Not sure if it's a common problem for those internal plastic tabs to break off during shipping, but I also had that happen to one of the units I purchased on eBay...I was able to get it working and get the CD/HD tray lined up correctly...
Not sure if it happened during shipping or if the previous user hosered it up...But I slapped in a 120GB drive on a removable caddy with the ribbon extension cable and I'm rippin' and burnin'.....Good luck,
Randy
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Happy owner of 2 Centrals, 2 Empegs Mk2a 160GB, 1 Empeg Mk2a 60 GB, a Rio Riot, 4 Rio Receivers, and two 1GB iPod Shuffles...