To check which voice IC is bad, do this:

1. turn the synth on.

2. press "poly1" button.

3. press lowest key, then next to lowest, then next to next to lowest...etc. 
(include the black keys too!) the lowest key is voice 1, next is voice 2, 
the next is voice 3.....etc. When you press a key that sounds "funny", it is 
associated with the bad voice. (you only have to press the 6 lowest keys)

4. to double check, repeat steps 2 and 3 above.


note: you may wish to manually dial up sounds with only the square wave,
or only the saw wave, or only the sub Osc wave to verify which IC's have
problems. Sometimes only one waveform will fail on a voice IC. Be sure to
rule out the possibility of a failed filter IC too!

Also don't be surprised if you find problems on both voices 1&2 or 3&4 or 
5&6.... the reason being: there are only 3 voice IC's in a Juno-106 
(two voices per IC) Sometimes the IC fails and takes out both voices.

The voice IC is a SIM-like-mini-circuit with black epoxy coating over it.

another note: The Voice IC SIM's go from right to left as you open the
synth and look in:
___________________________________________
|                                          /
|                                          \
|   V6&5       V4&3       V2&1             /
| F6    F5   F4    F3   F2    F1           \ 
___________________________________________/

on each side of the Voice SIMs are similar filter SIM's (1 per voice).
They are smaller. I have seen only 2 fail and about 12 voice IC's fail.

Warning: Roland circuit boards after 1982 (such as those in the Juno-106) 
have plated through holes. This makes IC removal very tricky even with a good
de-soldering workstation (The legs are held by solder on the top, bottom
and inside of the hole). It is very easy to damage a solder pad or rip
up a trace!!! If you are certain which voice IC is bad, carefully cut it
from its legs then remove each leg individually (heat the leg on the
solder side then pull the leg through from the component side using 
needle-nose pliers).


One more thing... surrounding each Voice IC is a cluster of trimmer
pots. It is here where you can adjust the filter resonance, cutoff freq.,
volume...etc. for each voice. It is possible (but unlikely) that someone
could have turned the cutoff trimmer or VCA trimmer down on one voice.
Thus causing apparent loss of a voice.

I'll soon write a simple procedure where you can increase the cutoff
and resonance of a 106 by just adjusting the trimmer pots and using 
your ears to balance all voices. (the most accurate way to calibrate 
certain parts of a synth in most circumstances)

From your friendly lab tech Philip