Microwave displays E4 and will not start, sometimes after a power surge or outage.

Safety: Unplug the microwave before touching any internal components.

Reset procedure:

• Unplug the microwave for at least 5 minutes to allow the control board to fully discharge.
• Plug back in and check if the E4 code clears. If it does, reprogram the clock and test a short heating cycle.

Keypad and board checks:

• If E4 returns, unplug again and remove the outer cabinet.
• Inspect the ribbon cable from the keypad/control panel to the main control board. Reseat the connector carefully, ensuring it is fully inserted and not corroded.
• Look for obvious burn marks, bulging capacitors, or damaged components on the control board.

Next steps: If reseating the ribbon cable and power reset do not clear E4, the control board's memory or microcontroller is likely damaged. Replacement of the main control board is typically required and is best done by a qualified technician due to the proximity of high-voltage components.