The short answer
Tripping, heat at the plug, sparks or a burning smell on a B machine are the one class of fault where the first step is to stop rather than to diagnose. A countertop machine is plugged into whatever socket is free, which is where most of these faults begin.
What you observe on these models
- The breaker trips when the machine starts heating — A supply pattern: the load is finding the limit of the circuit.
- A burning or fishy smell during or after use — Overheating insulation somewhere.
- Flashes only when a particular dish is used — Metal trim on that dish, not a fault in the machine.
- A crackling sound with an empty cavity — That points at the cover or at charred residue, and it ends the owner part of the job.
- NEAR MISS — a hum that has always been there — A microwave is a noisy appliance, and an unchanged noise is not an electrical fault.
Causes, most likely first on the B family
- A blown internal fuse from a door-switch failure — First on this platform: this presents as a machine that trips the breaker or dies instantly on closing the door, and it means a switch has failed out of sequence.
- A shared circuit carrying more than it can — Second: a microwave draws heavily and briefly, which is exactly the load that finds a marginal circuit.
- Arcing inside the cavity — Third: foil, a metal-trimmed dish, a twist tie or a damaged waveguide cover all produce flashes and a sharp crackle.
- An extension lead or a multi-way adaptor — Fourth: this appliance draws heavily and briefly, which is exactly the load an adaptor is least able to carry.
- Metal in the cavity — Last: foil, a metal-trimmed plate, a twist tie or a thermometer will flash and crackle.
Check in this order, and why that order
- Unplug the machine and feel the plug and the socket — Warm plug with a cool cord means poor contact at the socket, and that is a fire risk rather than an inconvenience.
- Note exactly when the breaker trips — On starting is a supply problem; on closing the door is a switch and fuse problem; at random is neither.
- Run the machine alone on its circuit with everything else switched off — It separates an overloaded circuit from a faulty appliance in one test.
- Look inside for burn marks and check the waveguide cover — A cover burned through no longer protects what is behind it.
- Stop and call for any burning smell, any smoke or any visible damage — Unplug it and leave it unplugged.
Before you open anything
Safety
Unplug the appliance or switch off its breaker before removing any panel. A capacitor can hold a charge after the power is off. Treat that as the first step of every check below that involves a panel, a grille or a cover.
Models in the B family — The numbers this page covers.
Reference| Model number | Family key |
|---|---|
| B20PXP78 | avanti:microwave:b |
When to call a technician
Proving a socket, moving the machine to a circuit of its own and keeping metal out of the cavity are owner work. On these models the line falls at the outer case, and everything behind it. Call without working through anything at all for a socket or plug that heats under load, which is a fire risk rather than a nuisance.
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