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

[Tom Wiltshire]

Jack's asked probably the first question of all. This would be my question to follow up:

Does the envelope work ok with the VCA, or are both the VCA and VCF showing the same symptoms?

The Juno 6 multiplexes control for the filter envelope, and if the VCA was ok, but the VCF was not, it might suggest a failure in the MPX/DMPX - 4051s, so not entirely unlikely.
If both VCA and VCF are similarly affected, and it affects all voices, that suggests that the ADSR CV generation circuitry on panel board B is screwed up - That's fairly basic, and in truth I'd expect that the most likely failure would be corrosion on the board connector between the panel board and the main board. Apply the usual treatments in this case - unplug it, scrape the connector pins with a small screwdriver tip to shift any corrosion, plug it and unplug it a few times, rinse and repeat as necessary until clean shiny metal touches clean shiny metal again.
However, you'll always get the odd ones where something more exciting gave up. Candidates in this case might be the op-amps that buffer the voltage before they go to the CPU board (1/2 of IC10, 1/2 of IC11, IC12), or (if they've all gone funny) the op-amp that produces the reference voltage for the pots (1/2 of IC9). All TA555385s. (?? Am I reading that right?)

If the problem doesn't affect all voices, then you're looking at specifics on the faulty voice/s, and I wouldn't expect it to be exactly the same issue on multiple voices.

HTH,
Tom

> From: synthesizerdiy at gmail.com
> To: jackdamery at hotmail.co.uk
> Subject: Re: [sdiy] Juno 60 woes
> Date: Wed, 10 Jun 2015 12:19:14 -0500
> 
> Since it seems you might have some intimate knowledge of the Junos at
> this point, would you happen to know where to look for an issue with
> the ADSR on a Juno 6? The release sliders does nothing and seems to
> output some release regardless where the slider is positioned. The AD
> seem to work and the S is questionable. I cannot find any position of
> any adjustment on the Synth to get any "R" to work or show any signs
> of life.
> 
> The synth has been fully recapped and cleaned. I have taken a look at
> the Juno 6 service notes.pdf and see that the slider for the "R" is
> VR12 and the amp IC should be IC11. Swapping IC11 had no change. I
> did however get the IC11 from UTSource.
> 
> Would you happen to know any area to look at to resolve this problem?
> 
> Thank you for your time,