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 Disc Players and CDROM Drives

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مُساهمةموضوع: Disc Players and CDROM Drives    الأحد يوليو 25, 2010 12:35 am

Notes on the Troubleshooting and Repair of Compact Disc Players and CDROM
Drives
Version 3.53
Copyright ©[ندعوك للتسجيل في المنتدى أو التعريف بنفسك لمعاينة هذا الرابط]
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Sci.Electronics.Repair FAQ
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    Table of Contents
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مُساهمةموضوع: رد: Disc Players and CDROM Drives    الأحد يوليو 25, 2010 12:55 am

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مُساهمةموضوع: رد: Disc Players and CDROM Drives    الأحد يوليو 25, 2010 12:56 am

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مُساهمةموضوع: رد: Disc Players and CDROM Drives    الأحد يوليو 25, 2010 12:57 am


  1. Scope of this document

    This document was developed specifically for the troubleshooting and repair
    of the CD players in component stereo systems, compact stereos, boomboxes, car
    units and portables, as well as CDROM drives (including the Sony Playstation).
    The primary differences between these types will relate to how the disc is
    loaded - portables usually are top loaders without a loading drawer or tray:
    However, as a result of the level of miniaturization required for portables
    and to a lesser extent, CDROM drives, everything is tiny and most or all of
    the electrical components are surface mounted on both sides of an often
    inaccessible printed circuit board with the entire unit assembled using
    screws with a mind of their own and a desire to be lost.
    For other types:





  2. Laserdisc players and optical disk storage units have much in common
    with CD players with respect to the mechanical components and front-end
    electronics. Therefore, the information contained in this document can
    represent a starting point for their troubleshooting as well. However,
    they may include additional servo systems (optical pickup tilt, for
    example), as well as additional and/or different signal processing
    subsystems.

  3. DVD (Digital Versatile - or Video - Disc) players (which are now
    widely available and will completely replace CD players in a few years),
    suffer from many of the same problems as CDs and Laser Discs. Thus, a
    familiarity with the operating and repair of current technology will give
    you a head start on the amazing wonders (and similarly amazing problems) to
    come. There is a great deal of information on DVD technology in the
    DVD FAQ.
    Electronics Now, December, 1997, has a nice article by Steven J. Bigelow
    covering everything from the DVD format to installing and using a DVDROM
    drive in your PC.

  4. BD (Blu-Ray) players and recorders. Stay tuned for future developments.
    However, much of the information on CD and DVD technology applies to these
    next generation high capacity video and computer storage devices as well.
    Note that throughout this document, the term 'CD player' is used most often.
    However, it should be understood that in most cases, the information applies
    to CDROM drives, game machines using CDs like the Sony Playstation, laserdisc
    players, MiniDisk players/recorders, DVD players, and other types of optical
    disk systems. Also see the document specifically devoted to these other
    technologies: "
    Notes on the Troubleshooting and Repair
    of Optical Disc Players and Optical Data Storage Drives
    ". Also, where I
    remember, the term 'disc' is used to denote a read-only medium (e.g. a
    regular audio CD or LD) while 'disk' is used for one that is recordable
    (e.g., CD-R or MiniDisk).
    Note: Links to all the diagrams and photographs referenced from this document
    can be found in
    Sam's CD FAQ Files.

    Types of problems found in CD players

    Many common problems with CD players can be corrected without the need for
    the service manual or the use of sophisticated test equipment (though a
    reliable multimeter will be needed for any electrical tests and an oscilloacope
    of at least 5 MHz bandwidth is highly desireable for servo alignment and more
    advanced troubleshooting). The types of problems found in a CD player can be
    classified into several categories:
    Mechanical - dirt, lubrication, wear, deteriorated rubber parts, dirty/bad
    limit switches, physical damage. A dirty lens (coated with dust, tobacco
    smoke residue, or condensed cooking grease) - easily remedied - is probably
    the number one cause of many common problems: discs not being recognized,
    seek failure, audible noise, and erratic tracking, sticking, or skipping.
    Even many professionals may mistake (either accidentally or on purpose)
    these symptoms being due to much more serious (and expensive) faults.
    Don't be fooled!
    Cleaning of the lens and any other accessible optical components (usually
    only the turning mirror, if that) and a mechanical inspection should be the
    first things done for any of these problems (and as periodic preventive
    maintenance especially if the equipment is used in a less than ideal
    environment). See the section:
    General inspection,
    cleaning, and lubrication
    .



  5. Electrical Adjustments - coarse tracking, fine tracking, focus, laser
    power. However, some CD players no longer have some of these adjustments.
    The servo systems are totally digital - they either work or they don't.

  6. Power problems (mostly portables) - weak batteries, inadequate, defective,
    or improper AC wall adapter.

  7. Bad connections - broken solder on the pins of components that are stressed
    like limit or interlock switches, or audio or power jacks, internal
    connectors that need to be cleaned and reseated, broken traces on flexible
    cables, or circuit board damage due to a fall.

