'IF' your JUNO-106 has (a) broken VCF/VCA chip(s) or WAVE-GENERATOR chip(s), then this simple test procedure will show you which one(s) it is/are. Other problems with the circuitry around these chips is also possible, but in 95% of all cases, it will be one of them that causes the problems.
This test is by no means final. Only an experienced synthesizer technician can perform the necessary tests to check what the exact problem is with you JUNO-106.
Some tips for servicing can be read here.
If you see any errors or have an comments: please contact me on: , but do not ask me for synthesizer repair lessons. I simply do not have the time for that.

-Hold KEY TRANSPOSE, turn on your JUNO-106 and release KEY TRANSPOSE.
*The display should now show '-_'. This means that your JUNO-106 is now in
 'test mode'.
-Turn on POLY 1 and POLY 2.
*Your JUNO-106 is now in 'rotary' mode. The display shows which voice is
-Do following settings:
	-RANGE to '8
	-PWM: man
	-SQR & SAW: off
	-VCA switch to ENV
	-All sliders to 0 except:
		-VCF FREQ: 10
		-KYBD: 10
		-VCA: +5
		-D: 10
		-S: 5
		-R: 2,5
*Your JUNO-106 should now be silent

-Set NOISE to 10.
-Play a few notes.
*You should hear noise (and noise only) from all voices.
*If you hear constant noise without playing a key, then you have one or more
 hanging VCA's.
*If you hear no noise at all, then you have a dead noise generator. There is
 only one noise generator.
*If you have one or more voices without noise, then the VCA for that voice is
-Set NOISE back to 0.

-Turn on SQUARE.
-Play a few notes while playing with the PWM slider.
*You should hear  sound from all voices and pwm should work too.
-Turn off SQUARE and turn on SAW.
-Play a few notes.
*You should hear sound from all voices.
-Turn off SAW and set SUB to 10:
-Play a few notes.
*You should hear sound from all voices.
*If any of the above failed for a voice (except the ones that already failed in
 the above noise test), then that voice has a broken wave generator chip. 
*If you have a hanging note, then play some different notes with any wave form.
 When the pitch of the hanging note changes, then the voice you last played has
 a broken VCA.
-Set SUB back to 0.

-Make sure SQUARE, SAW, SUB and NOISE are off.
-Set FREQ to 5.
-Set RES to 10.
-Play a few notes.
*You should hear sound from all voices.
*When playing 6 times the same note, you should hear 6 time 'almost' the same
*If you hear no sound from a voice or the pitch is 'way' off, then that voice 
 has a broken VCF. If the pitch is a little off, then your JUNO-106 needs
-Now play a bit with different RES settings. The sound should disappear for all
 voices at about the same RES level. If a voice still plays with a RES level far
 below the ones where the other voices stop, it means that this voice's feedback
 VCA is hanging.
-WAVE-GENERATOR chips are the MC5534A IC. There are 3 in your JUNO-106. VOICE
 1&2, 3&4 and 5&6 each share one. Except for the really old ones: These have 2
 chips glued together, but these 2 can also be replace by a MC5534A. They are
 still available from ROLAND.
-VCF and VCA are in one combo chip: the A1QH80017A IC or the A1QH800170 IC for
 the really old ones. Identified by 80017A or 800170 stamp on the chip. These are
 really crap chips and are no longer available. There are 6 of them in your
 JUNO-106. One for each voice. Replace them with my D80017 modules. They sound
 exactly the same and are a lot more reliable than the original ones.