It may very well be the stepper motor or the motor driver. Disconnect the power and open the case by removing the five (5) screws on the back and the three (3) screws on both the left and right sides. Before removing any of the flexiable white cables, clearly mark them so that they easily reinstalled. Remove the dvd/cd read assembly; there are four (4) screws holding it to the case. Look for the motor manufacturer and possibly a part number. I MUST WARN YOU... THE POWER SUPPLY CIRCUIT IS OPEN AND THE CAPACITORS ON BOARD CAN AND OFTEN DO STORE LETHAL VOLTAGES. IF YOU ARE NOT EXPERIENCED WITH AC / DC ELECTRONIC REPAIR, FIND SOME TO HELP YOU OR DO THE WORK FOR YOU.
HAVE FUN WITH YOUR REPAIRS,
TMM
Trevor, January 2008