Discussion about the Korg PolySix synthesizer

Hi!

 My Polysix has had its screws put back in place and I've only been 
making sounds with it for a while. It mostly works more or less as it 
should. At times something happens to the signal level and something 
sounds like erratically auto-oscillating analog stages. I had this 
when I first unpacked it too and never really found out where the 
problem was, but I suppose a dirty/bad connector or a bad solder 
joint or some other intermittant connection somewhere. Of course I 
have a scope so it should be possible to find the source of the 
problem. It's definitely not in the digital section, as power down/up
doesn't make a difference.

 The trickier problem I face is that the "VCA" setting of the MG MOD 
switch doesn't work - but I think it did for a very brief period. 
Both VCF and VCO settings work as they should, just not the VCA 
setting. I've studied the diagrams but it looks to me like the switch 
data from the MG MOD selector is tangled up with everything else 
that comes from the control panels (of which everything works!) so I 
need to come up with a way to pin down this problem. 
 In the diagram it looks like the bottom setting of the MG MOD switch
(set to "VCA"??) is not used electrically so I take it there's 
nothing wrong with the switch itself and that the logic on the KLM-
367 is meant to sort this out...?

 Any suggestions on how to find the problem with the "VCA" MG MOD?

TIA,

Thomas