My LA400 liftmaster gate arm stopped opening. When using remote alarm goes off. Checked diagnostic in control panel - flashes twice - manual shows this to be arm disengaged. I've checked voltage on battery and is good. Nothing looks bad in control panel. Guessing a switch inside arm is not working. Any suggestions on troubleshooting problem before I go through effort of changing motor with siwtches?
I would try disengaging the control panel and then re-engaging it using the manual release key. Once this is done, turn the save switch to the off position and power down the system completely (removing both batteries and 24V transformer input). Once powered down, reapply both batteries and transformer plugs, wait for the board to boot up and turn the save switch back to the on position.
If you're still getting a diagnostic light flashing indicating that the motor is disengaged, then try switching the motor outputs over and see if the diagnostic light changes from 2 flashes to 3 flashes. This will prove that the fault has moved with the arm and not stayed with the same motor output on the board.
I would imagine that it is just a minor glitch with the sensor on the manual release lever, but if it needs replacing, please contact us on 0845 054 5070 for a price on spare parts.
Kindest regards,
Dave