Check inside please:

https://www.tophomeapps.com/ge-microwave-fuse-keeps-blowing/

Door Switch Problem

A door switch  probably has a problem when a fuse breaks while the door is being opened or closed.

Microwave ovens often contain three or four door switches that are intended to trip a fuse and turn off power to the microwave if the door is not closed correctly.

Usually, a door switch will stop working because of wear and tear or because it is jammed. The wrong door switches being placed might potentially blow a fuse.

 

Using a multimeter, door switches may be checked for continuity (a continuous electrical route) to see whether they need to be changed.

Before using the microwave, be sure to heed the safety advice above.

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This switch is controlled by the door. When the door is open, this switch is closed (NC, normal closed). When the door is closed, where the button is pushed, this switch should be open.

But the broken switch does not fuction. Either the door open or closed, the switch remains closed. When the button is pushed (the door is closed), it remains closed. 

So I think, this closed switch probably makes a short circuit when the ON button on the display panel is pushed (while the door is closed), the fuse/breaker in the basement keeps blown.

The new switch restore the original circuit, when the door is closed, it makes no short circuit, so the fuse/breaker will not be blown.