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Micromoog: bypass problem

Posted: Wed Dec 09, 2009 8:54 pm
by dogcontrol
Anyone feeling helpful?

My Micromoog is malfunctioning unfortunately. The symptom of the problem is with the bypass function, but it could originate in another part of synth for all I know. Bypass holds the internal VCA on constantly, to produce continuous sound output (whether keys are depressed or not). When it is switched ON, the continuous tone is heard, when it is switched OFF the oscillator *should* be routed to the Loudness Contour Generator (which appears to be working in the Sample & Hold function).

So the problem is that in the "off" position I do not hear sound, although in the "on" position the constant audio output of the VCO persists. When I first bought this thing, it worked fine and I could play it like a normal keyboard (making a sound as long as a key is depressed). A friend of mine told me the switch is probably broken and should be replaced, but could it be a connection somewhere else that has gone bad or come loose? I also noticed that one of the two fuses is missing, could this cause problems? Before I arbitrarily agree with the former guess and start carving up my micromoog, I wanted to share this with you all and ask if any of this makes sense, reminds you of any other similar problems. Is there anything else that could cause this? Something higher up on the chain. Are there any ways to test what could be causing the problem?

Also, if it is the switch that needs to be replaced, what is the best way to remove a switch with six solder terminals? Should I use a desoldering braid to remove the solder and then try to carefully extract the switch? Would this heat up any parts of the circuit board to the point where I should use a heat sink?

Anything helps, thanks a lot!


Re: Micromoog: bypass problem

Posted: Sat Dec 12, 2009 2:46 am
by Maschinengeist
Will try to unfolder my service manual and have a look at it, during the weekend. Don't hold your breath, I've got a lot to do these days.

Re: Micromoog: bypass problem

Posted: Sun Dec 13, 2009 5:54 pm
by dogcontrol
Excellent! thanks, anything helps!

Re: Micromoog: bypass problem

Posted: Sat Jan 09, 2010 1:10 am
by sqweebking
Ive got a service manual here in front of me and it looks like your problem would lay in the bypass switch itself or the contour generator. Id probably test the switch first, you should have continuity between pins 1/4 and 2/5 when in the off position, or pins 2/5 and 3/6 in the on position. From there the signal goes to the contour generator and there are quite a few test points.

Re: Micromoog: bypass problem

Posted: Sat Jan 09, 2010 3:49 am
by WhinyLittleRunt
I agree also it is likely the switch itself. I have had this problem when switching the filter tones and when putting the switch back to normal it doesn't work unless I mess with the switch...

Re: Micromoog: bypass problem

Posted: Sat Jan 09, 2010 7:48 am
by nadafarms
yes those switches suck, I had a micromoog that would only go into self oscillation "full tone" occasionally if the switch felt like switching that day.

Re: Micromoog: bypass problem

Posted: Thu Jan 01, 2015 7:15 pm
by BigJoeScientist
Hello. Where would I find a replacement Bypass switch? The diagram indicates that this is a 2P3T switch, but I wonder if that might be a typo... on inspection, the switch seems to be a 2P2T. If I can't find a suitable replacement, I may try to rebuild the switch... a fools errand?