The very FIRST procedure that should be done is to have your NAD
CD
player cleaned.... and also your CD burner. Inspect the suspect
disks carefully for smudges, scratches, warped, etc.

I'll clean the rails and the lens in the player but the cd was
spotless. (I keep a clean microfibre cloth in the stereo stand just for
cds.) The ratio appears to be about 1 in 20 (rather frustrating).
I've heard of a 'focus coil transistor' problems but I'm not sure which
trannys are in question.