The answer, before the detail
Expect circuit overloaded or shared with other appliances first — and expect this page to be shorter on repairs than most, because the components that cause the remaining faults are behind a cabinet no owner should remove.
What the microwave is actually doing
- Sparks around a dish with a metallic trim — Metal in the cavity, and the dish rather than the oven is at fault.
- A buzzing or louder-than-usual hum with the sparking — A change in the oven's sound alongside arcing points at the internal high-voltage side.
- A burnt or scorched patch on the cover in the cavity wall — The waveguide cover has been arcing against grease or food, and it is the classic cause.
- NEAR MISS — no sparks, but the oven does not heat — An oven that runs cold without arcing is a heating fault, and that page covers it.
What actually causes this, ranked
- Circuit overloaded or shared with other appliances — Extension leads make it worse: a lead that is too light for the load heats up, and that is a genuine fire risk rather than an inconvenience. Number one here, because this is what the oven meets first and what owners notice last. Commercial equipment is specified for throughput, so the causes that rank high here are the ones throughput drives: loading, supply and cleaning routine.
- Cutlery left in a bowl — Metal in a microwave concentrates the field at its edges, and the result is a visible arc. A twist tie, a scrap of foil, the gold band on a plate or a fork left in a bowl are all enough, and all produce a dramatic display with nothing wrong with the oven. Second, because it produces the same complaint from the other side and is still an owner-side check.
- The small panel in the cavity wall scorched — There is a small removable cover on the cavity wall that protects the opening where the energy enters. It absorbs splatter, and once that splatter carbonises it starts to arc — which burns the cover further, which makes the arcing worse. It ranks here because it is genuinely less common, not because it matters less when it happens.
- The oven arcing with a clean, empty cavity — The capacitor in a microwave can hold a dangerous charge long after the oven is unplugged, which is why the outer cabinet must never be removed by an owner, however simple a video makes it look. Least likely of the four, and the one that only makes sense once the others are ruled out.
What to check first, second, third
- Note what else was running when the breaker tripped — A kettle and a microwave on the same circuit is the classic combination. First, because it separates the top two causes in under a minute.
- Stop the oven and look at what is inside for any metal at all — Rims, trims, ties, skewers and foil are the usual finds. Next: it confirms or clears the cause ranked second, and needs nothing but light.
- Look at the small cover on the cavity wall for burn marks or grease — A dark scorch mark there is the answer, and it tells you the arcing is not from your dish. Third in sequence — useful, but rarely where the answer turns out to be.
What you can do yourself
- Stop using the oven if the breaker trips with nothing else running — A breaker that trips on the oven alone is protecting something, and retrying is not a test.
About 5 min
- Check the dishes in regular use for metallic trim — Decorative gold and silver banding is the most commonly missed source.
About 10 min
- Stop using the oven if the cover is burnt through or charred — A charred cover will keep arcing and will damage the cavity behind it.
About 5 min
- STOP if a step would mean defeating an interlock or a safety switch — Those exist to stop the appliance running in a state that can hurt someone. There is no version of this job worth bypassing one.
Before you touch anything
Safety
Unplug the oven before cleaning anything inside it, and never remove the outer cabinet — the capacitor in a microwave can hold a charge capable of killing long after the oven is unplugged, and that is true of every model. Never run the oven empty, and never operate it with a damaged door.
When to stop and call
The owner side of this page ends at the cavity. Cleaning, checking for metal and moving the oven to its own socket are all yours; anything behind the panel is not, and on most ovens a high-voltage repair costs more than the appliance.
Pages next to this one
What is not on this page
This is the generalized page for Koolmore microwaves. If a page exists for your particular family or model line, it is linked from this section and it outranks this one for your unit. What is deliberately absent: part numbers, connector pinouts and the service-manual sequences, which are family-specific and wrong the moment they are generalized.
Lead Appliance Repair Technician · 12 years experience
Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
