Juno 106 voice chip repair questions

Hi, new here and just started working on repairing a Juno106 I got that was not working properly. It was making lots of crazy noises and crackling, sounding all the time, etc. I decided to try the acetone fix to strip the resin off the chips and then socket them back into the board.

Unfortunately, after all of that I no longer am getting any sound at all from most of the chips and in some cases just a very very quiet tone.

Trying to troubleshoot my first concern is when I check for continuity on the pins of all of my sockets I am reading pins 4,5,6,7,8 as all showing continuity (assuming pin one is the one that is on its own). This seems wrong to me as if I’m reading the schematic correctly 4&5 are positive and negative voltage and 7/8 are ground (so those should be common).

I can’t see any obvious shorts in my soldering so I’m wondering first can anyone confirm that these 5 pins should not show continuity? I would think they should be separate.

And second, any other obvious places to look for a cause of a short? All of the sockets are showing the same continuity so is there a common component or IC that could be causing the problem? I don’t see any obviously compromised components or cut traces.

Thanks in advance,

Hey, welcome to the forum!

Those pins should definitely not have continuity. Are you testing continuity with the ICs out of the sockets?

If they are continuous with no IC then I would suspect the solder might be bridging beneath your sockets, especially if they are all continuous to each other (ie pin 4 is continuous to 5, 6, 7, 8). You may need to desolder one of the sockets and check if there is still a short.

Bad electrolytic capacitors could also lead to shorts between some of these pins, it’s usually worth it to replace all of those when you’re working on anything 20+ years old. If you haven’t worked on the power supply yet it may be worth it to take a step back from other troubleshooting and make sure it is functioning properly when disconnected from the rest of the synth, the shorts could be on that board.

You can do more continuity testing with boards disconnected from each other to find which board the short is on. Disconnect the power supply and see if those pins on the sockets are still shorted.

Hi! Thanks for the quick reply. Let me give a little more info…

  • I’m testing the board disconnected from all the other boards including the power supply.

  • I’ve desoldered 2 of the 6 sockets and still showing continuity across all of those 5 pins. If they’re not supposed to have continuity then I’m assuming they must all be common which is why they all show the same pattern? In other words ground is common, +v is common, etc. pin 6 is vcf control so that is probably common too - it would be shared by all the voices I think. Sounds like I should desolder the other sockets next I guess? I honestly don’t see any obvious bridging but I guess it’s possible it’s under the socket on the top of the board where I can’t see it.

  • as far as caps are concerned I haven’t replaced any of those but there are lots of them. I guess I wasn’t thinking it would help due to the fact that I’m shorting across all those pins. Seemed more likely an ic I guess but I don’t know how to go about finding which one.

Thanks again, please keep the suggestions coming! If anyone has a 106 and can do a quick continuity test on their module board I would be so grateful. Just to make sure I’m not crazy.

I think I may have misunderstood the original question. Do you mean for example pin 4 of socket 1 is continuous to pin 4 of socket 2, pin 4 of socket 3, etc? That would be normal but first I thought you meant pin 4 is continuous to pins 5, 6 ,7 and 8 for each socket. That would not be normal and just one of the sockets being bridged with solder could cause them all to appear shorted like that.

Pins 4, 5, 7 and 8 should all be common between sockets however for each voice pin 6 gets its own control voltage from IC23 and the opamps that follow. If all of your pin 6’s are shorted together then IC23 could be the problem.

No, you understood correctly - within a single socket I’m seeing 4,5,6,7,8 all continuous. So definitely an issue. I’ll start by desoldering the other sockets I think to see if that helps.

Hey guys, quick update this morning… I tried measuring the voltage on the board where voice chips go, and it looks like there is no short - I am getting -15v on pin 5 and +15v on pin 4, as expected. So I’m guessing the continuity is due to components that have low resistance when the circuit is off?

So that makes me think that the next logical step would be to see if a new voice chip behaves better - if not then there must be some other problems with ic’s or components on the board which I will definitely need a tech to help find. Ordered a new one from here to test with.

Does that sound right?

Thanks again,