Sony DVD DDU1621

Hi Can anyone shed light on my problem with my Sony DVD-Drive DDU 1621

The CD Tray will not eject if there is no disc in the drive, the problem seems intermittent
I have to use manual eject thru the Pin hole.

but will eject with no problem if there is a cd in the drive.

can anyone explain to what is the cause of this problem?

thanks,
summer