What this usually is
The usual answer on this unit is metal or foil in the cavity, or a burnt waveguide cover, with a failing magnetron, diode or transformer next. The difference between them matters to a technician and not to you: the oven comes out of service either way. Everything an owner can safely do here is outside the cabinet: the socket, the cord and the cavity.
The symptoms, and their near misses
- The breaker trips when the oven starts — A short or a heavy fault current at the moment the load comes on.
- NEAR MISS: the oven will not start at all and nothing smells — Read the page on a microwave that will not start instead.
The ranking: most likely cause first
- Metal or foil in the cavity, or a burnt waveguide cover — Foil, a metal trim on a dish, or a food-soiled waveguide cover arcs and burns. The cover is the small board-like panel in the cavity wall, and once it chars it arcs every time the oven runs. First, and the whole order below follows from it: it is the only cause on this page that an owner can see, and it is the one that most often turns a clean oven into a burning one.
- A failing magnetron, diode or transformer — The high-voltage components fail under load, with a sharp electrical smell, a loud buzz, or a breaker that trips the moment the oven starts. Second: it is the cause that produces the burning smell people describe, and it is the point where the answer stops being a check and becomes a decision about the oven.
- The high-voltage capacitor, which is why the cabinet stays shut — The capacitor holds a lethal charge after the oven is unplugged and it does not discharge on its own. Last, and that is the point of this order: it is not a fault at all: it is the constraint that governs every other cause above it.
What to check first, second, third
- Look at the cavity wall panel for charring or holes — A burnt cover arcs on every use and gets worse each time.
- Note whether the smell or the trip happens the instant the oven starts — That timing points inside the cabinet, where an owner does not go.
- There is no owner check inside the cabinet, at any point, for any fault on this page — That is the whole of it.
The checks you can make yourself
- With the oven unplugged, look for a charred or holed panel on the cavity wall, and check nothing metal is being used inside — Do not run the oven again with a charred cover.
Tools: a torchAbout 10 min
- STOP AT THIS POINT: the cabinet stays shut whatever the fault — The high-voltage capacitor holds a lethal charge after unplugging. Call a technician or replace the oven.
Safety first, and it is not boilerplate
Safety
Unplug the microwave now and leave it unplugged. The high-voltage capacitor inside holds a lethal charge after the power is off and does not discharge on its own, so never remove the cabinet for any reason. Never run the oven empty, never run it with a charred waveguide cover, and never defeat a door interlock. A standard household branch circuit is fifteen or twenty amps at one hundred and twenty volts, so an oven that trips its breaker is reporting something real.
When to call a technician
Call, or replace the oven, if it arcs, smells of burning electrics, trips a breaker, or buzzes far louder than it used to. Have an electrician look at a plug or socket that is discoloured or warm, because that fault is in the wiring rather than the appliance.
Where to go next in this class
What this page does not cover
This page covers the Whirlpool Corporation microwave as a class, not one family or model line. Where a family- or model-specific page exists it is linked here. Deliberately not here: component part numbers, capacitor discharge procedures, high-voltage test methods and any cabinet removal sequence, none of which belong in a home guide.
Links: - [A Whirlpool Corporation microwave that will not begin a cycle](/blog/whirlpool-corporation-microwave-wont-start) - [Why a Whirlpool Corporation microwave door will not seal properly](/blog/whirlpool-corporation-microwave-door-seal) - [A Walmart Hamilton Beach microwave that arcs, smells or trips its circuit](/blog/walmart-hamiulton-beach-microwave-electrical-safety)
Lead Appliance Repair Technician · 12 years experience
Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
