denon dcd-485 cd errors hlp req plz

i bought a used denon dcd-485 hifi separate cd player, it seems to reject bought cd's well almost 90% of them but it plays cdr copies perfectly it will play the odd retail cd though. wha tcould be wrong with it cd's are not scratched what could i try.are replacement lasers for the 485 expensive and where do you get them from,grandata dont sell them for the 485 its the only parts supplier i know of in the u.k
You might try playing with some of the trimpots, mainly the ones you'd find on the transport itself. But before you touch any of them, mark with a sharp pointed magic marker pen (like a Sharpie) lines that cross from the part of the trimpot that would turn to the stationary frame of the trimpot. Purpose of this is that you can return the trimpot to its original setting if you see no improvement from tweaking it. So you can get the player to work as before, and not not work at all... Insert a storebought CD the machine won't play (but will play in another machine). Play with one trimpot at a time, and return it to its original setting if it doesn't fix the problem of not playing store bought CDs.

There is risk of course, but it could solve the problem.