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  • Has anyone noticed a accumulation of yellowish tint in the acetone baths or for that matter on the boards ? I got to thinking that the whole issue may be solder flux related and that the board may have been underclenaed. As flux ages it can and often does pickup moisture and can cuase havoc in a very low current circut.

    also I would stay away from varnish coatings as many of the spray on coating can and do often become hydroscopic over time. Silicone conformal is the best way to go as it is 100% non conductive.

    Comment


    • the trace situation is repairable. the issue with the sand resistor is entirely different. If you knew roughly what the range of impedance was there you could build a high precision trimable circut with a potentiometer and trim it into compliane but without a base resistance thats a futile effort.


      .

      At any rate once I finally freed the chip and gave it a bath in acetone, the epoxy layer came off very easily even after only soaking for about 20 hours. The corner that broke off has several traces and the split goes through one of the printed resistors. (I'm still kicking myself by the way...)



      So my question to the experts is, am I totally screwed, or is there some chance I can repair the traces (super glue and conductive pen perhaps?), or is it time to order up a clone / replacement chip and learn to use an oscilloscope? Speaking of which, has anyone every used one of these cheap usb / software scopes that I see on ebay? Do they actually work?

      Thanks for any help!!

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      • Yes, I did notice that there was a fair amount of flux left on the board, I washed it all off of mine with Serious Flux Remover that can't be bought anymore. And I'm almost out of it. Drat.

        As for patience: Yes, you'll need it. After the first day or so, the coating should have softened enough that you can cut off the edges for the coating from around the chip, exposing the edges of the ceramic. Then drop 'em back in and let them soak some more; This should let the acetone soak in better.
        Hurrr. Derp, derp, derp.

        Comment


        • Yes, I did notice that there was a fair amount of flux left on the board, I washed it all off of mine with Serious Flux Remover that can't be bought anymore. And I'm almost out of it. Drat.

          As for patience: Yes, you'll need it. After the first day or so, the coating should have softened enough that you can cut off the edges for the coating from around the chip, exposing the edges of the ceramic. Then drop 'em back in and let them soak some more; This should let the acetone soak in better.


          I'd bet this whole issue is solder flux the more I sit and think about it. I don't even have it Juno but this thread cuaght my interest. I'd bet the flux is getting conductive due to moisture wicking. I have had similar issues with automotive ECU's over the years.

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          • If so, why does it only seem to affect those chips in particular? Not disagreeing, but it seems a very "targeted" effect if that's true. Seems like it should be affecting other aspects of the synth, too.
            Hurrr. Derp, derp, derp.

            Comment


            • If so, why does it only seem to affect those chips in particular? Not disagreeing, but it seems a very "targeted" effect if that's true. Seems like it should be affecting other aspects of the synth, too.



              Could be a vendor issue. Maybe they used a insufficnet cleaning process. different vendors maye have supplied a whole slew of compnents.

              It there are other potted chips on the board maybe opening a few of those chips may shed some light on the subject.

              It could also be a problem specific to one plant and on manufacturing line. One line may have had a in adequately performing cleaning machine and the problem didn;t start appearing till many many years after the machine was out of production.

              moisture buildup in fluix takes time so no doubt that we might never see it unless the sealing agent fialed.

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              • Update: I finally got most of the resin off the chip this morning (aside from the back). In the process I managed to loose another chip leg, but was able to fashion two new ones out of old clippings. I re-installed the chip this afternoon and have been playing it off an on all day with great success!

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                • Hi everyone. I want to avoid desoldering the voice chips but it seems that 2 of mine are messed up. One voice chip causes notes to sustain or hang but there is also this annoying scratchy sound - and notes that play randomly when nothing is being played.

                  Are these problems caused by the voice chips alone? Could the scratchy sound be a loose ground or something? Is it possible to scrape away the resin without removing the chips?

                  Here is a song I made by playing 2 chords over and over in diagnostic mode

                  http://z1.droplink.me/downloader/5df68e3b1h613e28bcc7217a782d434g/broken--%28.m4a

                  Comment


                  • Are these problems caused by the voice chips alone? Could the scratchy sound be a loose ground or something?

                    Very likely it's the VCF/VCA modules (whate everyone calls the "voice chips").

                    Is it possible to scrape away the resin without removing the chips?

                    There's no simple mechanical way of removing the resin that I'm aware of; The modules will have to be removed so they can be soaked in solvent. If you're not comfortable doing this, then you should find someone who is.
                    Hurrr. Derp, derp, derp.

                    Comment


                    • I have difficulties in removing the resin between the IC legs. Any suggestions?

                      I was thinking since the resin is also under the IC itself, then it might still somewhat short the IC legs, since after removing the resin between the legs it still touches the legs from behind (As far as I can se from photos). Any thoughts?

                      Somewhere (I think on YouTube) I read that one should remove the more sticky resin on the 10 laser trimmed resistors. As far as I can see ElectricPuppy didn't do this and still got the chips to work. Any comments on that?

                      Thanks for a lot of good info.

                      -----------------

                      As far getting the 80017A voice chip off the PCB:

                      I got the chip out pretty easily by using this? inexpensive tool: Velleman VTDESOL3U Vacuum Desoldering Pump With Heater 30W.

                      I vacuumed each pin 2 or 3 times from the back of the PCB - only heating each pin a few seconds every time. I then used a small screwdriver to wiggle? the pins gently about to loosen them (still from the back of the PCB).

                      After that I very, very gently wiggled the chip itself until it practically fell out. I didn't use any force anywhere in this process, since that might damage the chip.

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                      • I removed the resin between the legs on the IC pins with a very fine pick and pair of tweezers. Very fine tweezers, actually. There was a lot of squinting involved.
                        Hurrr. Derp, derp, derp.

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                        • I gave up on removing the resin between the legs on the IC pins after 5 days in the acetone. But I just installed the chip (80017A 40A) and the damn thing works. Incredible. Just incredible.

                          How important is the silicone conformal coating procedure? What will happen if I don't do this?

                          Comment


                          • Honestly, I don't know. I did it to mine mainly as a precaution. I seem to recall reading somewhere that the exposed resistors are susceptible to moisture (i.e. humidity changes), so... Your mileage may vary.
                            Hurrr. Derp, derp, derp.

                            Comment


                            • I bought now MKS-30 + PG-200. Should I do this chip revival as soon as possible or is it wiser to wait until it starts the "acting weird"?

                              Is it really a long term solution to remove the epoxy and replace it with silicone?
                              "I'm totally opposed to all these expensive bull**************** computers (sequencers). They can do whatever you want but not in the time you want. People have lost the essence of time. One said to me: 'With this new computer I can create something in one or two minutes'. This is an eternity. I can do that in a split second. But the split second doesn't come into account because the previous computer could do it in 10 minutes - so for them, 10 minutes to two minutes is really great progress!" - Vangelis

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