Vintage Synth Repair

Hi All!!!

I�m a synthesist from Finland and am a brand new member here. Have a lots of analog and digital gear, mainly from the 70�s and 80�s. So I have to do quite a bit of maintenance and am very willing to share my experiences to help others if possible.

Now my trusty old Micromoog from 1976 has failed and I am at loss to localise the problem. Noise, filter, and modulation work just fine, but the actual sound-producing oscillator is dead. I have heard that some people have fixed their micromoogs by replacing some op amps, but I really would like to know where to start looking. I have the service manual and have replaced a couple of bits listed as possible reasons in the troubleshooting guide. This resulted in the filter, VCA, and modulation coming back to life, but no oscillator sound.

It seems to get more complicated next, so I would very much like to hear if someone of the listees has fixed the oscilltor and what was the problem in your case...

cheers and thanks in advance,

Ami

Check the CA3080 chips.
But beware: sometimes putting in a modern CA3080 will not help: you  
need a 3080 tested to be within a specific range.
Since you mention that noise works: I have had success swapping the  
3080 from the noise to the VCO, and putting in a new 3080 into the  
noise section.

> Now my trusty old Micromoog from 1976 has failed and I am at loss to  
> localise the problem. Noise, filter, and modulation work just fine,  
> but the actual sound-producing oscillator is dead. I have heard that  
> some people have fixed their micromoogs by replacing some op amps,  
> but I really would like to know where to start looking. I have the  
> service manual and have replaced a couple of bits listed as possible  
> reasons in the troubleshooting guide. This resulted in the filter,  
> VCA, and modulation coming back to life, but no oscillator sound.
>
> It seems to get more complicated next, so I would very much like to  
> hear if someone of the listees has fixed the oscilltor and what was  
> the problem in your case...
>
> cheers and thanks in advance,
>
> Ami
> 
>

Terje Winther
terje.winther@...
http://www.wintherstormer.no/

Thanks Terje!!!

Must check that one and the swapping idea is a clever one :)  I´ll let you know how it turned out...

cheers,
Ami

--- In vintagesynthrepair@yahoogroups.com, Terje Winther <terje.winther@...> wrote:

>
> Check the CA3080 chips.
> But beware: sometimes putting in a modern CA3080 will not help: you  
> need a 3080 tested to be within a specific range.
> Since you mention that noise works: I have had success swapping the  
> 3080 from the noise to the VCO, and putting in a new 3080 into the  
> noise section.
> 
> > Now my trusty old Micromoog from 1976 has failed and I am at loss to  
> > localise the problem. Noise, filter, and modulation work just fine,  
> > but the actual sound-producing oscillator is dead. I have heard that  
> > some people have fixed their micromoogs by replacing some op amps,  
> > but I really would like to know where to start looking. I have the  
> > service manual and have replaced a couple of bits listed as possible  
> > reasons in the troubleshooting guide. This resulted in the filter,  
> > VCA, and modulation coming back to life, but no oscillator sound.
> >
> > It seems to get more complicated next, so I would very much like to  
> > hear if someone of the listees has fixed the oscilltor and what was  
> > the problem in your case...
> >
> > cheers and thanks in advance,
> >
> > Ami
> > 
> >
> 
> Terje Winther
> terje.winther@...
> http://www.wintherstormer.no/
>

Thanks Steve and Terje!

It was IC 401 and one failed FET... now it is alive and well again. Well, the S/H doesn´t sample or hold, but I can live with that :)

cheers,
Ami



--- In vintagesynthrepair@yahoogroups.com, Stephen Jones <thirteentech@...> wrote:

>
> Check that your current source (IC304) is OK by seeing if you are getting a CV out from the jack on the back of the synth. Check that R401 isn't open circuit. Otherwise check IC 401 and 402.
>