Running a microwave oven empty for an extended period, such as the 3 minutes you mentioned, can indeed cause damage to the magnetron—the component responsible for generating the microwave radiation that heats the food. When a microwave operates with no food or liquid inside, the microwaves have nowhere to be absorbed, which can lead to a buildup of energy within the oven.
The burning smell and the microwave being hot to the touch are clear indications that something went wrong during the empty run. The magnetron likely endured excessive stress, and it might have sustained damage or developed a fault as a result. In some cases, the magnetron may fail entirely after such an incident.
Using a microwave oven with a damaged or faulty magnetron is not safe. A malfunctioning magnetron can pose risks, such as increased radiation leakage or potential electrical hazards. It is crucial to avoid using the microwave until it has been inspected and repaired by a qualified technician.
If you notice any unusual behavior or smells coming from your microwave, or if it remains hot to the touch after a short period of use with food inside, immediately stop using it and have it checked by a professional before attempting to use it again. Your safety and the safety of others are of utmost importance when dealing with microwave ovens and potential radiation hazards.