quick (but maybe difficult) question

I've got a Sony DVD RW DW-U12A in a Sony Vaio computer that's a couple
years old. I know the common answer to the problem I'm having is that
the drive is going--it won't read any CDs any longer, and it's
increasingly not reading DVDs. PowerDVD gives me the good old "A disc
with an unsupported format" message in those cases. I'm only trying to

read commercial prerecorded discs, by the way--not burned discs. I do
have AnyDVD and CloneDVD on my computer, though. And even when those
read discs sometimes, they can't analyze the whole disc--they get to
about 80% or so and CloneDVD locks up. I've tried disabling and even
uninstalling both AnyDVD and CloneDVD to see if they're causing the
problem (because of some other copy protection on the commercial discs,

maybe), but I have the same problems then.

Here's my question. Why, if the drive is going bad, can it read a lot
of discs just fine, but not others, and it's consistent on which discs
it can read and which discs it has trouble with? It must be something
about the way the information is encoded on certain discs combined with

whatever is going wrong, I'm assuming, but what?


Partially, I'm just trying to make sure that the drive is going bad and

that it's not some other problem. I don't want to (and can't really
afford to) spend over $100 for a new drive and it doesn't solve the
problem.


Thanks in advance

 

The laser head is out of calibration or dusted.

I'd be willing to bet that it will read just fine upside down.

The heads sag after a time on their support springs.

The speed at which a burned disc is recorded can affect it's
"contrast ratio". same number of bits laid down with a non differing
laser power will produce this. Older writers didn't vary power so as
write speeds increased, contrast ratio decreases. In other words, the
pits get laid down by impinging less on the polymer layer, producing a
more shallow pit, making the difference between a pit and land less
"apparent". Also, a DVD is read with a different "head" than the CDs
are, even in the same reader.

So, it is either a sagging head and turning it upside down will show
this or it is that you are reading discs that were burned too fast.

Also, as a burned disc gets older, the pits "burned" in it "relax"
rendering it unreadable.

Could be any of those three or combinations thereof.


and it's consistent on which discs