Korg Mono/Poly

Hi guys,
I have a problem with my Mono/Poly where vcos 3 and 4 are both out of tune by about 2 semitones - ie. when vcos 1 and 2 are playing a C, vcos 3 and 4 are playing a Bb. I did hear them step back in tune but it was quite brief and then they abruptly went out of tune again. Is this a take it to the synth repair guy thing or something I can remedy with my own fairly limited electronics knowledge?

Thanks,
Dave