Microwave display shows E04 and unit will not start; sometimes accompanied by a loud humming noise before error appears.

Safety warning: This error indicates a potential high-voltage short. Do not repeatedly attempt to start the microwave, as this can damage additional components or cause fire.

Basic user checks:

• Inspect the interior cavity, including the waveguide cover (mica plate on the side wall or ceiling), for burn marks, melted spots, or metal objects left inside.
• Remove any damaged waveguide cover fragments and do not operate the unit until replaced.
• Ensure no metal utensils, twist ties, or damaged cookware are used.

Technician actions (overview):

• Unplug and discharge the high-voltage capacitor safely.
• Test the high-voltage diode, capacitor, and magnetron for shorts with appropriate equipment.
• Inspect the waveguide and cavity for arcing damage; replace the waveguide cover if contaminated with food or carbonized.

Note: Because of the high risk, this repair should be carried out by a qualified technician familiar with Teka microwave high-voltage systems.