HP8751A boot failed

[mrf245]

Hello
I have HP8751A worked fine before,now it can't boot up normally.
When power-on,I can hearing internal relay sounds"da,da",CH1 led turns on,but display still nothing,and floppy drive no responce(normally,I can see floppy drive LED turns on and hear sound from it).
When I open case,dismatle CPU board cover and power-on,I can see main and sub CPU board status LEDs go on,finally they stop in some combination(tomorrow I post my CPU LED status photo here),I wonder if anyone know what's meaning or where I should check(I have no found service manual from google)? Thanks.