The answer first
Stop using the oven and unplug it first; then read the list. On this machine the most likely cause is waveguide cover burnt or carbonised.
What you observe
- Sparks or a flash inside the cavity during a cycle — Arcing.
- A scorched patch on the waveguide cover at the side wall — Carbonised food on the cover, which then arcs against itself.
- A rust spot or chipped paint inside the cavity — Bare metal in a cavity arcs, and the oven should not be run.
- The breaker trips as soon as the cycle starts — A supply-side fault or a shorted component; neither is a cavity problem.
- NEAR MISS — it runs quietly and simply does not heat — That is a heating failure without an electrical fault, and it has its own page.
Causes, most likely first on a Sharp microwave
- Waveguide cover burnt or carbonised — The arcing then burns the cover further, so it gets worse with every cycle. Ranked first on a Sharp microwave: a carbonised cover arcs against itself, which is why this fault always worsens rather than settles.
- Metal, foil or a metal-trimmed dish in the cavity — Foil, a twist tie, a metal-rimmed plate or a fork will arc immediately and can burn the cavity wall.
- Chipped cavity paint or a rust spot — The cavity coating is what keeps the steel from arcing, and a chip or a rust bloom exposes bare metal.
- High-voltage component failure — None of it is owner-serviceable, and an oven behaving this way should not be run again.
Check in this order, and why
- Look at the small panel on the cavity side wall for scorching or holes — Never run the oven with the cover missing or damaged.
- Look at what was in the oven when it sparked — Check the plate as well: some decorative glazes contain metal.
- Shine a torch around the cavity, especially the corners and the base — Touch-up paint is not an owner repair on a microwave cavity.
What an owner can safely check
- Unplug the oven and inspect the waveguide cover; wipe light splatter off it gently — A cover that is scorched, holed or soft is a replacement part — never run the oven without it.
Tools: soft cloth, torchAbout 15 min
- Unplug the oven, remove everything from the cavity, and check the dish and any wrapping for metal — Foil, twist ties and metal-trimmed plates all arc. Remove them and inspect the cavity wall for burn marks.
About 10 min
- STOP HERE — the outer cabinet stays on — Everything past the cavity and the door is high-voltage work, and it is not an owner job at any point.
Before you open anything
Safety
Pull the plug before any check, and leave the outer cabinet where it is. The capacitor inside can hold a lethal charge after the power is off, which is why this is the one kitchen appliance with no owner-side internal work at all. The door interlocks must never be taped, bent or bypassed. Do not run the oven empty, and take it out of service if the door is damaged, sagging or will not latch.
When to call a technician
The line is the cavity: what you can see and remove is yours, and everything behind the wall is high-voltage work. A microwave that buzzes loudly, smells hot or trips a breaker stays unplugged until a technician has seen it. Sharp parts are generally obtainable through appliance parts distributors, which makes a repair worth pricing rather than writing off.
Nearest pages of this class
What this page does not cover
This page covers the Sharp microwave as a class, not one family or model line. Where a family- or model-specific page exists for your unit it is linked above and it is the better answer — read it first. Deliberately not here: part numbers, wiring colours, panel removal order and torque figures, all of which differ between families under one nameplate.
Lead Appliance Repair Technician · 12 years experience
Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
