The short answer
When the BMO family sparks, smells hot or trips its breaker, the appliance is telling you something that does not need interpreting. On these models the safe sequence is short: unplug it, do not open it, and have it assessed before it is used again.
What you actually observe
- Visible arcing or sparking inside the cavity — Metal, foil, a damaged waveguide cover or food residue. Stop the cycle immediately and unplug the appliance.
- A burning or electrical smell during or after a cycle — Something is overheating inside the case. It does not clear by itself and it does not get better.
- The circuit breaker trips when the appliance runs — A shorted component, or the interlock monitor switch doing its designed job. Either way the appliance stops being used.
- NEAR MISS — a loud hum with no heat and no smell — That is the no-heat page. It still needs a technician, but it is not the same urgency as arcing.
Causes, most likely first on the BMO family
- Metal, foil or a metallic trim in the cavity — First on these models and the only cause an owner can correct, by not doing it again. Metal reflects energy into an arc, and the arc damages whatever it strikes. The family spans more than one cavity size, and the larger cavities carry a heavier door — that lifts the latch and interlock causes up this list.
- Waveguide cover charred, damp or perforated — Second. That small panel protects the opening where energy enters the cavity, and once food residue has charred on it, it arcs on every cycle until it is replaced.
- Food residue or moisture on the cavity wall or door edge — Third. Residue absorbs energy, carbonises, and then behaves like a conductor — which is how a clean-looking appliance starts sparking.
- High-voltage component failing — diode, capacitor or transformer — Fourth. It produces the burning smell and the breaker trip rather than visible arcing, and it is strictly technician territory.
- Interlock monitor switch shorting deliberately — Last, and by design: when the door interlocks fall out of sequence this switch blows the internal fuse, which can trip the household breaker too.
Check in this order, and why
- Stop the cycle and unplug the appliance — This is a step rather than a precaution. Nothing else on this page happens until the appliance is isolated.
- Look for metal in the cavity — foil, a trim, a twist tie, a metal-rimmed dish — It is the commonest cause of visible arcing and the only one with an owner-side answer.
- Stop and book the repair — do not open the case — Last, and absolute: the capacitor inside holds a lethal charge after the appliance is unplugged.
Before you open anything
Safety
Unplug the microwave immediately at the first sign of arcing, burning or a tripping breaker, and do not remove the outer case under any circumstances — the high-voltage capacitor inside holds a charge capable of killing after the appliance is disconnected. Never run the appliance empty, never run it with metal inside, and never use it again after a burning smell until it has been assessed. If there is smoke, isolate the circuit at the breaker rather than reaching behind a hot appliance.
Models in the BMO family
Reference| Model number | Family key |
|---|---|
| BMO650SIL/A | breville:microwave:bmo |
| BMO850BSS/A | breville:microwave:bmo |
| BMO870BSS/A | breville:microwave:bmo |
When to call a technician
Call for any burning smell, any breaker trip, and any arcing that continues after the cavity and waveguide cover have been cleaned and checked for metal. Call rather than experiment if the appliance has burn marks on the cavity wall or the door edge, because those surfaces are part of the containment. The only outcomes an owner should reach on this page are "there was foil in it" and "the cavity needed cleaning"; anything else is a technician visit.
Other faults covered for the BMO family
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.
