Korg MS-20 croaked - literally

Discussions about anything analog, digital, MIDI, synth technology, techniques, theories and more.

Korg MS-20 croaked - literally

Postby cloud » Wed Mar 19, 2014 12:54 am

After 35 years of flawless operation my Korg MS-20 croaked - literally. The top two keys issue a low croak that represents somewhere far south of the low end of the keyboard. The remainder of the keyboard is silent. Interestingly, I was about to use it to generate a storm effect, which would probably be fine, but apparently (given that it is now dismantled) this has precedence.

Poking around with a multimeter suggests the keyboard and most of the synth is still functional. The waveforms, scale (16', 8' 4' etc), filters, modulators, EG's white and pink noise sources are all fine. The problem seems to be the frequency being fed to the oscillators. I'm about to start troubleshooting the IC's. If anyone has pointers or had a similar experience, I'm interested in feedback.
cloud
Newbie
Newbie
 
Posts: 7
Joined: Tue Mar 18, 2014 11:51 pm

Advertisement:

Re: Korg MS-20 croaked - literally

Postby HideawayStudio » Wed Mar 19, 2014 6:19 pm

cloud wrote:After 35 years of flawless operation my Korg MS-20 croaked - literally. The top two keys issue a low croak that represents somewhere far south of the low end of the keyboard. The remainder of the keyboard is silent. Interestingly, I was about to use it to generate a storm effect, which would probably be fine, but apparently (given that it is now dismantled) this has precedence.

Poking around with a multimeter suggests the keyboard and most of the synth is still functional. The waveforms, scale (16', 8' 4' etc), filters, modulators, EG's white and pink noise sources are all fine. The problem seems to be the frequency being fed to the oscillators. I'm about to start troubleshooting the IC's. If anyone has pointers or had a similar experience, I'm interested in feedback.

Might just be worth looking at and around IC5 (CA3140) as these sometimes fail leading to crazy pitch related issues (since you have two oscillators playing up it needs to be something common to both of them). If this is ok then try to drive the synth from an external CV. Also look out for dry joints and leaking electrolytics. The latest one I looked at was full of bad solder joints.
H.I.D.E.A.W.A.Y S.T.U.D.I.O
http://www.hideawaystudio.co.uk
The Home of Novachord #346
http://www.novachord.co.uk
User avatar
HideawayStudio
Supporting Member!
Supporting Member!
 
Posts: 1061
Joined: Fri Jan 09, 2009 10:41 pm
Location: UK
Real name: Dan Wilson
Gear: 163 tubes in a large wooden box!
Band: Hideaway Studio

Re: Korg MS-20 croaked - literally

Postby cloud » Thu Mar 20, 2014 10:54 pm

Thanks. Good idea on driving via external CV. It looks like a CA3140 is used for S&H, which is working. I'll do a comparison.

I've seen a lot of comments over the years on dry joints and cap problems but I seem to have been lucky. I bought this synth in 1978 and I've never replaced a thing on it. Even today, when poking around, I'm not finding any voltage or uF irregularities - perhaps due to paranoia over stable power. The MS-20 still operates on its original 240V UK PS but, now in the US, it runs through a transformer. Power in the US is a lot less stable than the UK and I have everything on APC UPS and Belkin Pure AV power conditioners - same as used for computers and home theater.

Using UPS and power conditioning is typical for commercial studios but I'd give it a strong recommendation for home use as well. It's reassuring during brown outs and complete power outages to see everything continue without a blip. During a power outage, you have a chance to bring everything down cleanly. IMHO, it's really worth it.
cloud
Newbie
Newbie
 
Posts: 7
Joined: Tue Mar 18, 2014 11:51 pm

Re: Korg MS-20 croaked - literally

Postby Bitexion » Thu Mar 20, 2014 11:14 pm

Does modulation of the filter produce sound? Try set just noise and filter LFO modulation. If that makes the expected swooshy sound, the CV from the keyboard is borked.

I had that issue with my MS-10 and the tech found that the cable from the keyboard to the VCO pitch was broken. He replaced it and everything worked fine again.
User avatar
Bitexion
Synth Explorer
Synth Explorer
 
Posts: 3402
Joined: Fri Apr 15, 2005 7:43 pm
Location: Drammen, Norway
Gear: Alesis Andromeda A6
Roland D-50
Yamaha Motif XF6
Roland Gaia
Alesis Ion
Analogue Systems modular
+various assorted bits&bobs

Re: Korg MS-20 croaked - literally

Postby cloud » Thu Mar 20, 2014 11:48 pm

Bitexion wrote:Does modulation of the filter produce sound? Try set just noise and filter LFO modulation. If that makes the expected swooshy sound, the CV from the keyboard is borked.

I had that issue with my MS-10 and the tech found that the cable from the keyboard to the VCO pitch was broken. He replaced it and everything worked fine again.


I suspect the cable is fine but that's easy to check, and a longer cable would be really nice :-) Noise sources, modulation, filters and EGs are fine. I actually get sound from the top couple of keys (just way too low frequency) and everything from mixing the VCO's through the rest of the synth is working as expected.
cloud
Newbie
Newbie
 
Posts: 7
Joined: Tue Mar 18, 2014 11:51 pm

Re: Korg MS-20 croaked - literally

Postby Bitexion » Fri Mar 21, 2014 12:21 am

Yeah, just saying there are other options than starting at the IC chip level and looking outwards when it COULD be something as simple as a cable being broken :)
User avatar
Bitexion
Synth Explorer
Synth Explorer
 
Posts: 3402
Joined: Fri Apr 15, 2005 7:43 pm
Location: Drammen, Norway
Gear: Alesis Andromeda A6
Roland D-50
Yamaha Motif XF6
Roland Gaia
Alesis Ion
Analogue Systems modular
+various assorted bits&bobs

Re: Korg MS-20 croaked - literally

Postby chimney chop » Fri Mar 21, 2014 2:39 am

Watch on youtube.com
User avatar
chimney chop
Junior Member
Junior Member
 
Posts: 227
Joined: Wed Aug 10, 2011 5:46 am
Location: Brooklyn, NY
Gear: plugiator
access ti2
nord stage 2


Return to General Synthesizers

Who is online

Users browsing this forum: Baidu [Spider] and 7 guests