The short answer
Sparking inside a Black+Decker BDCM 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 BDCM models the check that decides the order below is which build you have: grease filters underneath, or not.
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 — 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.
- The plug or the cord is warm, or the outlet is discoloured — Do not keep using the socket.
- Lights dim elsewhere when it runs — A shared circuit carrying more than it comfortably can.
- NEAR MISS — arcing that stops when the foil comes out — 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 ranks first wherever the sparking stops when the offending item comes out. Check the cavity with the oven unplugged and good light.
- 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 is placed here because it explains tripping without any arcing, which the causes above do not.
- 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.
Check in this order, and why
- Take the oven out of service before diagnosing anything — Arcing, tripping and burning smells are all conditions to act on rather than to reproduce.
- Look for metal, foil or metallic trim — If the arcing goes with the metal, the oven is behaving correctly.
- Look for scorching on the small panel inside — 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.
When to call a technician
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 BDCM models
Lead Appliance Repair Technician · 12 years experience
Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
