and that goes to the TA75558s IC11 which I have tried swapping out and through R118 (39K).  From there it goes to connection 11 CPU Board to connection 27 Release voltage.

Ok, that seems pretty clear. If the release isn't working anywhere, we need to follow it through from the slider, like you've done. You didn't mention whether you'd checked the release voltage is ok. It should read 0-5V as you move the slider.
You can get it either at the slider wiper, or (better) after the buffer on pin 2 of IC11 (the op-amp) on Panel Board B. The op-amp looks like it's in a weird flat 9-pin package, and you can get the buffer output on the jumper wire J10 above it. You could check with a multimeter, but if you've got a scope, I'd have a look with that too, just to see that there's no wild noise lurking there that you wouldn't see on a multimeter.
After that, it goes to the connector. It looks like "11" is the pin at the Panel Board B end, and "27" is the pin at the CPU board end. Check the voltage again at the CPU board end. Wiggle the slider and check it still goes from 0-5V. I expect it doesn't, because if it did, it should be working!

> Since the A and D work I can assume that nothing past this point is the problem, correct?

You can probably assume that the Envelope chips themselves are ok, so you need to make sure the Release CV gets all the way to them.
> Following connection 27 Release Voltage to page 9 of 16 I see it going/coming from the ENV Time section.  Looks like that divides into sections and heads to a 22K R53 then to the IR3R01 IC Pin  4.  These IR3R01 ICs show to be IC26-31.

Yes, correct. Check for the release CV at the connector and then at the 22K for each chip if it's still ok at the connector.

> This is where I would say I am lost on the matter.  It looks like the ADSR is controlled by these ICs.  One IC per channel.  Where is the signal controlling all of these 6 ICs coming from and what would I look at to isolate my issue with the "R" not working and being "stuck" on?

The IR3R01s are the voltage-controlled envelope generator chips, so yes, the ADSR is "controlled" by this chip - I'd have said "generated".
The envelope outputs are then multiplexed and mixed with the other filter control voltages, but if this part was faulty, I'd expect it to affect all stages, so I think a failure in the Release CV before the ADSR chips is more likely at this stage.

> Thanks again for looking at this problem with me,

You're welcome. Good luck.


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