Vintage Synth Repair

Hi,

Any been here and can give me a clue before I dive in a Juno 106?

Playing a key at a time, after the 5th key played, the 6th does not play. Starting to play again after the key that did not play again the same sequence happens: 1 to 5 ok 6th =no play. No matter what keys are played i.e. not in order, up or down etc.. each time the 6th does not play.
Another symptom that could/or not have to do with the above symptom is that a C note is heard in the background as soon as synth is switched on. I also noted (though I’m not sure yet) that this note in the background changes to the last 5th key note played after which the 6th does not play.

Any help please?
Btw.. the A1QH800170 chips are all original (coated/covered, in - epoxy?)

Thanks guys,
Noel

Sounds like the typical chip problem.

Run the following test: Power up the Juno while you hold the "Transpose"
button down. The press bothe "Poly1" and "Poly2" at the same time so both
lights are up. Press "Bank 2" and then press any note six times. The active
voice is displayed in the readout. You'll see which voice is dead.

Thanks Malte.. will check this out in the morning 
- - -

  
Sounds like the typical chip problem.

Run the following test: Power up the Juno while you hold the "Transpose"
button down. The press bothe "Poly1" and "Poly2" at the same time so both
lights are up. Press "Bank 2" and then press any note six times. The active
voice is displayed in the readout. You'll see which voice is dead.

Ok.. put IC13 & IC11 in acetone for about 1 week
13 could be done but 11 was stubborn so I replaced the solution
and put back in for 1 or 2 days then ok.

I then noted the container I used was not really air-tight and could be
the acetone solution deteriorated as when I replaced it with fresh one
I got good result with the second IC. Now I got voice 1 & 2 back, good.

However now I have a hanging note faded in the background as soon as synth switched on
(as originally as before besides voice 1 & 2).
Do I have to deal with all these ICs or I could use Test mode to pin point the faulty one?
Thanks for help!
Noel

From: Malte Rogacki 
Sent: Thursday, May 23, 2013 10:30 PM
To: vintagesynthrepair@yahoogroups.com 
Subject: Re: [vintagesynthrepair] Roland Juno 106S - note stealing ??

  
Sounds like the typical chip problem.

Run the following test: Power up the Juno while you hold the "Transpose"
button down. The press bothe "Poly1" and "Poly2" at the same time so both
lights are up. Press "Bank 2" and then press any note six times. The active
voice is displayed in the readout. You'll see which voice is dead.

I would say clean all the chips. If there is still leak thru, post again. I found 100-200k or so resistors on the vca input to the chips (to gnd or pwr, i don't remember, don't have my 106 anymore), largest selected to just cut off the sound, worked pretty well. I will hunt down the schematics and give more detailed guidance if need be. I suppose one might try the fix without cleaning, I don't know....
Hugh