[sdiy] Korg Polysix - now weirdness

David Anderson andersdl at buffalo.edu
Wed Nov 19 21:11:54 CET 2008


Karl Ekdahl wrote:
> So i installed new processors in the polysix (thanks peter!), but to
> no avail. In my desperation however i disconnected the keyboard
> connector and tried shorting the different pins together - Sound!! Of
> course i got multiple notes playing but at least the things was doing
> *something*. I wondered if the diodes were blown or put in the wrong
> way, but the only way i can get it to work is by bypassing the diodes
> or putting them in the wrong way - which of course yields multiple
> notes, again. So what the hell is going on?? I'm now considering
> whether ALL the pull-up resistors to the keyboard could be blown??

I believe the Polysix uses a scanned matrix keyboard. 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.

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

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

The circuit diagram for this synth might help you understand the matrix 
keyboard:
http://www.synthdiy.com/show/?id=4142



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