Roland KR-770 intermediate sound problem, possibly a bad board?

Hi Friends, I have a Roland KR-770 weighted key piano, when I press the power button it lights up and everything appears to be fine, the problem is 50% of the time the keys will make no sound, 50% it works fine. sometime turning it off and on again works and sound come through, sometimes not for days.
I had a local tech come and jiggle all of the connections internally (just like I did before I called him) and he said its not the amp, the mother board is dying. its very hard to find a replacement board and usually they are over a thousand dollars. is there another answer? or does anyone have a board I could buy? thanks