Start with your external power supply. Is it is right voltage and does it have a current rating 300mA or higher?
Then check that the power supply rails in the Poly itself are stable. measure at first power on then measure again a few hours later. Are they stable?
/Mike
From: "ianpoly800@... [korgpolyex]" <korgpolyex@yahoogroups.com>
To: korgpolyex@yahoogroups.com
Sent: Sunday, July 24, 2016 5:12 AM
Subject: [korgpolyex] Re: POLY 800 MKII Drifting
To: korgpolyex@yahoogroups.com
Sent: Sunday, July 24, 2016 5:12 AM
Subject: [korgpolyex] Re: POLY 800 MKII Drifting
I thought I'd update, I never did solve the problem. I ended up bringing the keyboard to a repairman, who thought he'd solved the problem replacing a couple caps, but fast forward $150 in repair hours and the keyboard still drifts. I left it for a week in the same spot and every once in a while would turn it on and watched it fall a few full steps.
The other day I left it on for an hour and a half and it drifted a quarter tone.
Does anyone have any ideas of what I should test in the guts?