I have just been told that the laser in my 15 years old Marantz CD80 is on
the edge of the red zone and that it is likely to fail in the not so
distant future. Can anyone tell me what this actually means? How are lasers
tested, does a laser ‘in the red zone’ perform worse musically or will it
just become more difficult for it to recognise disks?

--
Luuk Houwen
Hattingen
Germany

I have just been told that the laser in my 15 years old Marantz CD80 is on
the edge of the red zone and that it is likely to fail in the not so
distant future. Can anyone tell me what this actually means? How are lasers
tested, does a laser ‘in the red zone’ perform worse musically or will it
just become more difficult for it to recognise disks?

The laser diodes used in CD players do "age" over time. The laser's
optical output level begins to drop. Eventually, the amount of laser
light being emitted by the laser, and reflected from the disc, becomes
low enough that the photodiode(s) and tracking/decoding electronics
cannot read the signal cleanly. When this happens, the CD player may
begin to mistrack, or the bit-error rate of the data may increase to
the point where it overwhelms the error correction circuitry and you
begin to hear pops, clicks, stutterings, and so forth.

I'd guess that "red zone" is some manufacturer's term for an output
level which is low enough that mistracking or mis-reading may be
likely. This could be determined by actually measuring the laser
output, or by looking at the amplitude of the "eye pattern" (the
output of the photodiode and preamplifier, viewed on an oscilloscope),
or by looking at the bit error rate of the data stream.

It's sometimes possible to _temporarily_ correct the problem by
boosting the laser diode's operating current level (there's often a
small trimpot on the PC board to do this). However, the increased
current tends to cause the laser to age even more rapidly - it's a
slipperly slope which leads downwards to total failure of the laser.

Replacement of the laser diode subassembly is sometimes, but not
always possible (it depends on the specific transport mechanism), and
some amount of physical and electrical realignment is likely to be
necessary.


--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

In article kql6c.35270$J05.225582@attbi_s01,
Luuk Houwen wrote:

I have just been told that the laser in my 15 years old Marantz CD80 is on
the edge of the red zone and that it is likely to fail in the not so
distant future. Can anyone tell me what this actually means?

That the laser's output is getting low (they do wear out over time).

How are lasers tested

Not sure. Probably by measuring the output directly, or by looking at
the "eye pattern" of the data recovered from the disc.

does a laser ‘in the red zone’ perform worse musically

No. It either works or it doesn't. In a very marginal situation, there
might be drop-outs. They would ba audible as skips in the sound.

or will it just become more difficult for it to recognise disks?

Probably, and probably some discs before others. Eventually, it won't
work at all. There is an adjustment for the current passed through the
diode to make it lase. Possibly the lifetime could be extended by
adjusting it. Also, possibly, the laser will be destroyed. If it doesn't
work anyway, that may not matter.

Isaac

Luuk Houwen wrote:

I have just been told that the laser in my 15 years old Marantz CD80 is=
on=20
the edge of the red zone and that it is likely to fail in the not so=20
distant future. Can anyone tell me what this actually means? How are la=
sers=20
tested, does a laser =C2=91in the red zone=C2=92 perform worse musicall=
y or will it=20
just become more difficult for it to recognise disks?
=20
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3 D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3 D=3D=3D=3D=3D=3D=3D=3D=3D=


With age and use, laser intensity decreases. Once it drops below a=20
certain level, tracking becomes insecure, and the player may skip or=20
simply refuse to play. Before that, its read-error rate will increase,=20
and any error correction in the player will be working harder to make up =

for the errors, resulting in degraded sound. When this happens,=20
replacement of the optical pickup assembly is necessary. Some CD player =

manufacturers supply the replacement as the entire CD mechanism,=20
including optical pickup and both the tracking and spindle motor, thus=20
replacing all the mechanical parts involved in spinning and tracking the =

CD, in addition to the laser.

As for "red zone," that term is an invention of whoever checked the=20
laser for you. Hopefully a laser intensity meter was used. Perhaps the =

meter has a red zone on its dial that suggests intensity is not what it=20
should be.

With regular use, some players' lasers go out of spec in as little as=20
four to six years. If you have been using your Marantz CD 80 regularly=20
for 15 years, I probably would agree with the assessment of a weakening=20
laser. I always recommend replacement be made with OEM parts;=20
especially for the popular Sony Chemical laser pickups, there are=20
aftermarket knock-offs that sell for somewhat less money but don't=20
perform as well, or for as long a time. Also, some optical pickups fail =

not because of a weak laser, but because of mechanical problems, most=20
commonly a weak centering spring, which holds the laser assembly,=20
against gravity, in the proper position so that the focus coils will=20
start from a known "neutral" position when focusing on the recorded=20
pattern of the disc.

In article , Gene Poon
wrote:

With age and use, laser intensity decreases. Once it drops below a
certain level, tracking becomes insecure, and the player may skip or
simply refuse to play. Before that, its read-error rate will increase,
and any error correction in the player will be working harder to make up
for the errors, resulting in degraded sound.

That's not the way it works. The error correction is "working hard" all
the time. Actually, it just "works", doing the same thing no matter how
many errors there are (which is almost always -- none). It's just a
bunch of mathematical calculations, performed on the bitstream along
with all the other things that happen to the data before it gets sent to
the DAC.

As long as the correction procedure is effective, the resulting
bitstream is *perfect*. Period. When the number of errors is so large
that the correction algorithm fails, it *knows* that it failed. At that
point, most players invoke a "concealment" procedure, substituting a
"best guess" for the sample that couldn't be recovered. Perhaps you can
hear that. Maybe. Probably not.

If the error is so bad that all the above is useless -- not just one bad
sample, but a long string of unrecoverable data -- the player probably
mutes the output briefly. Depending on exactly what the data stream is
at that instant, you might be able to hear that.

In any case, I certainly would not call muting "degraded sound"; I'd
call it a "drop out". As long as the error correction works, there is no
degradation *at all*. None. A weak laser would probably deliver a large
percentage of uncorrectable data (from some discs; others might read
perfectly), and the result would probably be full of dropouts; very
audible.

Bottom line: I don't think the result of a weak laser would be a subtle
change in sound; it would be quite obvious, and not "degraded", but
unlistenable.

Isaac

Isaac