Hi John ,
So sorry to read about your problems.
I remember way back in 2004 , my kn7 died after a bad power failure, ( tree hit power line and the power slowly went down along with the keyboard)

Anyway figured must be the end, BUT, ( I think the guys name wasTechnics Player?) on the technic forum, he gave me a list of things to do, and the keyboard was back good as ever. I basically had nothing to lose.

Is it possible some sort of reset might help or is it a physical problem.