[sdiy] Yamaha CS-50 high pitched voice

[WeAreAs1 at aol.com]

In a message dated 7/4/04 2:21:45 PM, doof at cox.net writes:

<< I recently acquired a nice CS-50 cheaply, but alas the voices are not 
completely in tune (surprise, surprise).  Is anyone here familiar with the tuning 
procedure? I've found the CS-80 procedure on the web but I'm not sure how 
applicable it is to the 50.  The particular symptom that has cropped up is that 
the fourth voice has an extremely high pitch when played.  Any ideas/pointers?  
Thanks. >>

Hello,

Congratulations on getting your cool synth!  I can't help with the tuning 
procedure, but I have a couple of tips on troubleshotting that one bad voice.  
You should try swapping out the bad voice card with another known good voice 
card (for instance, if voice #4 is bad, then switch it with the #1 voice card).  
If the high pitch problem moves with the card, then you will know that the 
trouble is on the actual voice card.  If the high pitch problem stays at the 
voice #4 position, then you will know that the #4 voice card is OK, and that your 
problem is somewhere further downstream (upstream?) from the voice card - 
perhaps at one of the voice CV demultiplexers (probably a 4051, 4016, or 4066 IC 
and an opamp or two).  If, by doing this procedure, you can determine that the 
#4 voice card is indeed bad, then you might consider swapping out the VCO IC 
from the bad voice and trying one of the VCO chips from another known good 
voice card.  This will be easy if the IC's are already in sockets, and a little 
tougher if the IC's are soldered in place.  If you can determine that the VCO IC 
is bad, then you'll be searching around for a while to get a replacement IC, 
unfortunately (Yamaha no longer supplies the part).  BTW, make sure the power 
is turned OFF when doing any of this voice card or IC swapping, or you could 
create some further problems for the synth.

Michael Bacich