Discussion about the Korg PolySix synthesizer

I recently had my Polysix KLM-367 board serviced through Old Crow (replacement, rather) 
and just got it back a few days ago.  Unfortunately I needed to re-calibrate the oscillators 
and tune them since it sat for so long not being used.  But the tuning is still off - not really 
a seperate oscillator problem so much as I can't get it to the right pitch using the tune 
knob.  Even at the max to the right (sharp) I cannot get the unit to hit a perfect a-440.  
And just to clear up the dummy-factor, I even made sure that the tune knob was set at 
dead-center when I began the oscillator tuning, so i would have flexibility in both 
directions if the tuning shifted.  I am about to re-do the process but I am curious if 
anyone else has suggestions as to why this may happen even though I kept the pot at the 
center?  Any help is appreciated, thanks.

~Mike