Korg PA80 hang on booting OS "wait please

[Agrasso71]

Hi, I've a PA80 with some problem(s)
At first it doesn't boot Os. The screen show 'korg pa 80 wait please" at power on. I try many key combination as I have service manual but the result is the same.
Of course I try to relod OS by a floppy disk by pressing fadein key at power on but the boot it's stopped anytime with message 'error reading bootsys'

I try to measure the voltage at the out of the power amplifier and it's show 8 5 -8 as I aspected.
Any suggest please?
Thank you very much
(Sorry for my poor english I'm from Italiy..Napoli)