[sdiy] unstable Korg MS 50 vco

[ganesha]

Thanks to everyone for the advice. 

I'm going to open it this weekend to check for any problems in the exponential converter area.

I'll let you know if I find anything.



----- Original Message -----
From: Dave Magnuson <kingravine at comcast.net>
To: 'ganesha' <goaqihai at yahoo.co.uk>; synth-diy at dropmix.xs4all.nl
Cc: 
Sent: Thursday, 2 February 2012, 21:51
Subject: RE: [sdiy] unstable Korg MS 50 vco



-----Original Message-----
From: synth-diy-bounces at dropmix.xs4all.nl
[mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of ganesha
Sent: Thursday, February 02, 2012 3:00 PM
To: synth-diy at dropmix.xs4all.nl
Subject: [sdiy] unstable Korg MS 50 vco

Hi,

I recently bought a Korg MS 50 but I noticed that the VCO is very unstable
for the first 10 minutes after I turn it on. It's not just detuning but it
really jumps from high to low notes and vice versa.

This is the case with both the HZ/V and OCT/V inputs. After 10 minutes,
there is no problem anymore.

I've checked the schematics. Could it be the 2SC1583 that is causing this?


http://www.korganalogue.net/korgms/service/ms50/ms50schemos.pdf

Thanks.

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Since your problem goes away after warm-up, I'd suspect a "thermal" related
problem.  Something could be warming up, expanding, and making better
contact.

So the first thing to look for is cracked/cold solder joints near the VCO,
loose wiring harnesses, etc.  It could also be a hairline crack in one of
the circuit board traces

Sometimes I'll just re-touch all of the solder joints on the board in that
region with a tiny dab of new solder, making sure the old solder melts and
re-flows

Dave Magnuson