The short answer
A Criterion microwave that sparks, smells or trips its breaker should be stopped and unplugged before anything else, because arcing damages the oven every second it continues. On this class the usual cause is metal, foil or metallic trim in the cavity, with a damaged or soiled waveguide cover inside the cavity next to rule out, and both are assessed without opening anything.
What you actually observe
- Sparks that started with one particular plate or wrapper — The variable that changed is usually what was put in.
- Scorch marks on the cavity wall or its small cover — Visible damage that has already happened.
- NEAR MISS: food heats unevenly with no smell or spark — That is a heating performance question rather than a safety one.
The causes, most likely first on this brand
- Metal, foil or metallic trim in the cavity — Foil, a twist tie, a fork or a plate with a metallic rim all throw sparks in a microwave, and the damage from a few seconds of that can be permanent. Ranked first on a Criterion unit: a countertop oven is used for everything from reheating to defrosting, so foil, twist ties and metal-rimmed plates reach it far more often than they reach a built-in.
- A damaged or soiled waveguide cover inside the cavity — The small panel on the cavity wall shields the opening where the energy enters, and one that has burnt, blistered or soaked up food arcs and scorches on every use. Ranked second here: the cover on these ovens is a simple card-like panel that soaks up splashes and then arcs.
- A damaged cord, plug or socket — Ranked third here: a countertop oven is moved and re-plugged repeatedly and its cord takes the wear.
- A breaker or protective device tripping when the oven runs — Ranked fourth here: last, though a countertop oven on a busy kitchen circuit does trip it.
Check in this order, and why this order
- Look at what was in the oven when the sparking happened — A metallic rim on a favourite plate is the version of this that catches people out.
- Look at the small panel on the side or roof of the cavity for scorch marks — Brown marks or a blistered surface there is the commonest cause of arcing inside a microwave.
- Run a hand along the cord and feel the plug after a few minutes of use — A plug that is warm to the touch, or a cord with a flattened section, is the finding.
What an owner can safely check
- Take everything metallic out, including twist ties and decorative trim, and try again with a plain mug of water — A clean cavity with plain crockery is the control test.
Tools: mugAbout 10 min
- Stop using the oven and have the cover assessed rather than running it again — A scorched cover arcs worse each time and can take the cavity wall with it.
About 5 min
- STOP HERE if the next step needs a meter on live terminals or a panel off — That is where an owner check ends and a service call begins.
Before you open anything
Safety
Stop using the oven and unplug it if you see arcing, smell burning or find scorch marks, and do not run it again to reproduce the fault. Never remove the outer cabinet: the capacitor inside holds a dangerous charge long after the power is off, and that is true of an oven unplugged for days. Never defeat an interlock, never run the oven empty, and never reset a breaker more than once on an appliance that keeps tripping it.
When to call a technician
Call as soon as the cavity, the crockery and the circuit are eliminated, because everything remaining is behind a cabinet that an owner must never open. Stop using the oven immediately, rather than testing further, if the small cover in the cavity is scorched or the door is damaged in any way. Bear in mind when you decide that this is a retailer house brand built by a contract manufacturer, so parts come through the retailer rather than from a brand service network.
Nearest pages of this class
What this page does not cover
This page covers the Criterion microwave as a class, not one family or model line. Component layouts, cavity materials and service procedures all change from build to build and are deliberately not here. Where a family or model page exists for your oven, it is the more specific answer and the one to read first.
Lead Appliance Repair Technician · 12 years experience
Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
