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Moog Opus 3 Multivibrator needs a kick start to start

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  • #16
    Hmmm. That's interesting. I just measured it and it takes almost a full mS to get to 6 volts. This is after a full recap. So I don't think its the reservoir cap, BUT I did replace the tantalum bypass caps for the regulators (C70-C73) with electrolytic's for some unknown reason. Maybe those bad boys are slowing the DC down too much and I need to get tantalum's back in there? I also bumped the reservoir cap up to 63V, but I wouldn't think that would make that much of a difference.

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    • #17
      Did the fault exist before the re-cap?
      Originally posted by Enzo
      I have a sign in my shop that says, "Never think up reasons not to check something."


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      • #18
        Sort of. It did, but he could power cycle a couple times and it would turn on. Now I can not get it to turn on with out "jumping" it. I was a bit silly to recap without figuring out the issue first, but I was hoping the recap would fix it.

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        • #19
          Ah if only hope could replace troubleshooting...
          Education is what you're left with after you have forgotten what you have learned.

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          • #20
            I know, I know. It wasn't my finest moment.

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            • #21
              So Ive tried getting the speed of the power supply down to 100uS but the fastest I can get it is around 700uS. I tried replacing the tantalums with low esr, the filter cap with low esr. Replaced the regulators. Bypassed the power switch. Im starting to run out of ideas.

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              • #22
                If supply rise time is critical, C56 the decoupler at U15 is worth a try (if you haven't already replaced it).
                edit: sorry, I see the bypass cap was already covered in posts # 9 & 11
                Last edited by g1; 09-02-2022, 03:59 PM.
                Originally posted by Enzo
                I have a sign in my shop that says, "Never think up reasons not to check something."


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                • #23
                  No other ideas unfortunately. Not trying to 'offload' you but there may be people more familiar with this unit at the moogmusic forum. There have been some specific opus 3 repair threads in the 'moog music general topics' section and there are some techs that are specializing in vintage moogs. It might be worth a try.
                  Originally posted by Enzo
                  I have a sign in my shop that says, "Never think up reasons not to check something."


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