White countertop microwave on a kitchen counter

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Field pattern: microwave dead after a pop (blown line fuse: door switches and HV parts, discharge first)

A blown line fuse is a symptom. Techs most often find a failed door monitor switch or worn latch parts (the monitor switch deliberately shorts the line if the interlocks fail), or a shorted part in the high-voltage section. The wrong turn is replacing the fuse alone, or replacing switches without checking the latch and the HV capacitor, diode and transformer.

Cross-checked ~60 min advancedBrands: All

Before you start

Unplug the microwave before opening the cabinet; the high-voltage capacitor can hold a lethal charge after unplugging
Discharge the HV capacitor before touching anything in the HV section, and verify it is discharged
Never operate the microwave with the cabinet open; never measure HV live
Do not defeat or jumper door interlocks; replace switches with the exact type

Diagnostic steps

Unlock all 8 steps with expected values

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