Electric cooker oven troubleshooting and repair: Sparking and Arcing: Diagnosing Microwave "Lightning" very easy £5 fix

⚠️ Safety Note: Don't Let it Burn!

If your microwave starts sparking, stop it immediately. Continuous arcing can cause permanent damage to the magnetron (the most expensive part) or even burn a hole through the metal cavity wall, rendering the unit unsafe and non-repairable due to radiation leakage.

This piece of card is a mica wave guard very cheap to replace or try to clean it first with soapy water and let it dry before refitting and testing microwave again. The new piece will need cutting to size so keep you old one for a template.

Few things are more alarming than seeing sparks and hearing a loud crackling sound inside your microwave. This "arcing" is essentially electricity jumping through the air, but it usually doesn't mean the appliance is a write-off. It’s often caused by a simple maintenance issue or a cheap, replaceable part.

The Repair Process

The Waveguide Cover (The #1 Culprit): Look inside the cavity for the small, cardboard-like rectangle on the side wall. This is the mica sheet (waveguide cover).
- The Fault: Over time, food splatters onto this cover. Because food contains carbon, it absorbs microwaves, heats up, and eventually burns. Once it carbonizes, it becomes conductive and begins to "arc" to the metal frame.
- The Fix: Remove the cover. If it has a burnt hole or dark carbon marks, replace it immediately. These are inexpensive and can often be cut to size from a universal sheet.
Exposed Metal/Paint Damage: If the internal paint has chipped or bubbled, the bare metal is exposed.
- The Fault: Microwaves reflect off the walls, but if they hit a sharp, exposed metal edge, the concentrated energy can cause a spark.
- The Fix: Sand down the area and apply specialized Microwave Cavity Touch-Up Paint.
Burnt Magnetron Cap: If the arcing continues after replacing the waveguide cover, the "antenna" of the magnetron behind it may be burnt.
- The Fix: This requires opening the chassis (Safety Warning applies). If the metal cap on the end of the magnetron is pitted or burnt, it needs replacement or the magnetron itself may be faulty.