Faint output on Minimoog?

Jeebus · Post by **Jeebus** » Wed Mar 16, 2005 8:44 pm

My mini has stopped producing sound. If I turn the level up all the way I can hear it faintly, but it's extremely quiet. The volume contour section doensn't seem to work, at low settings it causes a thumping sound. Everything else works fine. The A-440 oscillator comes through loud and clear, which is strange considering everything else is so quiet..

Any ideas on how to fix it?

ebg31 · Post by **ebg31** » Wed Mar 16, 2005 11:51 pm

Have you tried changing the patch chord?

Perhaps, the output jacks need some cleaning, or replacing.

Jeebus · Post by **Jeebus** » Thu Mar 17, 2005 12:09 am

I've tried 4 different patch cords, that's not the problem, and the jack is ok. Remember that the A-440 tone works properly.

I'm guessing it's got something to do with the VCA's which reside on board 4, but I'm not sure how to isolate the problem.

HowIMadeMyMillions · Post by **HowIMadeMyMillions** » Thu Mar 17, 2005 1:07 am

Could be your mixer. Check the osc mixer switches. Check volume pots. Try your octave knobs as well....it could be they're stuck on lowlowlow. Have you tried your Osc3 too? Also did the unit work and then just all of a sudden stop? Check your output jack's connections as well. Just ideas....could be your VCA's but better look for the easiest/cheapest fixes first.

Jeebus · Post by **Jeebus** » Thu Mar 17, 2005 1:20 am

It was working fine, and then all of a sudden one day I turn it on and there's no output. Although the output is faint, I checked all other pots and switches, and everything works and sounds as it should, except for the loudness contour section. This leads me to believe that something is messed up in that section which is also responsible for the faint output.

gd · Post by gd » Thu Mar 17, 2005 2:19 am

I just went through the same thing with my Source, turned out that a screw was touching the board, once I put a little rubber cover over the end the sound was back.

Jeebus · Post by **Jeebus** » Thu Mar 17, 2005 2:56 am

Interesting... did it have that thumping sound as well?

I'm checking the screws now.

gd · Post by gd » Thu Mar 17, 2005 3:03 am

Jeebus · Post by **Jeebus** » Thu Mar 17, 2005 3:08 am

No screws touching... it must be a short somewhere else.

I appreciate the help, everyone. I hope I can figure this out.

MC · Post by MC » Thu Mar 17, 2005 2:17 pm

The rear panel VCA jack may be dirty. The Mini actually has two VCAs, a second one for modulation sources from the VCA jack. When nothing is plugged into it, it is "normalled" to a fixed voltage to keep this VCA wide open. If that normal connection is dirty, the VCA can be cut off. Try repeatedly inserting a plug into the VCA jack to get that dirt off.

Jeebus · Post by **Jeebus** » Fri Mar 18, 2005 4:07 pm

Interesting tip about the VCA jack. I tried inserting a plug back and forth to clean off the dirt, but that wasn't the problem.

This is a tough one.

Thanks for all the help so far guys.

Kevin Lightner · Post by **Kevin Lightner** » Fri Mar 18, 2005 10:01 pm

Here's a few checks.

Turn up the emphasis on the vcf. Do you hear the vcf self-oscillate?
If it does make noise with the vcf, do the orange keyboard tracking switches work (does it "play" the filter?)
Does the noise work?
Are the fuses ok?

Try this also.. as crazy as it sounds.... grab both sides of the mini rear chassis and gently flex it a bit around. The cards inside may have fingers that have missed their connections. Without opening it, you can simulate what a mini sees when it's transported. It may work again or make some noise. Don't go crazy and wrestle the beast to the floor, just jog it around a bit. Light taps and such. No hammers.

Also, *lightly* grab the small bundle of wires going into the keyboard area and move or lightly tug on them. If there's a bad cinch jones keyboard connector, CV won't pass, but the gate will. Normally the oscs will still sound though, they just won't change, if this is so.

Jeebus · Post by **Jeebus** » Fri Mar 18, 2005 10:14 pm

VCF self oscillates
both keyboard tracking switches work
noise works
fuses are ok

I tried flexing the chassis as well, no luck.

Is the contour section thumping related, or is this a different problem altogether? It makes a thumping sound at low settings, and nothing in the loudness contour section seems to work.

Kevin Lightner · Post by **Kevin Lightner** » Mon Mar 21, 2005 8:45 am

Sounds like the vco board isn't getting power.
The mixer appears to work, since you get noise.
The vcf appears to work because you get self-oscillations.
The keyboard appears to work because the vcf will track the CV and you're getting a gate causing the thumps.

Thumping is usually due to a misaligned trimmer for for the VCA.
Very easy to adjust, but the back panel must come off.
It can also be broken. Gross temperature changes can also make it thump, but always recalibrate and verify this when the room is at a normal temperature and the unit has been allowed to warm up.

I'd bet that your VCO board has a bad power connector crimp or the board contact(s) are just missing their mating connectors.
I'm assuming you've already verified that changing waveforms doesn't help.

Jeebus · Post by **Jeebus** » Mon Mar 21, 2005 10:05 am

But if the VCO board wasn't getting power, I wouldn't be hearing the oscs. All 3 oscs work, and all the waveforms sound as they should. The overall output is just ridiculously low, except for the A-440 tone which is loud.

I tried adjusting the VCA balance, no change.