TI Polar one key not working.........please help

[Orys]

hello,

I finally prurchased a TI Polar and was so happy.
I paid 1200 euro for a used one.
I received the synth today and the first thing i tried was to test the keys.
I noticed that one of the keys is not working and that is the 3rd black key counting right to left.
Why?
The seller says the synth must have been damaged in transit.
What can i do now?
Can i fix it?
I am willing to open it up but where do i look?

Please help me.

Tio