Microwave runs but does not heat food; display shows E03 after a few seconds of operation.

Critical safety warning: The high-voltage system in a microwave (transformer, capacitor, diode, magnetron) can be lethal. The capacitor can retain a dangerous charge even when unplugged. If you are not trained in high-voltage appliance repair, do not attempt internal repairs. Limit yourself to external checks and basic testing.

Basic user checks:

• 1. Confirm symptom: Place a cup of water in the oven and run on HIGH for 1–2 minutes. If the turntable rotates and the interior light is on but the water remains cold and E03 appears, heating has failed.
• 2. Check power supply: Plug the microwave directly into a wall outlet (no extension cord or power strip). Low voltage can sometimes cause HV errors.
• 3. Inspect for burning smell or noise: Listen for loud humming, buzzing, or arcing sounds. A strong burnt odor or loud hum suggests a failed magnetron or transformer.

Internal diagnosis (for qualified technicians only):

• 4. Discharge the capacitor safely: Before touching any HV components, the capacitor must be properly discharged using a resistor and insulated tools.
• 5. Test the magnetron: Remove the magnetron leads and check continuity between the terminals and from terminals to chassis. Replace if shorted to ground or open.
• 6. Test the HV diode and capacitor: Use a multimeter with diode and capacitance functions to verify the high-voltage diode and capacitor are within spec.
• 7. Inspect the HV transformer: Check for burnt windings, smell, or open primary/secondary coils.

Recommendation: For most homeowners, E03 should be handled by a professional due to the high-voltage risks and need for specialized tools.