Microwave runs but no heat; E03 appears after a short time

Critical safety warning: The high-voltage section (transformer, capacitor, diode, magnetron) can store lethal voltages. If you are not trained in microwave repair, do not attempt to service these parts yourself. Always unplug the unit before any inspection.

• 1. Basic confirmation: Place a cup of water inside and run for 1–2 minutes. If the turntable and light work but the water remains cold and E03 appears, the fault is in the heating circuit.
• 2. Visual inspection (low-risk only): With the cabinet removed, visually inspect the high-voltage area without touching components. Look for burnt connectors, obvious arcing marks, or a cracked magnetron antenna cap.
• 3. Listen for abnormal sounds: A loud humming or buzzing from the transformer area combined with no heat often indicates a shorted diode or capacitor.
• 4. Do not attempt to discharge the capacitor or remove the magnetron unless you are qualified. These procedures require proper tools and training.
• 5. Recommended action: For E03 on OK microwaves, the usual repair is replacement of the magnetron and/or high-voltage diode and capacitor as a set. This should be done by a professional technician due to safety and radiation shielding requirements.