Micromoog basket case

[armillary]

Can you have any kind of attack and decay time before the sustain stage is reached (when powering up the synth with attack level to maximum)?

If not, is switch 601 (contour bypass) in the "ON" position ?

If not, then it could be IC601 (3080) that is maybe stuck open... ?

Or R606 trimpot (VCA balance) that maybe needs recalibration ?

The 556 Timer has been replaced.

Turning it on with the long attack did nothing but normal pitch wailing/stabilizing.

The Filter contour works, and the loudness contour works, but only when triggered by S&H Auto and with bypass 'Off". S&H Auto is incidentally the only Mod Source or Route that works, and the contours the only dest? The Source rotary switch might need replacing as it is gummed up from excessive oil/lubing. Is it possible the Keyboard voltage isnt making it thru the Source switch? Block diagram shows Keyboard feeding first into the Source knob?...

Currently the pitch ribbon is unplugged and the mod wheel is non functional... Dont know what this adds up to...

[thealien666]

There seems to be several issues remaining with this synth. And remotely trying to diagnose them all, with only the help of schematics and not having the instrument in front of me, makes it rather difficult to do. I'm afraid I can't be of much more help... Sorry.

Best of luck to you.

P.S. One final suggestion: cleaning all switches and pots and insuring that they're working properly (electrically and mechanically), first and foremost, and making sure everything is connected as it should will eliminate a source of puzzling behavior, and ease the pinpointing of real problems remaining on the boards.

[armillary]

Thank you for the advice and suggestions offered. I'm sure I will work through these remaining issues over time. It's certainly come a long way back from where it was in January. As was said, some things can't be fixed online.

No questions today, just offering some amusement. The Octave and Source rotary switches have this dried yellow goo on them, I assumed it was grease, sloppily applied many years ago.

http://home.comcast.net/~armillary/Micr ... CN4242.JPG

What's interesting about this goo is it's hard like plastic, and contact cleaner, flux remover and even carburetor cleaner (on a q-tip of course) don't dissolve it. Hopefully alcohol or paint thinner will.

[thealien666]

Wow! I didn't realize in how bad a shape this thing was...

Was it stored in a scrap yard ?

That yellow stuff might have been some kind of sealant ? The best thing could be to simply desolder and replace those 6 positions rotary switches with new ones (not expensive)?

[armillary]

Well yes, I heard it was stored outside, under a tarp, next to several Hammond B-3 organs, also under tarps, in rural Virginia. No kidding. At least that's the way my son described it. He picked it up. And there was a Micromoog on ebay recently which was rescued from being stored in water for a long time. This one is far better than that. But I didn't call it a basket case for nothing.

[armillary]

I've seen those 2P6T switches. If they'd fit I'd buy some in a minute. I just don't know if they'd fit yet. I guess I'd better buy one and find out.

[armillary]

My theory is that Bootsy Collins left this one in DC some time in the late '70s. It's got gold glitter on it. It's been rode hard and put away wet.

[armillary]

Just ordered one to try. Exactly what you pictured. It's worth a shot.

Which reminds me that ebay seller u-barn still has MOTOROLA MC1468L power regulator chips for the Micromoog for $4.90 each. One got mine working again. They're very hard to find.

[armillary]

Here's an update on the Micromoog basket case. Several problems were resolved with one stupid-simple fix. The output from the mod wheel goes through the "normally closed" contact of the external mod source jack on the back of the chassis. The normally closed contact had become "normally open", so nothing was returning from the mod wheel to the main board. Which made the Source rotary switch seem like it wasn't working. For now I have wedged something in the jack to keep the contact closed. Now the mod wheel works and the Source switch works, and the basket case makes lots of new sounds. Several trim pots have been replaced thanks to Kevin's advice on which Bourns models to use. The biggest remaining problem is the keyboard trigger voltage which remains stuck on. For a test, I replaced IC202 with a 1458 with pin 7 removed, and used the S-trig in to trigger the contour generator, and that works. That's all for now.

[thealien666]

Full recovery is always made up of a lot of small, but significant, improvements. Keep at it !

[armillary]

And another breakthrough on the basket case. Never underestimate the value of flux remover! This afternoon I went over a number of the chip sockets I'd installed and cleaned up the solder joints with flux remover and q-tips. When I originally soldered them in a couple weeks ago, I checked them with a loupe and thought they looked really good. Apparently not good enough though. I tested the Micromoog to see if there was any improvement, and found the keyboard trigger is working normally now. When you release a key, the key stops. So now I've tuned the oscillator, the filter, the VCA balance and the trill trim. Next on the list is the ribbon controller, which is missing the ribbon.

[3391]

A great read ! I've just finished repairing a MicroMoog that had most of it's semiconductors zapped by a pulse of high voltage , I know not where from . Not a single one of it's 'blocks' worked when I received it , but the crowning glory of it's fault list was the fact that a short section of track connecting two large sections of groundplane had been neatly vaporised .

This separated the ground reference into two ground references , one of which floated in relation to the other . These two references were distributed randomly around the circuit blocks because of the way the groundplane is laid out . The effect this has on the operation of the circuit are many , various , and utterly baffling unless you've designed PCBs .

Knowing that the groundplane is actually two groundplanres is one thing , finding the break on that PCB is another thing entirely . And that was just the start !

Excellent to hear you got that one going . A fine demonstration of the fact that persistence is EVERYTHING when repairing old synths like this .

[Kevin Lightner]

Just thinking out loud:

The knobs used on Micros and Multis have a piece of steel inside that rusts easily.
When they rust, it's just as if someone superglued the knobs on.
They stay on that tightly!

So maybe... someone pries the knobs off and breaks some of the shafts (especially on the selector switches.)
What you might be seeing now may be some glue that was used to fix shafts that broke when the knobs were pried off.
Nothing to do with the Moog originally.

Just a guess.

K

[armillary]

Thanks Kevin, and welcome 3391.

In the end, the goo on the rotary selector switches (seen in the photo) turned out not to be a problem. Once I fixed the nc contact on the mod jack, and the mod wheel CV could return to the main board, the mod and routing problems disappeared. Fortunately the switches were in good shape. I think the goo dripped on the board from somewhere else.

This main board had two bad traces. One was a 15 volt trace right at the OSC Scale trim pot and was repaired previously. The other was from pin 1 of IC304, the summer CA3046. The break in the trace was so small and precise looking I've wondered whether it might have been a production mod. Anyway, I resoldered them both.

The Micro is working great, and has a CP-251 and a Electro-Harmonix 8 Step Program now. Check out that 8 Step, it's a very cool CV sequencer and a bargain too.

Here's a question I've been meaning to ask. My son says his Micromoog gets out of tune when the humidity in his apartment gets too high (like 65% rh) although the temperature is 78 F. Anyone heard that one before?

[thealien666]

The Micro is working great, and has a CP-251 and a Electro-Harmonix 8 Step Program now. Check out that 8 Step, it's a very cool CV sequencer and a bargain too.

Question: where do you take the trigger or gate signal from ? The EHX doesn't generate any (AFAIK) ?