Microwave display shows E04 and unit will not start; sometimes accompanied by tripping the household breaker.

Safety first: Unplug the microwave immediately if it trips the breaker or shows E04. Do not repeatedly reset the breaker and retry.

• 1. Visual inspection: Remove the plug from the socket. Inspect the power cord for cuts, burns, or crushed sections. Replace the cord if damaged.
• 2. Check internal signs of short (for trained persons): Remove the outer cover. Look for burnt connectors, melted insulation, or scorch marks around the high-voltage transformer, diode, and magnetron. Any visible damage indicates parts must be replaced.
• 3. Test components: With the capacitor safely discharged, test the high-voltage diode for short, and check the magnetron for continuity to chassis (it should not be shorted to ground). Replace any shorted component.
• 4. Inspect mains filter: Check the mains interference filter (line filter) near the power cord entry for bulging, cracking, or burning. Replace if defective.

Warning: Because this fault involves potential fire and shock hazards, internal diagnosis and repair should be left to a qualified technician.