The short answer
Sparking inside a Black+Decker AM microwave, a breaker that trips when it starts, or a burning smell are all stop-now conditions rather than diagnostic puzzles. Unplug the oven first and read the rest afterwards. On these models the commonest innocent explanation is metal in the cavity or a worn waveguide cover, and both are checked in a minute with the oven unplugged — but the cabinet is never opened, on any model. Settle the build before the ranking applies: these models divide on a glass turntable.
What you observe on these models
- The breaker trips when the oven starts — Note whether anything else is running on the same circuit.
- Visible arcing while it runs — Stop it immediately. Metal in the cavity or a damaged waveguide cover are the two usual explanations.
- A burning or electrical smell — Unplug it. A smell like this is not something to reproduce for diagnosis.
- The plug or the cord is warm, or the outlet is discoloured — Do not keep using the socket.
- The circuit visibly struggles with it — A standard household branch circuit is 15 A or 20 A at 120 V, and a microwave asks for a large share of one.
- NEAR MISS — sparks only with a dish with metal trim — That is the oven behaving correctly around metal it was never meant to heat.
Causes, ranked for the AM build
- The waveguide cover is soiled, burnt or damaged — This takes the top spot once metal has been ruled out: the cover is a consumable that chars where food splashes on it and arcs where it has burnt through. Arcing from one spot repeatedly is the signature.
- The circuit is shared, or the outlet and cord are damaged — It rises where the oven shares a kitchen circuit with other large appliances.
- Metal in the cavity — foil, trim, a twist tie or a skewer — It is placed here because it costs little to rule out and rules out more than it costs.
- Grease-loaded filters or a blocked vent on an over-the-range machine — It is ranked here because it explains a hot smell with no arcing at all.
- A high-voltage component, the magnetron or the diode — It comes last as the diagnosis of exclusion: tripping with nothing in the cavity, clean cover, sound outlet.
The order that finds it fastest
- Take the oven out of service before diagnosing anything — Everything below is done with the plug out.
- Look for metal, foil or metallic trim — Gold and silver decoration on crockery arcs exactly like foil.
- Inspect the waveguide cover on the cavity wall — Char marks or a burnt-through patch explain repeated arcing from one spot.
- Feel the plug and look at the socket — A microwave asks a lot of a shared kitchen circuit at start.
Power off first
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 AM models
Lead Appliance Repair Technician · 12 years experience
Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