  8. Electrical Component Failure. These are rare except for power surge (storm
    and lightning strike) related damage which if you are lucky will only blow
    out components in the power supply. (Or, plugging a 3 V portable into the
    12 V of your automobile. You can probably forget about this even being a
    CD player again.)

  9. Incompatible geographic location. :-) This doesn't really apply to CD
    players but may be a factor with equipment like Sony PlayStations and
    very likely with DVD players. In their infinite wisdom (or greed),
    manufacturers are including 'country codes' on the discs so that a game
    or movie sold in one place cannot be used in another. So, if you bought
    a disc on the other side of the world and it doesn't work at home, thank
    the lawyers.....

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مُساهمةموضوع: رد: Disc Players and CDROM Drives    الأحد يوليو 25, 2010 12:58 am

You can often repair a CD player which is faulty due to (1) or (2) except
for laser power which I would not attempt except as a last resort without
a service manual and/or proper instrumentation if needed - improper adjustment
can ruin the laser. If discs are recognized at all or even if the unit only
focuses correctly, then laser power is probably ok. While the laser diodes
can and do fail, don't assume that every CD player problem is laser related.
In fact, only a small percentage (probably under 10%) are due to a failure
of the laser diode or its supporting circuitry. Mechanical problems such as
dirt and lubrication are most common followed by the need for electrical
(servo) adjustments.
The solutions to category (3) and (4) problems are obvious - but it may take
a conscious effort to remember to check these out before assuming that the
fault is due to something much more serious.
Category (5) failures in the power supply of component (AC line powered) CD
players can also be repaired fairly easily.
Most other electrical failures will be difficult to locate without the service
manual, test equipment, and a detailed understanding and familiarity with
audio CD technology. However, you might get lucky. I have successfully
repaired problems like a seek failure (replaced a driver chip because it was
running excessively hot) and a door sensor failure (traced circuitry to locate
a bad logic chip). Since so much of the intelligence of a CD player is in the
firmware - the program code inside the microcontroller, even the schematic may
be of only marginal value since I can pretty much guarantee that the firmware
will not be documented. The service manuals rarely explain *how* the equipment
is supposed to work - and then perhaps only in poorly translated Japanese!
You can pretty much forget about repairing electrical problems in portable
equipment other than perhaps bad connections (usually around the audio or
power jacks, internal connectors, interlock switch (since it is stressed), or
elsewhere due to the unit being dropped). Nearly everything in a portable
(and most CDROM drives for that matter though this is not quite as bad) is
itty-bitty surface mount components. There is generally only minimal useful
information printed on the circuit board. Tracing the wiring is a nightmare.
Even the test points and adjustments may be unmarked!

Repair or replace?



While CD players with new convenience features are constantly introduced, the
basic function of playing a CD has not changed significantly in 15 years.
None of the much hyped 'advancements' such as digital filters, oversampling,
one bit D/As, and such are likely to make any difference whatsoever in the
listening pleasure of most mortals. The people who care, do so only because
they are more concerned with the technology than the musical experience. Most
of these so called advances were done at least in part to reduce costs - not
necessarily to improve performance.
Therefore, unless you really do need a 250 disc CD changer with a
remote control that has more buttons than a B777 cockpit and 2000 track
programmability, a 10 year old CD player will sound just as good and
repair may not be a bad idea. Many older CD players are built more solidly
than those of today. Even some new high-end CD players may be built around
a mostly plastic optical deck and flimsy chassis.
If you need to send or take the CD player or CDROM drive to a service center,
the repair could easily exceed the cost of a new unit. Service centers
may charge up to $50 or more for providing an initial estimate of repair
costs but this will usually be credited toward the total cost of the repair
(of course, they may just jack this up to compensate for their bench time).
Parts costs are often grossly inflated as well - possibly due to a deliberate
effort on the part of manufacturers to discourage repair of older equipment.
However, these expensive parts do not really fail nearly as often as is
commonly believed - the laser is not the most likely component to be bad!
Despite this, you may find that even an 'authorized' repair center will want
to replace the expensive optical pickup even when this is not needed. I do
not know how much of this is due to dishonesty and how much to incompetence.
If you can do the repairs yourself, the equation changes dramatically as
your parts costs will be 1/2 to 1/4 of what a professional will charge
and of course your time is free. The educational aspects may also be
appealing. You will learn a lot in the process. Thus, it may make sense
to repair that bedraggled old boombox after all.



