I use the 640c in a second system consisting of a Nad c325bee & Quad 21L2s. It recently stopped reading discs. I was told by the US distributor that the repair should be no more than $150. In your opinion is it worth the fix.
Chances are the laser has burned out. This happens. You may want to check with a local repair shop to see if the work could be done for less. Of course this would void any warranty but maybe the unit is already out of that already?