Refrigerator displays EC90; may indicate communication issues between user interface and main control board.

Safety first: Disconnect power before removing control panels or touching electronic boards. Use anti‑static precautions.

Step 1 – Power reset

• Turn off the circuit breaker or unplug the unit for at least 5 minutes.
• Restore power and check if EC90 clears temporarily. If it returns, proceed with inspection.

Step 2 – Inspect user interface connections

• Remove the control panel or display bezel carefully to access the user interface board.
• Check the ribbon cable or harness for secure seating and no visible damage.
• Disconnect and reconnect the cable to clean contacts.

Step 3 – Inspect main control board connections

• Access the main control board (often at the top or rear of the unit).
• Verify that all connectors, especially communication cables, are fully seated.
• Look for burn marks, corrosion, or swollen components on the board.

Step 4 – Replace faulty board if identified

• If the user interface is unresponsive, missing segments, or physically damaged, replace the UI board.
• If the UI appears normal but EC90 persists and the main board shows damage, the main control board may need replacement.

When to call a professional: Board‑level diagnosis and replacement are best handled by a Sub‑Zero technician, especially if firmware updates or configuration are required.