Well, it looks like after many years, the mainboard of my very first A500 reappeared in my parents basement. 8-) I tried it out, but unfortunately it refuses to boot. The disk drive spins up, the start logo disappears for a second, but then it stops and the start logo is there again. The behavior is like when you insert a disk that is not bootable. I tried 2 different floppy drives that are known to work, already exchanged both CIAs, but no luck. Anything else I could check / exchange?