CD or DVD laser check ...How to ...

M

Maxmel

Guest
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.
 
"Maxmel" <pothier@cae.ca> wrote in message news:dhjn1b$jen$1@dns3.cae.ca...
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.
Click to expand...
There's not really much you can do to make a definitive assessment of a
laser's condition, other than to rely on experience and substitution. Unless
it is part of a manufacturers service setup procedure - Pioneer CD players
for instance - the laser power pots should NEVER be adjusted from their
factory set, and usually sealed, positions. Even a laser power meter won't
tell you a lot about a laser's condition. Even if it indicates that the
emitted power is within spec, plenty of laser problems are caused by
defective pickup chips ( the clear plastic chip usually at the bottom, which
has the individual photo diodes on it ) or dust on the internal optics,
diffusing the reflected beam from the play surface, before it gets to the
pickup chip.

The difference between a CD and a DVD laser, is wavelength and power. A DVD
laser is in the visible red portion of the spectrum, and of higher emitted
power than a CD laser, which is in the infra red part of the spectrum. DVD
lasers do not read CDs or vice versa, in general. Rather, there are two
laser emitter chips, for the two different wavelengths, and usually a single
pickup chip, although these items are all integrated together in a single
pickup head assembly.

If your player handles CDs ok, but struggles with DVDs, theres a better than
80% chance that the problem is the laser.

Arfa
 
I believe a dvd laser can in fact read a cd.. I know a lot of early dvd
players had two lasers to save wear on the more costly dvd laser (and
they do wear out with time), but I thought most modern players used
only a red laser for all media.

It was my understanding that the IR laser in a cd player is just too
"fat" in terms of wavelength to resolve the tin
 
<stickyfox@gmail.com> wrote in message
news:1128149622.896339.122080@g47g2000cwa.googlegroups.com...
I believe a dvd laser can in fact read a cd.. I know a lot of early dvd
players had two lasers to save wear on the more costly dvd laser (and
they do wear out with time), but I thought most modern players used
only a red laser for all media.

It was my understanding that the IR laser in a cd player is just too
"fat" in terms of wavelength to resolve the tin
Click to expand...
It's the reverse. Older players which had the red lasers were able to read
factory cd's with a reduced level of efficiency.
They could not read CD-R's because the discs were essentially "invisible" to
the red laser. Some older red-laser players, like Sony's could read CD-RW's
but not CD-R's. Others would not, but that was a firmware issue.
Newer players don't use two separate lasers - they use a special "double"
laser diode, which emits from one side or the other depending on how it's
biased; that is, for an audio cd or CD-R, or a DVD. Ocassionally, one will
malfuction in such a way that DVD's can't be read anymore, but cd's can.

Mark Z.
 
It was my understanding that the IR laser in a cd player is just too
"fat" in terms of wavelength to resolve the tin
Click to expand...
That was where firefox crashed. I was going to say something about
tinier pits on DVD's..

When you say emits from one side or the other, do you mean that both
ends of the crystal are used as emitters? Or are there multiple diodes
in a single package? I never heard of this; it sounds interesting.

I just assumed that it was a single laser, but I have definitely
observed that a much more powerful looking beam is used to read DVD's
than CD's.
 
<stickyfox@gmail.com> wrote in message
news:1128195413.744952.69200@g14g2000cwa.googlegroups.com...
It was my understanding that the IR laser in a cd player is just too
"fat" in terms of wavelength to resolve the tin

That was where firefox crashed. I was going to say something about
tinier pits on DVD's..

When you say emits from one side or the other, do you mean that both
ends of the crystal are used as emitters? Or are there multiple diodes
in a single package? I never heard of this; it sounds interesting.

I just assumed that it was a single laser, but I have definitely
observed that a much more powerful looking beam is used to read DVD's
than CD's.
Click to expand...
I actually tore apart a dual-wave diode a couple years ago, but I don't
remember exactly how it was built. I do remember it was roughly rectangular
in shape with tiny wires going to it. I only "presume" it was three
connections total, either 3 wires or two wires with a center common
connection.

Mark Z.
 
"Mark D. Zacharias" <spammenot@nonsense.net> wrote in message
news:MnD%e.2264$Fi3.1189@newssvr29.news.prodigy.net...
stickyfox@gmail.com> wrote in message
news:1128195413.744952.69200@g14g2000cwa.googlegroups.com...
It was my understanding that the IR laser in a cd player is just too
"fat" in terms of wavelength to resolve the tin

That was where firefox crashed. I was going to say something about
tinier pits on DVD's..

When you say emits from one side or the other, do you mean that both
ends of the crystal are used as emitters? Or are there multiple diodes
in a single package? I never heard of this; it sounds interesting.

I just assumed that it was a single laser, but I have definitely
observed that a much more powerful looking beam is used to read DVD's
than CD's.


I actually tore apart a dual-wave diode a couple years ago, but I don't
remember exactly how it was built. I do remember it was roughly
rectangular in shape with tiny wires going to it. I only "presume" it was
three connections total, either 3 wires or two wires with a center common
connection.

