Microwave shows F5 and will not start; sometimes appears after a power surge or lightning event.

Safety: Turn off power at the breaker and unplug if possible. High-voltage components can be lethal; do not probe the high-voltage section.

• Power reset: Leave the unit disconnected from power for at least 15 minutes to allow capacitors on the control board to discharge. Restore power and check if F5 returns.
• Check for burning: Remove the control panel and visually inspect the Viking main control board for burnt spots, cracked solder joints, or melted components.
• Verify line voltage: Ensure the outlet or circuit is providing stable voltage (typically 120V in North America). Fluctuations can damage the board.
• Replace control board: If F5 persists and no external issues are found, replace the main control board with the correct Viking part number. Transfer all wire connectors one at a time to the new board, matching positions exactly.
• Surge protection: After replacement, consider using a surge protector rated for microwaves to reduce future board failures.