I was re-installing the keybed in my EPS and when I switched it on, several of the buttons weren’t responding. I switched the machine off, unplugged and re-plugged both cables from the front panel board, and now it doesn’t display anything on the VFD until you press a button, at which point it will display one character in the first space, which changes with different button presses.
The instrument LEDs light up correctly, it reads the OS from the boot disk in the normal amount of time, but nothing on the display but the one meaningless character.
It was working perfectly the previous time I switched it on, which was thirty seconds prior. Between switching it on and everything functioning and the first malfunctioning of the buttons, I didn’t touch the front panel board or any of the internals except to plug in the KPC (on the keybed end, not the mainboard end, so I didn’t touch the mainboard at all).