Moog Opus 3 Multivibrator needs a kick start to start

[codystein9]

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.

[g1]

Did the fault exist before the re-cap?

[codystein9]

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.

[Enzo]

Ah if only hope could replace troubleshooting...

[codystein9]

I know, I know. It wasn't my finest moment.

[codystein9]

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.

[g1]

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

[g1]

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.