3.5 Hours - and it works. Many thanks to the author. Without these instructions it is impossible. While reassembling, the clicwheel cable didn't slip in well, then I removed the logic board again, but the battery already was sticked to the case an tore out the metal frame of the logic board and killed the cable to the speaker connector. But I can live without it.

It was a real challenge, but also fun to be able to repair a device that was not designed to be repairable.