A quick Google search brought up these sites with a few pictures but no additional info:
https://musicsklep.pl/keyboardy/ketron-event.html

(Click picture to enlarge)

and here:
https://klawiszowe.pl/ketron-event-p-4980.html
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Cheers 🥂
GJ
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"Success is not counted by how high you have climbed
but by how many you brought with you." (Wil Rose)