The short answer
Sparking inside a Black+Decker BMG 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. What separates BMG units here is visible without a tool: a touch panel rather than a dial, or nothing of the sort on the other build.
What the owner actually sees
- Visible arcing while it runs — Never run it again to see whether it does it twice.
- 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.
- 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 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. 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. A standard household branch circuit is 15 A or 20 A at 120 V, and a microwave takes a large share of one at start.
- 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. A visit is the only next step.
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.
- 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.
- 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
Never open the cabinet of a microwave oven. The high-voltage capacitor inside can hold a lethal charge long after the machine is unplugged, and nothing behind that cover is an owner part on any model. Unplug the oven before cleaning anything, leave every door interlock exactly as it is, and do not run the oven empty. If the door is damaged, if it has been dropped, or if the oven runs with the door open even for a moment, stop using it and unplug it.
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. Until the visit, keep it unplugged: this is one of the few appliance faults where continuing to use it is the actual risk.
Other faults covered for the BMG models
Lead Appliance Repair Technician · 12 years experience
Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
