@yaqube: Sorry, ma english is not too good, I got you wrong. Now I understand: No, when I place only the original Chip and NO other ROM-Chip on the Kickstart-switch the Amiga does not boot. The same for the 27C400.
What do you mean with pullup-resistor? Could I solder an resistor to the 27C400 to help solving the problem?
@mfilos: I tried it with an "AMD 27C400-105" a few minutes ago; the same Problem: permanent re-boot. But as I reported: Placing the EPROM on the Kickstart-Switch makes it run.