White countertop microwave on a kitchen counter
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Microwave runs but does not heat

No heat means the high-voltage circuit is not producing microwaves: HV fuse, HV diode, HV capacitor, magnetron, HV transformer, a door switch, or (on inverter models) the inverter board. Every internal test is high-voltage work for trained techs only, with the cord unplugged and the HV capacitor discharged and verified.

Cross-checked ~60 min advancedBrands: All

Before you start

  • DANGER: the high-voltage capacitor can hold a lethal charge even when the microwave is unplugged
  • Inexperienced users should NOT open the cabinet. Refer to a trained technician
  • Trained techs: unplug, wait, discharge the HV capacitor with an insulated discharge tool, and verify 0 V with a meter before touching any internal part
  • Never run the microwave with the cabinet off or with door interlocks bypassed

Diagnostic steps

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OnCall Tech is a reference tool for trained technicians and can make mistakes. Always disconnect power and confirm with the manufacturer's documentation before you work.

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