Yesterday I bought a Pioneer 109 DVD burner and not 30 seconds after taking it out of the shop, accidentally dropped it on the ground from about 5 feet up.
When I got it home and powered it up the tray wouldn't open, so it was taken apart and examined. The motor that runs the tray had broken the connection to the PCB it was connected to. It seems the motor isn't really mounted in the drive, it is only located by the pins that solder to the PCB.
The motor has been connected up and the drive reassembled.
The only tests I have done since then is I have burned a RW disk that would work in my old drive, and burnt 1G of data to a DVD-R disk, both succesfully burnt and reread in other drives.
Hopefully I haven't done any more damage than the tray motor.
Just thought I'd share this story, for interest and amusement.