Microwave Sparking Inside

• Metal in the cavity — Foil, a twist tie, a metal utensil or a dish with metallic trim or a gold rim can arc as soon as the microwave starts.
• Damaged or greasy waveguide cover — The small panel on an inside wall or the ceiling covers the opening where the energy enters and keeps food out of it, and once it is soaked with grease or charred it sparks and burns. Dried spatter on the walls or ceiling can char and spark the same way.
• Metal rack out of place — On models supplied with a metal rack, the rack can spark when it sits off its supports, touches a wall or is used in a mode the use and care manual rules out.
• Chipped or peeling cavity coating — Where the paint or enamel inside has chipped or rusted, bare metal edges can arc, and the spot grows if it is left. Stop using a microwave whose cavity wall has rusted through.
• Failing magnetron — A damaged magnetron antenna can arc behind the waveguide cover, which looks like flashes from the wall with nothing metal inside.
• Running it empty — With nothing inside to absorb it, the microwave energy reflects back toward the magnetron and can cause arcing and damage.

• Flashes from one spot on a side wall — The waveguide cover, or grease built up on it.
• Sparks around a dish rim or a utensil — Metal in the cavity, such as gold trim or a forgotten fork.
• Crackling with a burning smell — Charred grease or a burnt waveguide cover.
• Sparks from behind the waveguide cover with nothing metal inside, and a loud buzz — A failing magnetron, so stop using it until it is checked.
• Scorched spots on the walls or cover — A spot that has arced before and is likely to arc again until the cause is fixed.
• Flashes, popping or smoke from the vents or the outer cabinet — Arcing in the high-voltage parts or wiring, so switch it off at the plug or the breaker and leave the cabinet closed.

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