@amp: good post man, the cybermag link is perhaps the best online manual for laser maintenance (especially in dealing with v.9-10 consoles) that i've seen.
@Cafn: i have a total of 4 consoles. one of them is still in pristine condition and other one i just fixed (1 beyond repair and the other waiting for a few parts).
one of my v.9 consoles had a laser that would only read PS1 discs and it wouldn't even read original & back up dvd discs or even a dvd movie disc. i searched for all of the info that i could dig up on this specific issue and the best result was the link that amp posted previously. i did read a few posts about users who were also had the same problem with their consoles but they were clueless as what to do about it.
my conclusion was, that laser is just out comission now and a new replacement was needed.
the v.9 ps2 originally came with a khs-400c laser and i bought the same model replacement on ebay for $30!! all laser replacements on ebay are pretty much refurbished lasers but will do the job.
i decided to install the 400c laser on my v.4 or 5 console which came originally with a 400b laser. the install was cakewalk man but the only hassle was hooking back up the ribbon cables that connect both to the laser and mobo. the fat ps2 consoles are very friendly with other parts belonging to other model versions.
use these links are reference sources to help you with replacing your laser,
PS1/SCPH-7501 | MM3 modchip
PS2 v9 | 250GB hdd | PS3 component cable | katana 32mb mc
PS3/CECH-2001B | 250GB hdd | 3.65 ofw