JUNO-106 Test Mode Question

Synth Repair
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Greetings, everybody…first post. I recently acquired a free JUNO-106 in need of a lot of love. While I’m pretty new to synths, save for refurbishing and repairing my brother’s MicroMoog some years ago, I’m not new to electronics troubleshooting and repair, so the JUNO is in the midst of a full spa treatment.

After verifying correct power supply function I did a high-level function test just to verify basic operation, like that systems appropriately powered up and I could make it make some kind of appropriate noise. That revealed basic functionality was a “yes”, but a substantial number of the tactile switches were non-functional, including the POLY 1 & 2 switches, which prevented me from testing the voice modules. So my focus so far has been on a full rebuild of the Panel Board (all new tactile switches and slide potentiometers, disassembly and full servicing of the HPF slide switch, new dust shields and new electrolytic capacitors, as well as a thorough cleaning). I also cleaned up the Jack Board and MIDI board as well as the top panel, put that all temporarily back together to then test the voice modules. My question is regarding the Test Mode.

I made a short YouTube video about my question which is here: https://youtu.be/jL2zlkSp23k?si=kRF0L2_2Lk58iLdo. Basically I’m a little confused because the Service Notes indicate the PATCH buttons are non-functional in the Test Mode, but when I power up in the Test Mode, and then engage the POLY 1 & 2 functions to serially test the voice modules, if I do nothing other than that, there is no sound. This initially led me to believe all my voice modules were dead, which was confusing because when the JUNO is powered up in its normal state, it seems to work (I can pull up patches from every group of both banks and they make what I consider to be normal/expected great sounds). So then today I thought to try pressing any of the PATCH buttons after engaging the POLY 1 & 2 functions to see if that made any difference, and indeed it does…again, check out the video if you want to see and hear what I’m talking about. But I’d just appreciate any feedback confirming what’s happening is normal as far as what I’m having to do to perform the voice module testing (and some confirmation my voice modules are good), and otherwise if it’s not normal and any suggestions. I have a couple other videos of the project so far too in case that’s of any general interest.

Thanks!

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Hi, Not sure specifically about your question, but IMO the best test for working voices is to scope TP4. This constitues 6 header pins on the voice board. In the basic test mode (see below) the synth will cycle through the voices and the resultant waveforms are observable on the pins of TP4 - one pin per voice. It’s a good starting point.

Key assignment modes (after entering standard test mode)

  • Mono Mode:

    Select with the Arpeggiator switch in the UP position. All six voices are assigned to the last key pressed, creating a fatter, monophonic sound.

  • Rotary Mode:

    Select with the Arpeggiator switch in the UP/DOWN position. Voices are assigned in a rotating order (voice 1, voice 2, etc.). If you hold four keys and release three, the next key will be assigned to the next available voice in the sequence.

  • Non-Rotary Mode:

    Select with the Arpeggiator switch in the DOWN position. Similar to Rotary Mode, but if you hold four keys and release three, the next key will be assigned to the first available voice (voice 1).

Exiting test modes

  • To exit and return to normal operation, turn the power off for at least three seconds, then turn it back on normally.
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Thank you so much for the reply and I am so sorry for not updating sooner…after further research as well as study of the Service Notes (and some trial and error with my test kit), AND some specific and current guidance here in this forum, I was able to make my way through the full calibration procedure set. Your reply is a good reference point and hopefully also helpful to future readers. Thank you.

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