Microwave runs but does not heat; display shows E3 after a few seconds of operation.

Critical safety warning: The high-voltage section (transformer, capacitor, diode, magnetron) can store and generate lethal voltages. Do not attempt to test or discharge the capacitor unless you are trained and equipped. Many regions require licensed technicians for this work.

User-level checks:

• Confirm symptom: Place a cup of water in the oven and run for 1–2 minutes. If the turntable and light work but the water remains cold and E3 appears, the issue is in the high-voltage or sensing circuit.
• Check power supply: Ensure the unit is on a dedicated outlet and not sharing a circuit with heavy loads that could cause voltage drops.
• Inspect for obvious damage: With the unit unplugged and cabinet removed, visually inspect the high-voltage area (without touching): look for burnt smell, charred wires, or melted insulation around the transformer, capacitor, and magnetron.

Technician-level actions (for reference):

• Test the high-voltage diode and capacitor with appropriate meters.
• Check transformer primary and secondary windings for continuity and shorts.
• Test magnetron filament continuity and inspect for arcing damage.

Recommendation: Due to the danger and specialized tools required, contact a qualified appliance technician to diagnose and replace the failed high-voltage component.