Do you hear the motor humming but the sprocket is not turning? Sounds like your gear is bad.
Does your operator run when you press your wall button, remote button, mini remote, but your door is not moving up or down and you hear a humming sound? Sounds like your gear is bad. Take the cover off of your motor head. Do you see white shavings from your drive gear? Then replace your gear and lubricate each tooth of the drive gear with a low temp grease.
Compatible with many chain drive garage door openers such as Chamberlain Liftmaster, Sears Craftsman, Garage Master, Raynor, Master Mechanic, Security +, Access Master, Elite Series manufactured 1984 to current (Please see the back of your motor head for your manufacture date)
Compatible with part numbers: 41A2817 Gear Kit and 41C4220A Gear Assembly