solved:
Hey, it’s solved:
One of the Expansion Boards is indeed broken: Something with the Power-Management isn’t working and the board is dead.
the other one worked after i resoldered the pin-slots. it’s working fine now.
the third one had no problems whatsoever.
i wonder if it’s just bad luck or if something happened with my delivery, cause the working one was packed in the starter-kit-case and the other ones were loose