Comment by MarkusWandel

Ironically the switches are cheap (from Ali Express anyway) and easy to replace and TMK virtually all microwaves use the same type. But yes, when you open the door, they do the following, in order:

- open to send a "stop microwaving" signal to the controller

- open to physically open the power circuit to the magnetron transformer

- close to short out the power after the above relay (the crowbar part)

The bottom two relays (in the list, not necessarily physical order) are independent of what the control board does. If due to mechanical slop, the bottom one switches before the middle one, boom goes the fuse. Even if you're just opening the door of an idle microwave. That's why, at least in mine, it says on a label inside, if the fuse is blown, replace the door switches along with the fuse.

The sequencing is very tight. You have to push the button veeerrry slooowly to actually observe the switches clicking in sequence.