Disklavier

My statement was wrong.

MX series I/o board LED lighting routine.

Main power switch On=all led On.(other than 7 Led.)
Control unit power switch On(no disk)=all Led On from all off.(other than 7)
Disk in=all Led off.
Disk out=all Led on(other than 7)

Please check wiring about external midi connector box and power unit voltage.
Power unit connector 
PIN number 1=+5v
2=+5v
4=+12v
8=+5v

I have I/o ,cpu board and others too.

https://goo.gl/photos/2HCPcVofXueSuotD8