The answer, before the detail
Sparking inside a Black+Decker AG 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. On the AG models the check that decides the order below is which build you have: a glass turntable, or not.
What the owner actually sees
- It runs for a moment then takes the circuit out — Note whether anything else is running on the same circuit.
- Sparks or flashes inside the cavity — Never run it again to see whether it does it twice.
- A burning or electrical smell — On an over-the-range machine, check whether the filters are loaded with grease.
- Heat at the wall rather than at the oven — That is the outlet or the connection rather than the oven, and it needs an electrician.
- Lights dim elsewhere when it runs — 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.
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.
- The circuit is shared, or the outlet and cord are damaged — It rises where the oven shares a kitchen circuit with other large appliances.
- 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.
- 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
- Stop the oven and unplug it — Everything below is done with the plug out.
- Check what was in the cavity — Gold and silver decoration on crockery arcs exactly like foil.
- Look for scorching on the small panel inside — 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.
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
Call once metal, the waveguide cover and the outlet have been ruled out and the oven still trips, arcs or smells hot. That leaves the high-voltage side, and the cabinet is never opened by an owner because the capacitor inside can hold a lethal charge after the plug is out.
Other faults covered for the AG models
Lead Appliance Repair Technician · 12 years experience
Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
