DifficultyEasy

Time15–30 minutes

What you saveWaveguide cover $5–$20 DIY vs $80–$250 professionally

⚠️ BEFORE YOU START

STOP USING THE MICROWAVE UNTIL THIS IS FIXED. Unplug it before you start. Never remove the outer metal cabinet of a microwave. The high-voltage capacitor inside stores a charge that can kill you, and it holds that charge after the unit is unplugged. Every step in this guide stays outside the cabinet or inside the cooking cavity — if a repair needs the case off, it is a job for a technician. Everything in this guide happens inside the cooking cavity, where it is safe to work.

Tools

Scissors or craft knife
Small screwdriver
Soft cloth
Mild detergent

Parts

Mica waveguide cover sheet (universal or model-specific)

Step by step

1 Unplug the microwave and let it cool

Pull the plug from the wall — not just the switch. Give it a few minutes if it has been running.
2 Look for metal in the cavity first

Foil, a twist tie, a metal-rimmed plate, or a metal rack touching the wall will all arc. If you find any, that was almost certainly your problem — remove it and test again before buying anything.
3 Find the waveguide cover

It is the thin, slightly rough panel on the right-hand wall or the roof of the cavity, usually beige or grey and roughly the size of a playing card. Look for scorch marks, holes, or a charred, blistered patch.
4 Clean the cavity thoroughly

Carbonised food residue conducts and arcs all on its own. Wipe every surface with mild detergent and a soft cloth, and pay attention to the roof, which people rarely clean.
5 Remove the damaged cover

It is held by one or two small screws, or by tabs that slide out of a slot. Note which way round it sits and photograph it before removing it.
6 Cut the replacement to match

Universal mica sheet cuts with scissors or a craft knife. Lay the old cover on the new sheet, trace it, cut slightly outside the line, and transfer the screw holes.
7 Fit the new cover and test

Screw or slide it into place, plug the unit back in, and heat a cup of water for one minute. No sparks and hot water means you are done.

🔧 Hand-off point: If it still arcs with a fresh cover and a clean cavity, stop there. That points behind the cover — into the waveguide or the magnetron antenna — and that is inside-the-cabinet work nobody should attempt at home. find a microwave repair pro near you →

🔧 WHEN TO CALL A PRO

If the arcing continues with a new cover and a spotless cavity, stop. That points at the magnetron antenna or damage inside the waveguide itself, and that is inside-the-cabinet work. Continuing to run a microwave that arcs risks damaging the magnetron and, in the worst case, a fire. If you'd rather skip it entirely, find a microwave repair pro near you →

Sources

Where the safety, regulatory and warranty claims on this page come from. Repair costs are our own figures based on Arizona market rates and OEM parts pricing.

Microwave Ovens — Radiation-Emitting Products U.S. Food & Drug Administration The federal requirement for two independent door interlocks plus a monitoring system, and the 21 CFR 1030.10 leakage limit — why an interlock must never be bypassed.