Why Is My Microwave Sparking Inside? (Magnetron & Waveguide Guide)

Understanding Microwave Arcing

Seeing sparks inside a running microwave is terrifying. This phenomenon is called "arcing" and is caused by microwaves reflecting off metal surfaces, creating electrical sparks. However, it often happens even when there is no metal foil inside.

The Burnt Waveguide Cover

On the inside wall of your microwave, there is a small cardboard-like sheet called the waveguide cover. It protects the magnetron (which generates the heat) from food splatters. If grease splatters on the cover, the grease absorbs microwave energy, superheats, and burns, turning into carbon. Carbon conducts electricity, creating a short circuit that sparks aggressively.

Damaged Magnetron Cap

If a burnt waveguide cover is ignored, the sparks will damage the metal antenna cap of the magnetron. Once the magnetron cap is pitted or melted, the microwave won't heat food, and the magnetron itself will require replacement.

A Quick and Cheap Fix

If caught early, replacing a burnt waveguide cover is extremely inexpensive. Our technicians clean the carbon track, install a new mica sheet, and test the magnetron output. Never operate a sparking microwave, as it can burn out the main board.