SAMSUNG HT-Z Plays DVDs but not CDs, Why?

[Old Sparky]

Different laser for CDs - different wavelengths... It's entirely possible that the CD laser has a problem but the DVD laser remains working.

Mark - As far s I know there is only one lasr in this machine, or at any rate on;y one laser lens, which I cleaned, although I haven't checked any individual diodes on the Pickup assembly, nor yet checked price/availability of a replacement Pickup assembly.