Hi , I'm just wondering if it's possible to adjust or at least verify the
laser of a DVD or CD player without a laser beam checker.

I have a 500MHz scope and a god expertise in electronics but never play with
DVD/Cd laser Assy.

Problem is the DVD player doesn't play always the DVD inside , lens has been
cleaned.

I'm assuming that these steps are standard for all tha models.

Also , what is the difference between the laser of a DVD and a CD ?

Why a DVD laser can read CD and not the inverse.

Thanks a lot for your help.