This seems to be a manufacturing problem. When the disk is loaded it is centered on a spindle and to make sure that centering succeeds a magnet mounted to a small white rotating plastic piece on the top of the DVD drive. The magnet seems to bee too strong on my machine so the spindle isn't able to disengage when trying to open the tray. The result is blocking. It is of course possible that the electric motor moving the tray and the spindle movement is too weak. Anyhow this is how I solved the problem on my Philips Video/DVS DVDR3510V:
1) Disconnect the device from mains power.
2) Unscrew the eight screws holding the top in place.
3) Unscew four black screws keeping the DVD unit fixed to the main body.
4) Carefully drag the DVD slightly back which allows you to rotate it to point sideways (this allows simpler testing of the mechanical working).
5) Unscew the two blank screws keeping the front half of the top of the DVD unit in place.
6) Using a small screw driver carefully bend the clips to allow the top plate to be removed.
7) Connect the mains power and don't ouch anything inside.
8) After startup try Eject/Load several times to ensure that the DVD unit is mechanically working OK. If the Eject/Load doesnt work with the top off there is no use going further.
9) Disconnect mains power.
10) Use a small felt tipped pen to mark the face of the small metallic (magnet) part in the center of the white movable component fixed to the top.
11) Using a small flat screw driver carefully open the clips holding the two halves of the white component together. Careful! The clips may break easily.
12) Cut small pieces of tape (or use thick drawing paper). The idea is to lift the magnet slightly upwards. We thus use tape or paper as shims. Notice that a hole is needed in the center.
13) When the shims are in place put the magnet back oriented correctly (if you didn't mark it test it against the spindle rotating the disk. The correct orientation is where the magnetic force is strong.
14) Mount the halves back into the hole in the top component and align the clips. Then press the halves together until the clips connect.
15) Put the top component back and clip it into place. No need to screw in the screws yet.
16) Connect mains power, don't touch anything inside.
17) Check that the tray now opens both with a disk and when empty. Check that a DVD is recognized correctly (too little pressure leads to disk loading failure).
18) If the DVD unit now works assemble it and you are done.
The first picture shows the white round plastic part that is modified on the left hand side of picture.
The second picture shows an additional support I glued to the top with super glue because the top is fairly flexible. Initially I thought this was the reason why the spindle got stuck. I think the extra support is unnecessary but i didn't bother with removing it.