[sdiy] Korg Polysix - now weirdness

Tom Wiltshire tom at electricdruid.net
Wed Nov 19 22:47:24 CET 2008

On 19 Nov 2008, at 20:11, David Anderson wrote:
> I believe the Polysix uses a scanned matrix keyboard.

It does.

> If you short pins on the connector (depending on the pins) you  
> should expect sound. Depending on how many (and which ones) you'll  
> get multiple notes.

I don't quite see why you should get multiple notes, but I'm prepared  
to believe I'm just being slow if you're both sure. I'm feeling quite  
slow. Be sure that you are certain this is right.

> This is a good thing: it demonstrates that everything between the  
> keyboard connector to the 1/4" out works properly (assuming nothing  
> else is bad). It also points to the key mechanism as the actual  
> problem.
> If they keyboard itself is not working, I can think of several  
> immediate candidates:
> - the bus wire that is the keyswitch mechanism
> - the diodes on the keyboard

As Karl no doubt knows, the Polysix has no buswire, being one of  
those keyboards which is based around conductive rubber buttons which  
short interlocking "fingers" etched on the PCB. It's a hideously  
unreliable system, at least in the Polysix. The similar keyboard on  
my SH101 has had far less trouble.

> Test the keyboard itself: make sure that a key press results in an  
> actual electrical switch closure.

Good advice. Get a multimeter on the connector and test the keyboard  
separate from the synth. The keyboard consists of groups of 8 notes  
labelled "DB0", "DB1", etc. The top group only uses 5 of it's eight  
connections (8x8=64, 61 note keyboard)
The socket on the PCB for the keyboard connector is helpfully  
labelled with the DB groups and the port numbers. You can buzz  
between a group pin ("DBx") and a port pin ("Px").

Good luck!


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