Note: this is how i diagnozed my GPS : 1/ the screen was lifting up from the dashboard as expected, and was announcing the “cannot read disc blablabla” so it wasn’t a problem of hardware logic (or power). -> i can continue looking further (if your problem is erratic behavior of the software, then you’re most probably fucked). 2/ i could hear the disk spindle on start up (quickly turn the key in first position and run to your trunk and stick your ear to the dvd thingie) and the reader would attempt several tries before stopping – it was the only motor i could hear 3/ i opened the gps and used a 5V power supply on the contact of the carriage motor (just apply wires with your hand) to make sure the motor could move, and it did, BUT once every 5 attempts and drawing a whole lotta more current than it should have.

Note 2: i simplified the process above -> if you have bad luck (as i had initially) the motor failed before the carriage could return home (there’s a little black stop switch on the travel of the carriage, near the motor for detection) and then, because the carriage can’t reach the end switch, the read disc procedure cannot start – the disc won’t spindle on start up, because carriage doesn’t return home; so don’t jump to the conclusion that the spindle motor is bad, check for the carriage position when you open it – just open the gps and unscrew the little guide joining the carriage and the endless screw, move it all the way to the end switch and try it again on your car. you should hear the spindle, and the squeaking of the carriage motor; if neither, then you can say the spindle motor or spindle driver output (same ship as the other motors) is dead

I hope it can help someone else, because volvo asked me for 815 euros to replace the dvd player/gps ;)… and i did it with elbow grease, jedi mind tricks and 30 bucks (1.5+5.5 + shipment costs)