[conspire] Re: CD-RW laser going into failure?

[Dan Martinez]

Eric De Mund <ead at ixian.com> wrote:

> And that fairly consistent position of the first read errors (2/3 to 3/4
> of the way through the disc/data) leads me to wonder, naively, "Can the
> laser no longer sustain sufficient burning strength after it's been on
> (burning) for a certain number of minutes?"
>
> Tell me more about CD-RW versus CD-R discs. I don't believe I have any
> CD-RW discs here with which to perform a test. What's your thinking
> here?
>
> Finally, a five-brush laser lens cleaner disc failed to have any posi-
> tive effect upon this post-burn data verification. I still get read
> verification errors at 65% of the way through the data. I'm thinking the
> drive may simply need to be replaced. Do others here get more use out of
> a CD burner than the 12-18 months of heavy use I seem to get?

Eric, I don't know that this is anything more than a shot in the dark,
and I don't know that it's going to be of much use to you even if it's
not, but the fact that the errors seem to consistently occur at the
same point in the disc leads me to wonder whether another factor isn't
involved.

Consider the fact that a point on the periphery of the disc is
travelling considerably faster than a point near the center. To expose
a point on the outside of the disc to the same amount of laser energy
as a point on the inside, you either have to ramp up the power of the
laser, or reduce the rotational speed of the disc.

Different manufacturers have adopted different recording strategies to
deal with this fact. These go by an assortment of acronyms: CAV
(Constant Angular Velocity, keeping the rotational speed of the disc
constant throughout the write operation) CLV (Constant Linear
Velocity, modulating the speed of the disc so that the laser hits
every point on it for the same duration), plus hybrid approaches like
PCAV (Partial Constant Angular Velocity) and Z-CLV (Zone-Constant
Linear Velocity, wherein the disc is subdivided into a set of
concentric zones, and each is burned at a different constant linear
velocity).

I ran into problems I suspected to be related to these different
approaches back when I had a CD-based standalone MP3 player, and tried
to keep it fed with music burned to a CD-RW. The player would
consistently choke on certain tracks; flipping the CD-RW over, I could
see that the burned area consisted of a set of concentric rings with
slightly different reflectivity. I theorized (although never proved)
that my player was being confused by the transition from one zone to
another.

I wonder if you're not seeing a related effect. Either your burner
goes though a speed transition at the 65% mark that causes hiccoughs
in the burned data, or maybe you've got a CAV burner, and the laser
can no longer deliver the higher power that the outer regions of the
disc require. I am, as I said, clutching at straws. I don't know if
your burner supports more than one writing strategy, and I don't know,
even if it does, whether there's a way for you to control which one it
employs. But I thought I'd mention the possibility.

If you do decide to replace your burner, I've always been very pleased
with Plextor drives, especially the 716 series.

Cheers,
Dan