OldSynths

Hi all,

Please keep in mind I'm new to troubleshooting and repairing vintage
synths, also I have posted a similar msg to other groups, so I
apologize for any repetition..

I recently acquired a CS-50. I really love the unique sound of this
synth and can't wait to record it. 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 squeaks instead of squaking.

Since I have 3 perfectly fine voice cards, I figure I can use one of
those to pinpoint the problem in the faulty card. I'm armed with a
radioshack volt-meter, but I'm not sure where to go from here.
Would the best method be to measure voltage between components and
do a one to one comparison? Say, if the voltage differs in the same
point on both cards, I would know the problem is in that area and I
could simply replace that component? Does this sound like the right
strategy? Unfortunately I don't have any schematics, and only a
partial service manual for the cs-80 is on the web (nothing on the
voice boards). I'd appreciate any tips/suggestions. Thanks.

hi
you can find an owners manual here
http://www2.yamaha.co.jp/manual/english/download2.php
no schematic tho.
the touch sensitivity is not quite a regular arrangement - you can
read up on how it works in the manual, maybe it is working but just
not what you expect.

it may not be a good idea to go poking around, power on, without the
schematic, too easy to fry things.
you could look for obvious faults (unplugged) - loose wires or broken
solder joints, burnt out components.
old analogs can get out of tune...tho 4-5octs is a worry.
hope this is a start.
andrew

--- In oldsynths@yahoogroups.com, "zendenker" <doof@c...> wrote:
> Hi all,
>
> Please keep in mind I'm new to troubleshooting and repairing vintage
> synths, also I have posted a similar msg to other groups, so I
> apologize for any repetition..
>
> I recently acquired a CS-50. I really love the unique sound of this
> synth and can't wait to record it. 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 squeaks instead of squaking.
>
> Since I have 3 perfectly fine voice cards, I figure I can use one of
> those to pinpoint the problem in the faulty card. I'm armed with a
> radioshack volt-meter, but I'm not sure where to go from here.
> Would the best method be to measure voltage between components and
> do a one to one comparison? Say, if the voltage differs in the same
> point on both cards, I would know the problem is in that area and I
> could simply replace that component? Does this sound like the right
> strategy? Unfortunately I don't have any schematics, and only a
> partial service manual for the cs-80 is on the web (nothing on the
> voice boards). I'd appreciate any tips/suggestions. Thanks.

It sounds like that voice card has a broken octave select circuit.
They call it the transposition gating circuit in the service manual. My
offhand guess is one of the FETs went bad (one of FET1 through FET4) on
the affected board and is holding the highest octave selection "on" all
the time. The circuit for the "M" boards of the CS-80 is 99% the same as
that for the CS-50; there are only a few resistor values changed, and a
few omitted parts (the CS-50 does not have the stops for fifths, only
octaves).

As for the touch response, check to make sure the light source (a small
12V or 16V bulb--24V will also work) under the keyboard itself is not
burnt out. It is mounted under the left end of the keyboard keys and is
covered by a pull-off rubber housing. It should be lit whenever the power
is on. Note that the keyboard is on hinges similar to the main lid; just
loosen two screws on the underside of the case and the keyboard will swing
up into a vertical position.

Crow
/**/

On Thu, 5 Aug 2004, zendenker wrote:

> I recently acquired a CS-50. I really love the unique sound of this
> synth and can't wait to record it. 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 squeaks instead of squaking.

I have a Korg Wavestation that appears to work fine with one exception-
the keys dont trigger any sound in the area of middle C to the octave
below.
I am not familiar with Korg so any help in this area would be
appreciated.
All other aspects of the synth seem to be OK.

Thanks
Rory McDonald
OldSynths Moderator

Thanks for the response Crow, it was very helpful.

As it turns out the light under the keyboard was burned out. Also,
I didn't realize just how hard you need to press on the keyboard to
get the touch response to open up, definitely not feather-light
response as in many of todays keyboards. In case it's of interest
to anyone: the lamp is a Toshiba marked A24V5W.

I've found a source for the service manual and it should be in the
mail this week, but I went ahead and ordered a handful 2SK30 FETS to
replace the ones on the ailing voice board. Maybe that'll do it,
and the problem will be fixed even before the service manual gets
here.. Anyway, thanks again. I'll be sure to update for the archive.

> It sounds like that voice card has a broken octave select

circuit.

> They call it the transposition gating circuit in the service

manual. My

> offhand guess is one of the FETs went bad (one of FET1 through

FET4) on

> the affected board and is holding the highest octave

selection "on" all

> the time. The circuit for the "M" boards of the CS-80 is 99% the

same as

> that for the CS-50; there are only a few resistor values changed,

and a

> few omitted parts (the CS-50 does not have the stops for fifths,

only

> octaves).
>
> As for the touch response, check to make sure the light source

(a small

> 12V or 16V bulb--24V will also work) under the keyboard itself is

not

> burnt out. It is mounted under the left end of the keyboard keys

and is

> covered by a pull-off rubber housing. It should be lit whenever

the power

> is on. Note that the keyboard is on hinges similar to the main

lid; just

> loosen two screws on the underside of the case and the keyboard

will swing

> up into a vertical position.
>
> Crow
> /**/
>
>
> On Thu, 5 Aug 2004, zendenker wrote:
>
> > I recently acquired a CS-50. I really love the unique sound of

this

> > synth and can't wait to record it. 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 squeaks instead of squaking.