Tuesday, May 1, 2012

Juno-60 service

Still acting weird? Ground problems!

Just when I thought I had fixed all the problems with the Juno-60, I noticed it started jumping into manual mode and acting weird again when I was mocing the sliders.
Now what?!


I put the Juno-60 on the workbench and tested it for a while.
As I expected the sliders to be causing the problem I kept wiggling them, pushing the front panel to check if there were any faulty connections somewhere causing this.
I put the Juno-60 back in the rack and tested it. Seemed to work fine. Odd...
Then a couple of days later when I tried it again, the same problem appeared! Argh!!!

Luckily, I found some information in the Juno 60 service notes,  p 19.


"Because of the AC ground, a "ground loop" may be created when the DCB cable is connected between the Juno-60 and its party (equipment). As a result, a certain-level digital noise may occur. In the later Juno-60 the noise is considerably reduced by rearrangement of ground paths together with installation of Panel Board B improved version, 052H411C (pattern relayout).
The modification is conducted at the factory on the units with serial numbers 253800 and subsequent.
For the units prior to SN253800, alternative modification can be made for the purpose of noise reduction."

Well well! Guess if my Juno has an older Panel Board B and lower SN than 253800.
Also, since I don't connect anything to the DCB jack when the Juno was on the workbench I never saw the problem there. Annoying!

Fixing it

There's a picture in the service manual describing the modification.
I didn't really analyze it that much but I guess it separates the ground into two areas on the panel board instead of letting everything share the same ground.
This is done by cutting a trace and soldering a wire at the cut, while the other end of the wire should be soldered to ground on the PSU board.

Here's what it looks like in my Juno-60 after I did it.

Black ground wire ends marked with dashed yellow circles.

Here are close-ups of the two wire ends.
Anode of D2 on PSU board.

Trace cut and wire soldered to pin marked 81 on Panel Board B.

I haven't had any problems with it since then!
Wooohoooo! :)

Also, I replaced the two broken 3-way switches for the arpeggio mode and range selectors.
So finally, I can play with the arpeggiator :D


  1. Badass fixin :D

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  3. Weren't you suppose to solder 2 wires like it said in the service doc?
    Did it it really work?
    If so i will do as your pic shows although my panel board B seem to be a bit different than yours.


    1. Two? It's only one (page 19), though it's drawn as a really thick wire, which I assume is the insulation. It only attaches at one point (GND in the PSU) and at the top half of the split trace on the panel board, so there shouldn't be anything else to do.
      Do you know of another modification?

      Regarding your different board, please note the manual says:
      "The modification is conducted at the factory on the units with serial numbers 253800 and subsequent."
      and then
      "Note: This modification has no effect on later units."
      So check the serial nr on your Juno so you're not doing an unnecessary mod.

      I have to say, my Juno-60 is still resetting at times :( Though not as frequently as it used to...

  4. Just did this modification exactly as you did. Except my board looks slightly different. My JU-60's sn number is 3191, so I deemed it necessary to mod it last night with my friends. We followed the service manual and interpreted figure 19 to be one thick wire as did you. Soldered it to the exact same point you did to the PSU and to 81 on Panel Board B. However the board I have looks different than yours and the one found in the service manual. Please see my post found on this forum, that has pictures of my modification. http://www.vintagesynth.com/forum/viewtopic.php?f=5&t=69803&p=714164#p714164

    If you have figured out the problem yet, please let me know, I have a show in two weeks that needs my Juno to run correctly.

  5. This saved me so much money and time!
    My Juno is up and running perfectly again!
    Thank you Synthpeter.

    Mathias from Denmark

  6. I think the problem on new or old versions can be the connection at 57 on the bottom board. I do not know what it is called but it is where several connections are. When you pull it off, the sound goes dead. Anyway, I cleaned that connection really well and the problem is gone with patches jumping into manual mode.