JUNO-106 TEST PROCEDURE
'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: moc.ecnassianereugolana@ofni (Please enter this manually, copy-paste has been reversed to avoid spambots), but do not ask me for synthesizer repair lessons. I simply do not have the time for that.
#ENTERING TEST MODE & INITIAL SETTINGS -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 playing. -Do following settings: -RANGE to '8 -PWM: man -SQR & SAW: off -VCA switch to ENV -PORTAMENTO: off -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 #NOISE TEST: -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 dead. -Set NOISE back to 0. #WAVE FORM TEST: -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. -Repeat the above WAVE FORM TEST again with range set to '4 and then once more with range set to '16. *If you get different results for this test depending on the RANGE setting, then the multiplexer in front of the wave generator chip is broken. The wave generator itself might be fine. #FILTER TEST: -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 note. *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 adjustment. -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. #CONCLUSION: - 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 replaced by a MC5534A. - 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.
Copyright © Cask Strength Electronics 2021