Denso Nav problem in toyota camry

my denso 462100-0436 Nav system in the 2002 camry has trouble reading the DVD disk. The disk looks ok, and reads OK on my home computer and laptop, but the system says it can't read the disk. For a while, Ejecting the disk and re-inserting will get the NAV computer to try again, and often that will cause it to work ...for a while...then the problem reappears again when the car is started. I have disassembled the unit (I'm and electronics engineer) and checked all of the flex cable connections, inspected for apparent problems, and checked the Power supply voltages, which seem to be good. The DVD ROM ( panasonic DVS100-V) apparently uses about 3.6 volts, via a regulator on the 5 volt supply (is this correct??) Any suggestions? Can you tell me where to get schematics? Do you repair such items?