Opener does not respond; display shows E4 or four flashes; internal fuse may blow repeatedly.

Safety: Turn off power at the breaker before opening the FAAC control housing. Verify absence of voltage with a tester if available.

• Check mains supply: Confirm the outlet or dedicated circuit feeding the opener has correct voltage using a multimeter or by plugging in a known-good device.
• Inspect fuses: Open the FAAC control box and locate the primary and low-voltage fuses. If a fuse is blown, replace it only with the same type and rating printed on the board or in the manual.
• Disconnect accessories: Remove wires from accessory terminals (photocells, key switch, external receiver) and try powering again. If E4 clears, reconnect accessories one by one to identify a shorted device.
• Check transformer output: With power on and extreme caution, measure the AC or DC output of the transformer at the board terminals. If there is no low-voltage output and fuses are intact, the transformer is likely faulty.
• Inspect for visible damage: Look for burnt components or tracks on the FAAC PCB. If present, the control board should be replaced rather than repaired on-site.

If you are not comfortable working around mains voltage, contact a qualified technician. Do not bypass fuses or use higher-rated fuses.