Ok, so I tried this motor this time!
But again no information on the Internet or on NIDEC website.
Only found that it is a small Brushless DC motor, and that there is a switch contactor on the board.
So this Brushless DC motor is build with a permanent magnet rotor and 9 poles wired around stator. 3 Hall sensor are labelled H1, H2 and H3 on the board, they are used to identify the rotor position. The motor command is 3 PWM signals that are used to create the magnetic field that will make the motor work.
On the following picture the wiring of the 3 poles is identified :
I didn't have a dead board so I couldn't destroy it to identify the whole schematics ! Here is what I got :
?? means that I couldn't make measurements on the board.
There are several traces that go under the spindle motor mostly to the Hall sensors, but I couldn't identify the schematics.
Well next step will be the associated connector on the main board which seems to lead quite easilly to the BD2956FS. And in fact the goal will be to have the interconnexion between the 2 motor controllers and the 4 associated connectors.
If I have some time it would be fun to open a dead optical module to get some clues on its connector's pinout and functions.