Korg MS-20 Problem - Possibly VCA

Gonecat

I have a first-version MS-20 and I have to crank it up to 10 to hear much, VCO's and Filters are working. No patching is being done. Went out all of a sudden, didn't get moved or banged.

I have been following Delton Horn's troubleshooting book and it says it might be a bad capacitor.

Any thoughts on what to check first?

MS-20 schematic: (VCA is at far right, look for c32-c35)
http://www.korganalogue.net/korgms/images/service/ms20/circ1.gif

MS-20 "Style" VCA for another view:
http://members.tripod.com/urekarm/synth/jx_vca.pdf

Thanks for any help on this...

Gonecat · Posted: Sun May 03, 2009 4:06 pm Post subject: FIXED!

Groovy!

It's fixed.

Opened it up and saw R126 (680k) in the amp circuit was sheered off at the top.

Soldered a replacement to the back of the board and lo and behold.

When i saw the sheered off resistor, it made me think of looking to see if they were in series or parallel since if in parallel the extra resisitor would allow MORE electricity to pass. Indeed it was.

Remaining question:

Any probs with leaving the sheered resistor there? (i spread the leads apart).

I got lucky on this one. It's kinda like your car breaking down and you open the hood looking for basically a big On/Off switch you can throw back to 'on'.

Blue Hell · Posted: Sun May 03, 2009 4:36 pm Post subject: Re: FIXED!

Gonecat · Posted: Mon May 04, 2009 5:44 pm Post subject:

Definitely - i dislike unanswered posts! Smile

I could just be really happy to have the MS-20 back in action, but it sounds a lot cleaner and louder now than it was before. I suppose it's just resisitors getting old.

I am wondering what other components if replaced would also yield some better results!

Thanks for the friendly welcome - getting a lot of mileage out of your site already...

Smile