I have a neff H5642 built in microwave to look at. The customer decided to “Cook” nothing for 10 mins i.e. it was empty! 😳
The symptoms now are, when you select microwave and start. The oven starts up and then cuts out after a few seconds I guess about five to ten seconds. 8)
Tha magnatron doesn’t sound like it is firing up before the oven cuts out.