Could be due to the fact that he has checked the fuse's and the panel doesn't stay on when the mains is removed.
Not a panel fault more the smart rio inside the 500
I think you have badly designed your system, using rios to reduce runs only makes sense and saves money if you have 8 circuits that are 100m away from the panel.
A GD48 would have give you 16zones onboard and 4 rios and the software on the panel is more suited to a home then a 500/520 which are aimed more at high security installations that need other things.
if its a 500 check the ribbon cable from psu to main board.
Galaxy D 520 is the equivalent to a 500, you will need a small fortune to replace, how many circuits you using ? a GD48 will probably do