Mark Z.
Click to expand...
I just had a quick look at a few scrap lasers which were hanging around the
workshop, and they have six connections to the laser diode unit. Looking at
a few schematics, these are one each for the anodes and cathodes of the
laser diodes ( one red, and one infra red for DVD and CD respectively ) and
one each for the feedback photo diode integrated with each laser diode. The
other connection of the feedback diode is commoned with one of the laser
diode connections in each case. The feedback diode is to allow for automatic
power control of the laser output. Laser diodes with only three connections
appear on the regular CD only laser heads. Here, the connections are again
anode and cathode of the laser diode, and one leg of the feedback diode, the
other leg again being common with one of the laser diode legs.

The general sequence of events is that the laser homes and then the red DVD
laser is switched on to burn. The focus sequence is then initiated and, once
focus has been obtained, the disc is spun up, and an attempt is made to read
data from the disc. Sometimes, the disc is spun up at random speed prior to
or during the focus search.

As Mark correctly says, the shorter wavelength red DVD laser is actually
able to read the longer pits on a CD, although not very efficiently. Thus,
once enough data has been gathered to evaluate whether the disc that's being
read is a DVD or a CD ( or even a VCD ), the system control processor will
make an evaluation as to whether the red DVD laser should be left burning,
or the infra red CD one, switched on instead. Other subtle changes are made
as well at this time, including altering servo time constants, and disc base
rotational speed etc. In the case of a DVD, the focus has to be adjusted to
ensure that it's reading layer zero at this time also ( assuming that it has
been informed by some of the early data that's collected, that it's a dual
layer disc that's in there. It's a complicated business, to be sure ...

Arfa
 
Maxmel wrote:

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.


To verify that the laser is operating remove any clamps or items that
Click to expand...
would block your direct view of the lens and glance at it when it should
be reading a disc.
The laser is focused to read a disc that is close to the lens, so it
will not be focused on your eye's retina. While I would not advise
staring at a CD/DVD laser for any length of time, a passing glance will
not cause eye damage or injury even if you do it a thousand times!

However this will not verify the correct output power or the sensor's
ability to read the reflected signal from the disc.
 
"Jumpster Jiver" <me@no.spam.today> wrote in message
news:7XK%e.14881$J03.13211@trndny05...
Maxmel wrote:

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.
To verify that the laser is operating remove any clamps or items that
would block your direct view of the lens and glance at it when it should
be reading a disc.
The laser is focused to read a disc that is close to the lens, so it will
not be focused on your eye's retina. While I would not advise staring at
a CD/DVD laser for any length of time, a passing glance will not cause eye
damage or injury even if you do it a thousand times!

However this will not verify the correct output power or the sensor's
ability to read the reflected signal from the disc.
Click to expand...
Whilst it is probably true that the laser will not cause any eye damage, all
manufacturers recommend that if you must look at it, do it obliquely from an
angle of 45 degrees or so. Also remember that a CD laser is basically in the
infra red spectrum, and emits very little visible light, so can be difficult
to see, encouraging people to try to look closer and directly in the top, to
check if its burning.

The DVD laser can, of course, be seen actually through the disc, so in a lot
of cases where the centre of the disc is not obscured by a large clamp
holder, you can see if the laser is burning with the disc in place.

Personally, I would never look directly into a laser, no matter what the
physics dictates, or how low the power is.

Arfa
 
I just had a quick look at a few scrap lasers which were hanging around
the
workshop, and they have six connections to the laser diode unit. Looking
at a few schematics, these are one each for the anodes and cathodes of the
laser diodes ( one red, and one infra red for DVD and CD respectively )
and one each for the feedback photo diode integrated with each laser
diode. The
snip
Click to expand...

Just to be clear, I was referring to just the laser diode itself, not the
entire pickup.

Mark Z,
 
Jumpster Jiver <me@no.spam.today> writes:

Maxmel wrote:

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.
To verify that the laser is operating remove any clamps or items that
would block your direct view of the lens and glance at it when it
should be reading a disc.
The laser is focused to read a disc that is close to the lens, so it
will not be focused on your eye's retina. While I would not advise
staring at a CD/DVD laser for any length of time, a passing glance
will not cause eye damage or injury even if you do it a thousand times!

However this will not verify the correct output power or the sensor's
ability to read the reflected signal from the disc.
Click to expand...
Keep in mind that if it is trying to read a CD, the wavelength is
780 nm and barely visible. For DVDs, it is like a lase pointer, but
they are both highly divergent.

DON'T look straight down because if for some reason the lens fell out,
the beam may be collimated, which WOULD focus on your retina.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name is included in the subject line. Or, you can
contact me via the Feedback Form in the FAQs.
 
"Mark D. Zacharias" <spammenot@nonsense.net> wrote in message
news:RmP%e.1$dB4.0@newssvr12.news.prodigy.com...
I just had a quick look at a few scrap lasers which were hanging around
the
workshop, and they have six connections to the
Click to expand...
***** laser diode unit. *****

Looking
at a few schematics, these are one each for the anodes and cathodes of
the laser diodes ( one red, and one infra red for DVD and CD
respectively ) and one each for the feedback photo diode integrated with
each laser diode. The
snip

Just to be clear, I was referring to just the laser diode itself, not the
entire pickup.

