One more question i forgot:
Is the burned upper Mosfet the reason why i have a short circuit when i plug the PCB to 12 V? There are sometihing like 50 Ohm between the measure points , so its completly far away from infinite and definitly damaged, but is this the reason why the power source goes instantly down? Or maybe there are more burned parts ?
Yes it's definitely the reason for the power supply going off I had the same happen to my blade, replace the upper mosfet with CSD16321Q5
Also be carefully to not pull the mosfet off, let the hot air station reach temperature for a while, then apply heat to the left of it, it should be able to slide right off, do not pull it, if the solder is not molten it will pull the tracks from the board and cause damage. ;-)