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[3rdness]

Hello,

I got a CS01 today at the flea market for $10.  It's a great little synth! Everything seems to work great, but the keys in the middle octave aren't making any sound?

Anybody work on these before?  Any ideas what might be the problem?

I'd love a bit of help...

thanks,

Noam

[samspike]

I've no specific experience with this keyboard, but have encountered a similar problem with other keyboards I've been messing with.

Check if there's a ribbon cable connecting the bit with the keys and key switches to the main circuit board.  One of the connections on that is probably loose or broken.  If you have a multimeter and can access the solder points at opposite ends of the ribbon cable, use that to check.

[Gordonjcp]

The service manual is available with a quick google.  The CS01 uses one big chip to do most of the voice generation and key scanning (it's digital).  If a whole octave has failed, it's probably because one of the multiplex lines isn't being triggered - a look at the diagram shows that the actual notes are wired together with diodes and then each octave is selected in turn.  Check for dry joints or cracks on the PCB, particularly the keyboard one.  Since it's the middle octave and this is where the keyboard is most likely to flex if it takes a hammering, there may be a break somewhere.

The fact that there's not a lot to them is kind of good and kind of bad - there's not much to troubleshoot, but if it's the big unobtainable voice chip that's gone you won't be able to do much with it.  You've got a sweepable filter, I suppose ;-)

[3rdness]

Thanks for the help...

Turns out part of the pcb behind the keys was corroded.  I cleaned it up and bridged the troubled spots.

Now all the keys are working.

What a fun little keyboard!

Do you think I could patch in a line to the filter?

[Gordonjcp]

Take a look at the service manual ;-)

Break in somewhere before the filter, and add some sort of a simple mixer (opamp and a couple of resistors), to minimise the risk of damaging anything.

Whatever you do, don't go down the "traditional" circuit-bending route of randomly bridging wires across stuff.  It's unlikely to get you anything interesting and you stand a good chance of killing the big complicated voice chip.

[alienized]

Hi there,
Has anyone ever tried to add an input before the filter ? (maybe 3rdness since July?...). I'd be very much interested (and secure) if skilled and experienced users could tell me how not to kill this nice synth... 

[Gordonjcp]

Like I said in my previous post, look at the service manual ;-)

The VCF chip is clearly marked, as is the waveform selector.  You'll see there's  couple of resistors and a capacitor that couple the output of the DCO into the VCF - do something similar with your source on the VCF input pin (47K resistor to the pin) and maybe add a little buffer amplifier to isolate your external input from the rest of the synth.

[alienized]

Yes, I'll try that. This circuit is rather simple so it should be feasible...