Mark Z,

I do know the difference between a laser diode and an entire pickup, so I
Click to expand...
was also referring to the laser diode, as I thought that I had carefully
explained, when I said that a typical one, used in a DVD player pickup, has
6 connections, as opposed to one used in a CD only pickup, which has only 3
connections. A complete pickup, either CD or DVD, has many more connections,
than 6.

A CD laser diode has two components in it - a laser diode and a feedback
diode, both integrated onto the same chip. A DVD laser diode, has the same
thing, but times two.

Arfa
 
"Arfa Daily" <arfa.daily@ntlworld.com> wrote in message
news:MCT%e.12292$0w.1516@newsfe5-gui.ntli.net...
"Mark D. Zacharias" <spammenot@nonsense.net> wrote in message
news:RmP%e.1$dB4.0@newssvr12.news.prodigy.com...

I just had a quick look at a few scrap lasers which were hanging around
the
workshop, and they have six connections to the

***** laser diode unit. *****

Looking
at a few schematics, these are one each for the anodes and cathodes of
the laser diodes ( one red, and one infra red for DVD and CD
respectively ) and one each for the feedback photo diode integrated with
each laser diode. The
snip

Just to be clear, I was referring to just the laser diode itself, not the
entire pickup.

Mark Z,

I do know the difference between a laser diode and an entire pickup, so I
was also referring to the laser diode, as I thought that I had carefully
explained, when I said that a typical one, used in a DVD player pickup,
has 6 connections, as opposed to one used in a CD only pickup, which has
only 3 connections. A complete pickup, either CD or DVD, has many more
connections, than 6.

A CD laser diode has two components in it - a laser diode and a feedback
diode, both integrated onto the same chip. A DVD laser diode, has the same
thing, but times two.

Arfa
Click to expand...
OK, but I said I busted one open, and was not counting the monitoring diode.

mz
 
"Arfa Daily" <arfa.daily@ntlworld.com> wrote in message
news:MCT%e.12292$0w.1516@newsfe5-gui.ntli.net...
"Mark D. Zacharias" <spammenot@nonsense.net> wrote in message
news:RmP%e.1$dB4.0@newssvr12.news.prodigy.com...

I just had a quick look at a few scrap lasers which were hanging around
the
workshop, and they have six connections to the

***** laser diode unit. *****

Looking
at a few schematics, these are one each for the anodes and cathodes of
the laser diodes ( one red, and one infra red for DVD and CD
respectively ) and one each for the feedback photo diode integrated with
each laser diode. The
snip

Just to be clear, I was referring to just the laser diode itself, not the
entire pickup.

Mark Z,

I do know the difference between a laser diode and an entire pickup, so I
was also referring to the laser diode, as I thought that I had carefully
explained, when I said that a typical one, used in a DVD player pickup,
has 6 connections, as opposed to one used in a CD only pickup, which has
only 3 connections. A complete pickup, either CD or DVD, has many more
connections, than 6.

A CD laser diode has two components in it - a laser diode and a feedback
diode, both integrated onto the same chip. A DVD laser diode, has the same
thing, but times two.

Arfa
Click to expand...
P.S.

I have a Panasonic DVD pickup at work which is disassembled to show to
customers. The actual diode is plainly visible, and has 3 legs soldered to a
small flex PC board.

Mark Z.
 
"Mark D. Zacharias" <spammenot@nonsense.net> wrote in message
news:DxW%e.8227$6e1.3058@newssvr14.news.prodigy.com...
"Arfa Daily" <arfa.daily@ntlworld.com> wrote in message
news:MCT%e.12292$0w.1516@newsfe5-gui.ntli.net...

"Mark D. Zacharias" <spammenot@nonsense.net> wrote in message
news:RmP%e.1$dB4.0@newssvr12.news.prodigy.com...

I just had a quick look at a few scrap lasers which were hanging around
the
workshop, and they have six connections to the

***** laser diode unit. *****

Looking
at a few schematics, these are one each for the anodes and cathodes of
the laser diodes ( one red, and one infra red for DVD and CD
respectively ) and one each for the feedback photo diode integrated
with each laser diode. The
snip

Just to be clear, I was referring to just the laser diode itself, not
the entire pickup.

Mark Z,

I do know the difference between a laser diode and an entire pickup, so I
was also referring to the laser diode, as I thought that I had carefully
explained, when I said that a typical one, used in a DVD player pickup,
has 6 connections, as opposed to one used in a CD only pickup, which has
only 3 connections. A complete pickup, either CD or DVD, has many more
connections, than 6.

A CD laser diode has two components in it - a laser diode and a feedback
diode, both integrated onto the same chip. A DVD laser diode, has the
same thing, but times two.

Arfa


P.S.

I have a Panasonic DVD pickup at work which is disassembled to show to
customers. The actual diode is plainly visible, and has 3 legs soldered to
a small flex PC board.

Mark Z.

Ok - Fair enough ! ;-)
Click to expand...

Arfa
 
You must log in or register to reply here.

Welcome to EDABoard.com

Sponsor

Back
Top