Juno 60 - Envelope doesn't apply to one voice

[mediocrates]

I have a Juno 60 with a strange characteristic. It seems that one of the six voices is not properly responding to the envelope. The Attack is appropriate, but it seems to get hung up on the sustain. Here's a sample of what it sounds like:



So, if I turn the machine on from scratch, and begin hitting notes on a scale, the 3rd note I play consistently displays this problem. This seems to suggest that something is wrong with a specific voice?

Note: I installed the following CHD Midi kit about three years ago. It doesn't seem related, as the problem I've described only started about 3 months ago.

http://www.chd-el.cz/index.php?id=468&lngid=en

Any help greatly appreciated.

Thanks,
Anthony

[funkpirateradio]

Try the Juno 60 test procedure here http://www.retrosound.de/junoservice.htm and figure out which voice is causing the trouble.

I'd guess that the IR3R01 envelope generator IC for that voice would be at fault.

[mediocrates]

So... I replaced the #3 VCA chip. It was BA662 209 B. I replaced it with an A series chip (BA662 509 A - i think). The problem persists.

--> Here's a video of the problem <--

Some observations:
1) when I first turn it on after having been off for a while, it is silent, but slowly (over the course of 30 seconds or so) the hanging voice gets louder and louder. This is without having yet played any notes.

2) When I close the filter (bring frequency all the way down) but keep the ENV setting at max, I can play the notes without hearing the hanging note, but as soon as I open the filter back up, the hanging note comes back.

I'm looking at the block diagram from the service manual, but am just not sophisticated to figure this out.



Does anyone have any suggestions? I can order and swap out ICs but I don't know which one is the source of the problem...

I'm stumped...

Anthony

[HideawayStudio]

Hi Anthony,

In most analogs the oscillators are never disabled (even DCOs) and will therefore be set to either their default pitch or the last pitch the note assigner allocated. Thus it sounds very much like one of your VCAs is permanently open as by moving the cutoff to the zero position you are basically masking the effect.

If you have changed the VCA itself to no effect then I suspect either the VCA IC in question is not receiving a control voltage (or it is not in the correct range) or one of the six IR3R01 envelope generator ICs 26 thru 31 (the 60 does not make use of software generated envelopes like the 106 for the VCAs) attributed to that voice is either not generating an envelope contour or is not receiving the correct ADSR levels.