> 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