Check all of the keys and switches. Which ones work and which ones don't. Also, check all of the keyboard keys. Which ones work and which ones don't.
Write them out in a table and share it with us.
/Mike
From: "andrey.koikto@... [korgpolyex]" <korgpolyex@yahoogroups.com>
To: korgpolyex@yahoogroups.com
Sent: Thursday, October 6, 2016 2:35 AM
Subject: [korgpolyex] Re: stuck in sequencer mode
To: korgpolyex@yahoogroups.com
Sent: Thursday, October 6, 2016 2:35 AM
Subject: [korgpolyex] Re: stuck in sequencer mode
Thank you, Mike, that was helpful for me also. I have almost the same issue: Poly800 frozen right after powering up with "1 50 01" display with no sound and reaction to any buttons or keys. Could you please tell me how to check if the IC33 is broken? Thanks!