Korg piano fault-all lights on, unresponsive

[Snailer99]

I have a Korg sp-250 electric piano. It was working fine, then one day I turned it on and all the lights come on and piano won't play. I can hear the amp powering on so that part is ok. Power supply is ok, 12v.
Can't see any obvious faults on the PCB"s, I've pulled all the plugs and re seated them. None of the selector buttons are sticking. I can't enter test mode or anything, the buttons are unresponsive.
What are the common reasons for a fault where all the lights come on?
What else can I test? I have a multi meter and the service manual with circuit diagrams here

https://www.mikrocontroller.net/attachment/493769/korg_sp-250_ServiceManual.pdf

Thanks in advance. Really appreciate any input

 

[vtech]

Sounds like a "system" issue.
Connector CN1 is where most of your LEDs are controlled by a CPLD IC which is obviously latched.
Just about all you can do is to check for all your regulated voltages(3,5,9..etc) on CPU main board. Any of the failed regulators could cause this.
Also there are several oscillators & don't forget the RESET signal and any data line activity(preferably with a scope).
And if they are all there, it is likely you may be facing unobtainable corrupted software?