The short answer
A Black+Decker EM microwave that trips, arcs or smells hot has told you enough to act on. Switch it off and unplug it before anything else. What can then be checked from outside is short: what was in the cavity, the state of the waveguide cover, the outlet it plugs into, and on an over-the-range machine the grease filters. Everything else is a service call. Settle the build before the ranking applies: these models divide on grease filters underneath.
What the owner actually sees
- The breaker trips when the oven starts — Note whether anything else is running on the same circuit.
- Sparks or flashes inside the cavity — Stop it immediately. Metal in the cavity or a damaged waveguide cover are the two usual explanations.
- A hot smell that lingers after it stops — On an over-the-range machine, check whether the filters are loaded with grease.
- Heat at the wall rather than at the oven — Do not keep using the socket.
- The circuit visibly struggles with it — A shared circuit carrying more than it comfortably can.
- NEAR MISS — arcing that stops when the foil comes out — Remove the metal; if the arcing goes with it, there is nothing further wrong.
Most likely first on this family
- Metal in the cavity — foil, trim, a twist tie or a skewer — It leads because it is the commonest explanation for arcing by a wide margin and because it is not a fault at all. Gold or silver trim on a dish arcs exactly like foil does.
- The waveguide cover is soiled, burnt or damaged — It ranks high because it is the one internal-looking part that is owner-replaceable from inside the cavity, without opening the cabinet.
- Grease-loaded filters or a blocked vent on an over-the-range machine — Mid-list, and specific to machines mounted above a range: the filters and the fan path above a hob collect grease that then cooks.
- The circuit is shared, or the outlet and cord are damaged — It rises where the oven shares a kitchen circuit with other large appliances.
- A high-voltage component, the magnetron or the diode — Last of these, and not because it is rare — because it is the one thing on this list nobody but a technician may look at.
Check in this order, and why
- Stop the oven and unplug it — Arcing, tripping and burning smells are all conditions to act on rather than to reproduce.
- Check what was in the cavity — If the arcing goes with the metal, the oven is behaving correctly.
- Inspect the waveguide cover on the cavity wall — Char marks or a burnt-through patch explain repeated arcing from one spot.
- Check the outlet, the plug and what shares the circuit — A microwave asks a lot of a shared kitchen circuit at start.
Before you open anything
Safety
The cabinet stays closed — on every model, for every fault. A microwave oven holds a high-voltage capacitor that can carry a lethal charge after the plug is out, so the only safe work is on the outside: the door surfaces, the turntable, the filters where they are fitted and the outlet it plugs into. Unplug it before touching any of that.
Where the owner job ends
The condition is whether the cause is in the cavity or behind it. Metal, a charred waveguide cover and greasy filters are all in the cavity or on the outside, and all of them are yours. Anything else — a magnetron, a diode, a capacitor, the wiring behind the panel — is a technician job on an oven that stays unplugged until they arrive.
Other faults covered for the EM models
Lead Appliance Repair Technician · 12 years experience
Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
