There should be something in the menu even if going "outside" the channels
doesn't work. If not my best guess is that the EPROM took a cosmic ray or
something and changed an option byte, telling the micro there is no video
input. I assume there is one physically on the back of the set

I don't know offhand how to set these, you're likely to need a service manual
to find out. I'm not sure, but possibly replacing the EPROM with a model
specific one from Phillips might fix it, or, if you can get into the service
menus on both sets and find the discrepancy you might be able to reset it.

JURB