I know this thread is old but just wanted to say thank you - I now got my drive working and the top of the bluray back on as well.
I have one of the newer bluray drives on the fat ps3 so all the youtube vids didn't really help. It seems in sony's attempt to reduce the cost of the ps3 they changed the design of how the tray mechanism works.
Anyway I had taken the drive apart to replace the lens and the rack. This was pretty simple to achieve - but when trying to put it back together again the disc would get pulled into the drive but wouldn't be positioned properly and wouldn't spin. After hours of trying I stumbled upon this thread. Thanks to the images provided I figured the metal arm at the back of the drive was out of position.
Once I placed that back in the drive still wouldn't spin the disk and there appeared to be resistance. The disc should spin freely once fully loaded even if the ps3 is off and you spin it manually.
I wish I had some images to provide as well but it turns out that the loading 'arms' at the front of the drive should not be in contact with the disc at all when it is fully loaded. Mine were still touching the disc and as the 'arms' have rubber contacts that spin it was preventing the disc from spinning. To make is clear, nothing should be in contact with the disc other than the middle spindle and the top magnet. It turns out that the left hand sliding rail is what holds the arm away from the disc. When it slides down the groves catch the arm and hold it back.
After playing around with it for a few hours more and reading tips on here and other sites on the net I finally got it working and reading the disc without the top of the drive on.
Getting the top on was very difficult but in the end I decided the best way to ensure every thing was lined up was to put the drive in the loaded position (easier without a disc) and line up the various components on the lid into the loaded position as well and place it back on top (this is very tricky - don't bother if you have large unsteady hands) and. Got this eventually then placed the magnet in place, switched on the ps3 then pressed the eject button and hoped that the drive would go back to the correct resting position. The eject mechanism worked and the drive went back to the resting position. I inserted a disc and the drive took it with no issues and spun it with no issues and now it works with both DVDs and Blurays (IMG:
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After putting it all back together again I realised I had forgotten to put the screws back on the loading motor. Not sure if I can face opening it up again after all that effort and the fact that it is currently working (IMG:
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Anyway hope this post proves useful for someone else even if it is a bit on the long side.