Back in the day, I had that same problem. With me, it was a hardware problem, not a very complicated fix as I remember.
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> To: korgpolyex@yahoogroups.com
> From: korgpolyex@yahoogroups.com
> Date: Tue, 6 Oct 2015 16:45:36 +0900
> Subject: Re: [korgpolyex] POLY 800 MKII Drifting
>
>
>
> If all voltages are OK, then problem is in different part of
> instrument. Still I'd suppose it's hardware, not software problem.
>
> I'm quite sure more experienced members here would know what can be the
> cause for this and how to repair.
>
> Daniel Forro
>
>
> On Oct 6, 2015, at 4:39 PM,
> ianpoly800@...<mailto:ianpoly800@...> [korgpolyex] wrote:
>
>
>
> thanks for the reply!
> thats super frustrating.
> I don't think that's it though, I only use a power supply, I checked
> and it's steady :(
>
>
>