The short version
A TM microwave showing electrical symptoms is not a fault to work through with the appliance running. Unplug it first, then establish which of the three common causes applies, and treat anything beyond those as a technician's job.
The observable signs on this platform
- Scorch marks or a burnt patch on the small panel in the cavity wall — The waveguide cover. Once it is marked, arcing concentrates there and recurs until the cover is replaced.
- A burning smell from the cabinet rather than from food — Unplug it and leave it unplugged. This is a component smell and there is nothing for an owner to inspect.
- The breaker trips when the machine runs — The protection is working. Do not keep resetting it — that is how a fault becomes a fire.
- NEAR MISS — the machine runs normally but does not heat — No heat without any electrical symptom is a high-voltage component fault rather than a safety event.
Causes, most likely first on the TM family
- Metal in the cavity — First on this family and the most common cause of arcing by a wide margin. Metal trim on a plate, a twist tie, a fork left in a bowl, or foil on a package all arc, and none of them is an appliance fault.
- Damaged or carbonised waveguide cover — Second. Food spatter bakes onto the cover, carbonises, and becomes a conductive spot that arcs.
- Carbonised food residue on the cavity walls or the roof — Third. Long-baked spatter behaves the same way as a damaged cover.
- Failing high-voltage component or a shorted magnetron — Fourth. This is the burning-smell and tripping-breaker class, and it ends owner involvement. Unplug and call rather than testing.
The order to work in, and the reason for it
- 1. Stop the cycle and unplug the machine — Before anything else, and regardless of which symptom brought you here.
- 2. Look at what was in the cavity — Metal trim, a twist tie, foil, cutlery. If the arcing coincided with a particular dish, the appliance may be entirely sound.
- 3. Inspect the waveguide cover and the cavity walls — You are looking for scorch marks and carbonised residue.
Safety first
Safety
Unplug the appliance or switch off its breaker before removing any panel. A capacitor can hold a charge after the power is off, and in a microwave oven that charge is lethal — do not open the cabinet, do not attempt to discharge anything, and do not look for a fuse. Never run a machine that has arced until you know why it arced, never reset a breaker repeatedly, and never put metal of any kind in the cavity.
Models in the TM family — The model numbers this page covers.
Reference| Model number | Family key |
|---|---|
| TM034D3MG-P00D00 | bertazzoni:microwave:tm |
| TM038K6BH-P0HA00 | bertazzoni:microwave:tm |
| TM048K6BF-P0HA00 | bertazzoni:microwave:tm |
When to call a technician
Call immediately, with the machine unplugged, for any burning smell from the cabinet, any smoke, any tripped breaker or any warm plug or lead. For arcing, clean the cavity and eliminate metal first — if it then recurs with a clean, undamaged cavity, that is a technician's job because the waveguide cover and everything behind it are not owner-serviceable. Do not keep using the appliance while waiting.
Other problems covered for the TM family
Lead Appliance Repair Technician · 12 years experience
Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
