Discussion about the Korg PolySix synthesizer

Hi, I'm new to this group and this is my first message.

I recently got a Polysix (about 2 months ago). Everything was working fine with my unit but about a week ago one of the voices had drifted out of tune. I opened up the synth and tried to tune it with the help of my brother, who is a bit more knowledgable about electronics than I am, and with the help of the service manual.

I tried tuning the voice but no matter what I did I couldn't get it in tune over the different octaves. If it's in tune in the higher octave it sounds like crap in the lower and vice versa. I know there is two resistors to turn, the Tune High and Tune Low, but I don't really know what I'm doing when I'm turning these. Following the instructions of tuning in the service manual got it even worse out of tune. So I don't really know what to do.

Maybe I'm doing something completely wrong, I don't know. I've tried getting info on this on the web but with no luck. So now I turn to you.
Maybe someone can help me with my problem? It would be greatly appriciated. 

/Lukas