Tray is stuck inside

I know this problem has been asked quite a few times, but this is somewhat different. On my SONY    DVD RW DW-Q120A, the tray is stuck only when there's no disk inside the device.
When there's a disk inside, the tray happens to come out freely.(Although not so much lately, irrespective of the Disk in the drive, the drive won't open these days)
I had opened the drive but couldn't find much to work with. The Elastic band seems to be fine. How do I know if the band is elastic enough?..any tricks?

Is there any way I can get a schematic of the device?

Regards,
Amit