AW: cs-50

[Haible Juergen]

	>I recently purchased a Yamaha CS-50 for £40 (uk sterling). A
bargain?

Absolutely. I'd pay that price for a completely non-working
(but physically intact) one without hesitation. (I'd even pay that
for the mere keyboard action, if it's mint condition ...)

	>The only problem with it is that a high pitched noise starts after
about
	>15 minutes of switching on. It is independent of the volume
controls,
	>and sounds the same as when pressing the highest key with the sine
wave
	>an octave up. I assume somehow this setting is shorting to the
output.
	>Does anyone have any ideas before I take a look inside? It makes
some
	>great sounds but it's getting really annoying.

Hmm, I'm quite bad on repair stuff (modifying is much more my
deal), but anyway, a few guesses:

You don't have the Ring Modulator on all the time ?
("Off" means that the Modulation Slider is UP, not down !!)
The 15 minute delay is strange, though ...
Your Ring modulator sliders might have an intermittent contact ...
Does the pitch change, if you alter the ring modulator frequency ?

If it's not the Ring mod, it might be one of the voices. Does the pitch
change if you play a four-fingered chord in the lower range ?
If so, the VCA might leak. If not, you would have a leaking VCA
*and* a stuck pitch CV or bad VCO at the same time. Not
likely, but possible ...

That's all that comes to mind at the moment. Next step should
be a careful inspection of the interior, loose wires, conductive
objects stuck between the boards, that stuff.

If you have to trace the error thru the circuit, Yamaha still sell service
manuals.

Good luck !

JH.