The short answer
A flash, a smell or a tripped breaker on a Nexel microwave is most often a charred or soaked waveguide cover, and the majority of these have a cause you can see without opening anything. This is a commercial machine, built for a duty cycle a household unit never sees, and that is what sets the order below. These sit on a stainless bench in a working kitchen, surrounded by steam, grease and everything else that a service line throws at them.
What you observe
- Flashes, crackling or a bang from inside the cavity — Arcing, and it usually has a visible cause.
- A burnt smell that is not the food — Hot varnish and scorched plastic smell quite unlike burnt food.
- The breaker trips the moment heating starts — Timing points either at the circuit or at the high-voltage section.
- A hot plug or a discoloured socket — This one is about the wiring rather than the appliance.
- NEAR MISS — the smell is food burnt onto the cavity floor — That is cleaning rather than a fault, and it clears with the residue.
Causes, most likely first on this platform
- A charred or soaked waveguide cover — Ranked second on a box used hard: the small panel on the cavity wall absorbs splatter, carbonises, and then arcs against itself every time the oven runs. On a service line the box is surrounded by steam and airborne grease all day, which is what moves this up the list.
- Arcing inside the cavity — First, because it is what people actually see: a flash, a crackle and a burnt smell.
- A hot plug, a scorched socket or a warm lead — This one is not about the oven: a microwave draws hard, and a loose socket or an undersized extension lead heats at the connection.
- A breaker that trips when the oven fires — A trip exactly when heating starts points either at a shared circuit that is simply loaded, or at a failing component in the high-voltage section.
Check in this order, and why
- First: inspect the small cover panel on the cavity wall — Second because a charred cover arcs at the same place every time and the damage spreads until it is replaced. In a working kitchen the grease gets everywhere first, so this is where to look first.
- Second: look for metal, foil or a burnt spot before running it again — First because the most common cause of arcing is something that was put in the oven, not the oven itself.
- Third: feel the plug and look at the socket after a few minutes of use — A hot plug is a wiring fault, and it is checked early because it is the one that can cause a fire.
What an owner can safely check
- Inspect the small cover panel on the cavity wall — A charred cover arcs at the same place every time and the damage spreads until it is replaced.
Tools: flashlightAbout 5 min
- Stop, unplug, and look inside for metal or a burnt spot — Most arcing has a cause that is sitting in the cavity. Find it before running the oven again.
Tools: flashlightAbout 10 min
- Feel the plug and look at the socket after a few minutes of use — A hot plug or a discoloured socket is a wiring fault, and it is the one on this list that can start a fire.
About 10 min
- STOP HERE — the high-voltage section is never an owner check — Unplugging does not make it safe: the capacitor holds a charge that can kill. If the fault is inside, the oven goes to a technician or it goes away.
Before you open anything
Safety
Never open the cabinet of a microwave oven. Unplugging it does not make it safe: the capacitor in the high-voltage section stores a charge capable of killing long after the power is off, and there is no owner check behind that panel at any level of skill. Never defeat or tape a door interlock, never run the oven empty, and stop using it immediately if the door, the inner panel or the perforated screen is damaged.
When to call a technician
Call, and stop using the oven, for any of these: a burning smell that returns with no food in the cavity, a breaker that trips when heating starts, scorching at the plug or socket, or arcing that continues after the cavity is clean and the cover panel replaced. Anything involving the high-voltage section is a technician's job by definition.
Nearest pages of this class
What this page does not cover
Read this as the class-level answer. It stops short of anything that changes model to model — connector pinouts, electrical test values, the sequence for pulling a panel and all part numbers — because getting those wrong is expensive. A family or model page, where one exists, is linked among the siblings and takes precedence over this page.
Lead Appliance Repair Technician · 12 years experience
Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
