This will happen when the microwave starts a heating cycle. Leave the power cable plugged in but turned OFF to maintain a connection to earth.
Microwave Oven High-voltage Diode Set CL01-12 & HV-6X2P1 (Fuse blows on start)
Microwave Oven Diode Set 2X062H/HV-6X2P1 & HVM12/CL01-12 (Fuse blows on start)
Microwave Oven Diode CL01-12 and High Voltage Fuse 5kV 700 mA 0.70 A (No heat)
Microwave Oven Diode CL01-12 and High Voltage Fuse 5kV 800 mA 0.80 A (No heat)
Microwave Oven Diode CL01-12 and High Voltage Fuse 5kV 650mA 0.65A (No heat)
Microwave Oven High Voltage Capacitor with Fuse & Diode