Kawai Synthesizers

I just purchased a used K4 and something's wrong with the LCD. I turn 
on the synth, and 16 solid black squares are displayed in the top row, 
nothing in the bottom row. However, the buttons and sounds work fine. 
I downloaded the manual from the Kawai website, but couldn't find 
anything. Has anyone had a similar problem, or does anyone know how to 
fix this?

Any help would be greatly appreciated!

David S.