Korg MS20 Mini- Tuning across octaves

[kaidaw]

My Mini will tune both oscilators perfectly, but if I tune C1, C4 will be significantly flat (almost sounding like a B).

The original MS20 had external trim pots to adjust this:

http://www.synfo.nl/servicemanuals/Korg ... MANUAL.pdf

But the mini does not. I've been told that there should be internal trim pots to adjust this and retune my synth, but I can't find any information on how to do this.

Can anyone help?