liftmaster door opener problem

[8up5.0]

i have a liftmaster /chamberlen formula 1 . 1/2 hp . part # 41A5483-4B .
manf.1/04

the door and light bulb operate normally with the remotes , but when the door is open and someone comes inside or leaves the garage the light bulb does not come on i do not hear the relay click and the learn led flashes randomly ( not the same number of flashes every time).
the motion sensors are glowing green and amber and the green one goes out when i block their line of sight.

[kencraw]

It sounds like the logic board is faulty. The part number you give is not for the opener but it is the number for the logic board. It is possible that moisture could be shorting out the board. Unplug the opener from the ceiling outlet and remove the lens cap. Remove the light bulb and the screws securing the board to the opener. The screws are 1/4-inch hex heads. Pull the logic board away from the opener slowly and look for any moisture before disconnecting wires. If there is moisture, dry it off with a clean cloth. If there is no moisture, place pieces of masking tape around the wires connecting to the board and write the location on the tape with a pencil.

Take the board to a garage door dealer that sells or install Liftmaster openers. Overhead Door Corp is a national dealer with a center near you.