Roland KR 4500 - Panel Locked Up

System powers up, all lights on the main panel light up and stay lit, display panel is lit but blank, no sound obviously, just some humming. No schematics available via online searches. I am assuming one of the boards need to be replaced, not sure which one. Can anyone help?

Thanks,

Ray

Is here - checked and working as of just now.

https://gozofinder.com/cse/ulozto/cz?query=kr-4500