thanks for the responses.
There is an English description with individual times in the comments for the video.
Vibration test: ok, maybe it will be added in the future.
disconnecting ground power: I tried it again. it has to be disconnected BEFORE starting the APU. That works. But if I want to disconnect after turning on the APU, it doesn't work. I tried disconnecting after starting the engines and that didn't work either. According to the video tutorial from Raffi75, it works the same for me.