The short answer
A Black+Decker microwave showing this usually tells you one thing: sparking, smells and trips are stop-now findings, and most of them are caused by something in the cavity rather than inside the case. Checking the load, the waveguide cover and the cavity is free and safe with the oven unplugged. Everything else here is a stop-using decision.
What you actually see
- Sparking or arcing inside the cavity — Visible sparks are a stop-now condition whatever caused them.
- A burning smell during or after a cycle — A smell means unplugging the oven immediately.
- Scorch marks on the cavity wall or the waveguide cover — Scorching marks where arcing has already happened.
- A mild tingle when touching the case — Any sensation from an appliance case means stopping and having the circuit checked.
Causes, ranked for this microwave
- Metal in the cavity — The usual answer. foil, a metal-trimmed dish, a twist tie or a fork is the most common cause of arcing by a wide margin, and it is entirely preventable. Rule it in or out properly here; a maybe at this position costs an hour further down.
- Waveguide cover damaged or dirty — The runner-up. it is the second most common cause and the most common one that leaves a visible mark. Getting a definite answer here is worth more than a quick look at the three below it.
- Food residue burnt onto the cavity wall — Third. carbonised food conducts, and a burnt-on patch becomes an arc point that grows every time the oven is used. If this is the answer, the rest of the list stops mattering entirely.
What to check, in order
- First — what was put in the oven — Repeat with a plain glass or ceramic dish. Arcing that stops is answered.
- Second — the small cover on the cavity wall — Look at the small panel on the cavity side wall. Grease, scorching or a hole in it is the finding.
Checks an owner can do safely
- Step 1. Test with water in a plain dish — Run a short cycle with a mug of water and a plain glass or ceramic dish, watching through the door for a spark.
Tools: mug, waterAbout 5 min
- Step 2. Inspect the cord, plug and socket — With the oven unplugged, run the cord through your hand and check the pins and the socket for heat discolouration.
Tools: noneAbout 10 min
- Step 3. Stop the oven and unplug it — At the first spark, smell or trip, stop the cycle and unplug the oven. Nothing else on this page happens with the oven live.
Tools: noneAbout 1 min
Before you open anything
Safety
Unplug it, and treat the inside as off limits. The high-voltage section of a microwave remains dangerous with the power disconnected. A damaged door, a bent latch or a failed switch is a reason to stop using the oven, never a reason to work around it.
When this becomes a service call
Stop and call when the next thing to do meets any of these. A burning smell, a scorched waveguide cover or a damaged door is a stop-now finding rather than a step in a diagnosis.
Sources
General guidance- The Control of Hazardous Energy (Lockout/Tagout) — OSHA 1910.147 and manufacturer service manuals, fetched
- Article 210 — Branch Circuits — NFPA 70 (National Electrical Code), fetched
Nearest pages
What this page does not cover
Treat what follows as the class-level answer for a Black+Decker microwave. It will not tell you which board your unit has, which part number fits it, or what a particular code means on a particular family, because those differ within the range. The family and model pages beneath this one carry that, and they are linked under Related pages.
Lead Appliance Repair Technician · 12 years experience
Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
