[sdiy] Korg Polysix - now weirdness

Tom Wiltshire tom at electricdruid.net
Thu Nov 20 11:06:05 CET 2008

> It turns out that the dude who "repaired" the polysix before me  
> managed to install each and every diode in the scanning matrix  
> backwards... ...wow...

Yikes! What on earth was he trying to repair that involved replacing  
all the keyboard matrix diodes?

> Anyway it's supposeably "working" now but now i'm in tuning-hell. I  
> managed to get all voices to tune up fairly well despite the  
> service manuals pretty crappy description (by "Play C6 and adjust  
> VR11 to 0Cent" they mean 4186hZ - right?) except for one voice that  
> totally refuses. Basically there's no more "turn" on the low-tune  
> pot and i cannot get it to work. Does it seem like my Oscillator #3  
> (that refuses to tune) is busted somehow to anyone but me?

Not if it's running. I'd check that the tuning pots and associated  
resistors for that voice are ok, and then look at the capacitors.
I've seen a dead voice due to a transistor failure, but that killed  
it stone dead, not just a tuning problem.

> Furthermore the service manual doesn't mention VR14 (D#4-E4 ADJ) or  
> VR15 (tune mid). Also, the switch which is talked about on tuning  
> step 1: "Change circuit board slide switch to opposite position  
> (away from VR1)" doesn't seem to change anything, i'm guessing  
> "away from VR1" means the back position, towards the rear. VR1, VR3  
> and VR15 also makes the pitch "slide" when i turn them, but i'm  
> guessing that's normal. VR14 (D#4-E4 ADJ) doesn't seem to be  
> affecting much of anything.

I've never attempted to tune the Polysix according to the service  
manual. It's a nightmare. Instead, I've always found judicious  
adjustment only where strictly necessary to be a better policy. Once  
you start twiddling everything, you're pretty much committed to a  
complete retune.

Good luck,

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