Vintage Synth Repair

> Please keep in mind I'm new to troubleshooting and repairing 
vintage 
> synths..
> 
> I recently acquired a CS-50.  It has 2 problems though: the touch-
> sensitivity is not working and one of the voice cards tracks the 
> keyboard, but with a pitch about 4 or 5 octaves above the other 
> voices-- this voice squeeks instead of squaking.....<<

I just acquired one of these magnificent baby elephants myself, from 
the unlikely source of a touring air-force band in the US. mine works 
fine, but needs a bit of a tune-up. actually, I'm amazed at the great 
shape it's in, especially after reading the various apocrypha that 
attends it's near-relative, the cs80. & it made it to the UK in one 
lump too.

I have the schemo's (yamaha in the UK were able to supply them from 
stock!) if a scan or copy would be any use. they've also been very 
good at parts for older machines too- I got a vco, vcf, a replacement 
key & some other bits for my cs30 without any trouble.
 
tbh, I was rather hoping that the cs50's manual would include a 
quickie service procedure but it doesn't. it seems rather to rely on 
one's native wit as an electronics engineer- "here are the diagrams, 
now figure it out" sort of thing.

but going back to your first query- I would suspect (after a brief 
perusal of my schemo, which I only got yesterday!) that you've got a 
duff transpose circuit on that voice card. 
if it tracks ok but is several octaves higher then what's most likely 
failed is the "transpose" function, a separate control-input to the 
actual vco chip. this voltage is generated individually on all four 
voice cards. start by checking/comparing the voltages on IC8/pin 1 on 
the four cards.
octave switching is accomplished by switchgear made up of FETs 1-4, 
transistors 1-5, VR1, 4, 5 & 6, & IC7 (in a little tin). this 
switchgear is controlled by the states of connectors 15, 16, 17 & 18 
(adjacent to the FETs, & coloured red, orange, yellow & green 
respectively), while CP6 on the same board-edge is used to check the 
action of the transpose function. the control voltages are all from 
the front panel range switchgear- I guess it was just easier for them 
to develop boards with the switching done locally rather than a 
master transpose board somewhere- one eye on the future & the cs80, 
maybe?


& you need to check the condition of the lamp & ldr that yamaha use 
to work the aftertouch. the pre-amp that follows the ldr is a 4558, 
common enough. after this, the aftertouch volts go their separate 
ways, so it's not likely to be anything else since these settings 
aren't part of the preset/panel switching.

hth.

'pon this latter- I just got a roland sh2000 yesterday too. this also 
has a crude but effective aftertouch, which seems to be based on hall 
effect instead of optical techniques. anyone know about this?

duncan/radio massacre international