Discussion about the Korg PolySix synthesizer

I tuned my Polysix about 5 years ago. The other night, trying to tune
up to a melodica, which is in correct tuning, I had to turn the tuning
knob all the way to the left and even turn the pitch wheel up a bit to
get it in standard tuning. Is this to be expected, do I simply have to
get in there again and fiddle with the internal tuning posts or do I
have a bigger problem? Thanks for the input!