LiftMaster garage door opener will not run; both UP and DOWN arrow LEDs on the logic board flash simultaneously.

Safety first: Disconnect power to the opener at the outlet or breaker before touching any wiring or circuit boards. Do not work on the opener with the door in the open position unless it is securely clamped to the tracks.

Step-by-step:

• Power cycle the opener: Unplug the opener for 60 seconds, then plug it back in. Check if the LEDs return to normal and the unit responds.
• Disconnect accessories: Remove all low-voltage wires from the terminal strip (wall control, safety sensors, external receivers). Power the unit again. If the LEDs stop flashing and the opener runs from the learn button, an accessory or wire is shorted.
• Inspect the logic board: With power disconnected, remove the opener cover and visually inspect the logic board for burn marks, swollen components, or corrosion around connectors.
• Test operation from the learn button: Reconnect power and press the LEARN button briefly. If the motor still does not respond and the LEDs continue flashing, the logic board is likely defective.
• Replace the logic board: Order the correct LiftMaster replacement logic board (match model and part number printed on the board). Transfer any wiring one terminal at a time to the new board, mount it, and reassemble the cover.

When to call a pro: If you see extensive board damage or are not comfortable working around electronics, have a qualified garage door technician replace and program the logic board.