If I were in your situation I wouldn't touch the existing trim pots.
And, I would use two 10K linear pots or trimpots to fake the missing joystick assembly.
Connect the left and the right side of both pots to -5V and +5V.
And connect the wipers of each to connect pin 1-4B and 1-5B.
This will allow you to set the VCF/DCO modulation to zero as well as pitch bend.
If you use pots you could even make a plate to go over the joystick hole and mount the pots right there.
I still think you should pop a new joystick in there though. LOL
Mike.
From: Gordon J. C. Pearce MM3YEQ <gordon@...>
To: korgpolyex@yahoogroups.com
Sent: Thursday, February 12, 2009 6:44:20 AM
Subject: Re: [korgpolyex] Missing Joystick board (KLM-599) "mod"
On Thu, 2009-02-12 at 08:44 +0000, serotonic_sound wrote:
> Gordon, you said I could potentially wire up a couple of 4.7K resistors... but it looks like
> that board has a few more components, where would I install these resistors exactly given
> that I'm missing the entire joystick assembly and board?
I'll dig out the Poly-800 and draw out the circuit of the joystick board
later today.
Gordon