@AmiNeo
A red screen is not nessasary a BAD rom - infact in the A1200 a BAD rom is normally a black screen.
A red screen is usually reserved for problems with devices that fail auto config / initilization state - like accelerators / adapters - zorro cards etc.
Its important to understand the A1200 is a completely different beast of a machine than that of the A600
For one the A600 is 16bit and the A1200 is 32bit, now this translates to how it deals and processes its data - as such it uses 2x 16bit ROM's as 32bit words (i.e. each data fetch is 32bits) - On the A600 its data fetch is 16 bits - the only exception to this is the CD32.
Its important to note that the ROM(s) in the A1200 is right aligned - thats to say that with the rear ports at the back the rom must be placed furthest right in the socket.
have a close look at this picture
Its imperative that the ROMs are align in such a fashion or they will be destroyed - if this happens even for a second, then you will need to replace the ROMs.