MiniMoog Osc 1 & 2 dead :-(

[JohnLRice]

OK, I've put this off for a long time and for some reason tonight I decided to open up my Minimoog to fix it (instead of finishing my DIY power supply )

Long story short, at one point I was rearranging things in my crowded studio and the MiniMoog was standing up on end temporarily while I was moving other stuff and I bumped into it and it fell over and landed flat on the floor. (yes, ample swearing ensued)

Before it fell over all three oscillators worked fine, now only #3 works. I feared cracked circuit traces but I hoped for something simpler. Either way, I've fixed cracked traces before so I thought I could patch it up but, I can't seem to find any! I spent an hour with a bright light and a magnifying glass but nothing obvious. The edge connectors had a little green oxidation on them so I cleaned them with a little Caig Pro-Gold but, of course that didn't fix anything.

Any pointers? Tomorrow when I'm rested I'll try to test if the oscillators are actually working on the board but something down stream is bad (like a switch or wire etc)

Thanks!

Here are some pics for fun:

[Kevin Lightner]

Sorry for your misfortune.
I could provide tons of pointers, but have confidence in your abilities also.

If it was mine, I'd get rid of the transistor array sockets and check the crimps of the edge card flags.
I'd also throw the Caig stuff in the trash and clean up the edge connectors.
If there was green, it's probably copper oxide and the Caig will more likely move it around and trap dust than it will help the connections make better contact.

If you find no audio downstream, consider moving the board around or the wires and connector flags while listening.
The flags are only crimped onto the wires and the presence of oxidation won't help there.

I think you'll locate the problem given another round of troubleshooting.
But if you need any parts you can't find around, let me know.
Good luck.

[JohnLRice]

Thanks much for the tips, Kevin! I'll give it a go!

[EricK]

Oh John, Id probably have about 4 strokes if I toppled my MiniMoog.

Talk about the Colossus of Rhodes!


Eric

[mayidunk]

Four strokes and a heart attack!!!

On another note, I'm looking at the circuit boards, noticing those electrolytic capacitors, and wondering how much more life they might have after 30 years. Is there a point where one would start considering replacing these before they start leaking? Maybe Kevin could chime in on this.

John, I hope you find an easy solution.

Bob

[enatrn]

Any pointers? Tomorrow when I'm rested I'll try to test if the oscillators are actually working on the board but something down stream is bad (like a switch or wire etc)

Sad story, sorry to hear that. I'm afraid it could be anything, and the full-blown oscillator work is the only solution.

[acorkos]

check the wiring at the mixer switches

[Electrong]

Let us know who's right when you find out, please.. I know who I'd bet is correct, but obviously it could be a few things.

[Subtronik]

I hope you can fix it yourself, good luck.

[Kevin Lightner]

I replace every electrolytic on every vintage synth that comes here.
But on that VCO board, there's only one, a 2.2uf.
The others are solid tantalums.
So far, I've only seen one of those ever go bad in a Moog.
Not the same type of tantalums that often go bad in Arps.
They're also very expensive for a capacitor, so I don't stock them.
No use having pricey caps age in a parts drawer either.

Regardless, I doubt this is the problem with John's.
I expect he'll come back here and say it was something physical that broke connection and not a bad component.

Never know, of course.
I just have confidence he'll find it.

[mayidunk]

My mistake, I thought those cans were ECs.

I also wasn't thinking that the problem was leaking capacitors, just curious as I've heard some say that some ECs leak because they're lower quality, and others just last and last. However, ECs just lasting that long doesn't sound right to me, especially as they don't need to leak to start going south. I figured that Moog may have used higher quality ECs in their designs, especially in the modulars more so than the Mini, so I thought I'd ask.

[Electrong]

There's an "update" that involves the wires getting soldered to the flags, I think. There may be a reason why. If you jolt the synth then all those connections which are physically attached stand a chance of coming undone. Think loose solder joints only without the solder..

[Kevin Lightner]

There's an "update" that involves the wires getting soldered to the flags, I think. There may be a reason why. If you jolt the synth then all those connections which are physically attached stand a chance of coming undone. Think loose solder joints only without the solder..

If they're oxidized, they'll be hard to solder, if possible at all.
I have replacement flag pins and even the whole wiring harnesses in NOS condition from the last run of Minis Moog made.
Cool thing on those are that the much later ones have gold-plated flags where needed most.
Even the Cinch connectors are gold-plated on the later ones.

So you're right, but it might be too late for his.
Might have to cut them off and start over or replace the whole harness, connector, flags and all.

[JohnLRice]

Super quick because I'm almost asleep . . .

First, thank you all for your kind works of support and ideas to try! I really appreciate it!

I'm starting to zero in on the problem but I really have no idea yet why it is doing or not doing what it does.

I've found I CAN get some sound out of OSC #1! But . . . I have to give it a high enough voltage! (play high enough on the keyboard) But one I have output, I can change Osc #1's range knob and get lower notes, so long as I don't go too low on the keyboard (I haven't tried with external VC yet) Plus, weirder yet, the range switch for Osc #2 has to be in the highest couple positions for this to work! I can get no sound out of Osc #2 but the routing is OK (I can hear the noisy level and waveform knobs if I move them)

I've looked and looked and I haven't found anything shorting around the range switches and they 'feel' OK (I'm assuming nothing is broken inside)

Could it be a weak transistor(s) some where? A bad cap?

Uuuhhmm, I just remembered I forgot a basic rule of trouble shooting . . .check the power supply voltages first! I'll do that tomorrow . . . .

Thanks again everyone!

[thewaag]

Sorry to hear about your accident. I just have one question....

MY GOD MAN! WHY DO YOU HAVE A MINIMOOG JUST LAYING AROUND ON IT'S END IN YOUR STUDIO??

Mine is sitting on the top rack of a stand, with a halo of lights around it to illuminate it. Mounted on this halo is a set of the new Dyson bladeless fans that are on 24/7 in order to keep any dust from settling on it. There is a box of latex gloves sitting next to it so that you can put gloves on before you touch any surface of it. There are motion sensors on the light halo that register when you approach the Mini. When you get 3 inches away from the power switch the pre recorded sound of a choir of angels make an "AHHHHH" sound.

Of course I am only kidding (slightly) but a Mini should have a proud place in your studio, and not be left up leaning on your wall.

I am not really busting your chops, although it might seem like it. I just couldn't let this one slide by without chastising you just a bit.

Hope you get it up and working soon.