[sdiy] MS20 & MS50 problems

[Peter Snow]

Hi All,

I need some advice for problems I am having with my Korg MS20 & MS50. I have to sell these
units and there are a couple of small problems that need attention. Before I rip them
apart and risk doing untold damage, I thought I would run it by the gurus on the list.

1) On the MS20 when I press a key the note sounds, but immediately on releasing the key
the note drops a minute amount.
I am old, tone deaf and have tin ears so I cannot hear it very well, but someone much
younger pointed it out and a digital tuner confirms that there is indeed a slight drop in
pitch. 

My first thought was the keyboard voltage sample & hold, a leaky FET or capacitor? Does
this sound feasible? Does anyone know if this is a common problem with these units?  The
keyboard itself seems OK - I took it out and cleaned it up.  Didn't help with the problem
tho'.

2) The pitch on the VCO of the MS50 seems to be constantly modulated by the LFO.  Again
the effect is slight, but noticeable. My guess would be that the LFO chips need bypass
caps on the power supply pins or the ones already there(?) need replacing. Does this sound
possible?

Generally speaking, can anyone give me an idea of how difficult it is to work on these
synths?  I have schems of the MS20 that I downloaded from the 'net, but none for the MS50
- does anyone know where I can find them?

Any help greatly appreciated.

Thanks,

Peter