Korg MS2000 won't stay a semitone up

[dtcmusic]

Hi

A problem has started to happen the last couple of gigs. A couple of songs I had to tune the keyboard up a semitone, then when I went to play it, the keyboard was back in concert pitch. So mid song I went in and tuned it up a step and played it and it was ok, then a bit later it was back down again. I thought maybe it was just a bad night but unfortunately the next gig I did, the same thing was happening. I'm now a nervous wreck on stage, I need to get this sorted but I can't find the problem anywhere online.

Hope someone can help

Thanks