Back to
[ندعوك للتسجيل في المنتدى أو التعريف بنفسك لمعاينة هذا الرابط].
CD Digital Audio Technology


General Introduction to CD Technology



Information on a compact disc is encoded in minute 'pits' just under the
label side of the CD. The CD itself is stamped in much the same way as
an old style LP but under much more stringent conditions - similar to the
conditions maintained in the clean room of a semiconductor wafer fab. The CD
pressing is then aluminum coated in a vacuum chamber and the label side is
spin-coated with a protective plastic resin and printed with the label.
CD-Rs - recordable CDs use a slightly different construction. CD-R blanks
are prestamped with a spiral guide groove and then coated with an organic dye
layer followed by a gold film, resin, and label. The dye layer appears
greenish and deforms upon exposure to the focused writing laser beam to form
pits and lands.
The newest variation - DVDs or Digital Versatile Disks (or Digital Video
Disks depending on who you listen to) - implement a number of incremental
but very significant improvements in technology which in total add up to a
spectacular increase in information density - almost 10:1 for the same
size disc. These include higher frequency laser (670 or shorter visible
wavelength), closer track spacing, better encoding, and a double sided disc.
According to early reports on the final specifications, DVDs will be able
to store 8 times the audio of current CDs at a higher sampling rate and
bit resolution, 2 hours of MPEG encoded high quality movies, and
all kinds of other information. Raw data capacity is somewhere between
5 and 10 GBytes. See the section:
Comparison of CD
and DVD Specifications
for additional information.
On the near horizon is the "Blu-Ray" standard using a blue-violet laser
to achieve even higher capacity for multimedia and computer storage
applications. See the section:
Comparison of CD, DVD,
BD Specifications
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مُساهمةموضوع: رد: Disc Players and CDROM Drives    الأحد يوليو 25, 2010 12:59 am

CD information storage and playback



The actual information to be recorded on a CD undergoes a rather remarkable
transformation as it goes from raw audio (or digital data) to microscopic pits
on the disc's surface. For commercial or professional audio recording, the
process starts with pre-filtering to remove frequencies above about 20 kHz
followed by analog-to-digital conversion, usually at a sampling rate of 48 K
samples/second for each stereo channel. The resulting data stream is then
recorded on multi-track digital magnetic tape. All mixing and pre-mastering
operations are done at the same sampling rate. The final step is conversion
through re-sampling (sample-rate conversion including some sophisticated
interpolation) to the 44.1 K samples/second rate actually used on the CD (88.2
K total for both channels). (In some cases, all steps may be performed at the
44.1 K rate.)
That is followed by extremely sophisticated coding of the resulting 16-bit
two's-complement samples (alternating between L and R channels) for the
purpose of error detection and correction. Finally, the data is converted to a
form suitable for the recording medium by Eight-to-Fourteen modulation (EFM)
and then written on a master disk using a precision laser cutting lathe. A
series of electroplating, stripping, and reproduction steps then produce
multiple 'stampers', which are used to actually create the discs you put in
your player (more below).
Of course, it is possible to create your own CDs with a modestly priced CD-R
recorder (which does not allow erasing or re-recording). Now, re-writable CD
technology with fully reusable discs enables recording and editing to be done
more like that on a cassette tape
Like a phonograph record, the information is recorded in a continuous spiral.
However, with a CD, this track (groove or row of pits - not to be confused
with the selections on a music CD) starts near the center of the CD and
spirals (counterclockwise when viewed from the label side) toward the outer
edge. The readout is through the 1.2 mm polycarbonate disc substrate to
he aluminized information layer just beneath the label. The total length
of the spiral track for a 74 minute disc is over 5,000 meters - which is more
than 3 miles in something like 20,000 revolutions of the disc!
The digital encoding for error detection and correction is called the
Cross Interleave Reed-Solomon Code or CIRC. To describe this as
simply as possible, the CIRC code consists of two parts: interleaving
of data so that a dropout or damage will be spread over enough physical area
(hopefully) to be reconstructed and a CRC (Cyclic Redundancy Check) like error
correcting code. Taken together, these two techniques are capable of some
remarkable error correction. The assumption here is that most errors will
occur in bursts as a result of dust specs, scratches, imperfections such as
pinholes in the aluminum coating, etc. For example, the codes are powerful
enough to totally recover a burst error of greater than 4,000 consecutive
bits - about 2.5 mm on the disc. With full error correction implemented (this
is not always the case with every CD player), it is possible to put a piece
of 2 mm tape radially on the disc or drill a 2 mm hole in the disc and have no
audio degradation. Some test CDs have just this type of defect introduced
deliberately.
Two approaches are taken with uncorrectable errors: interpolation and
muting. If good samples surround bad ones, then linear or higher
order interpolation may be used to reconstruct them. If too much data has
been lost, the audio is smoothly muted for a fraction of a second. Depending
on where these errors occur in relation to the musical context, even these
drastic measures may be undetectable to the human ear.
Note that the error correction for CDROM formats is even more involved
than for CD audio as any bit error is unacceptable. This is one of many
reasons why it is generally impossible to convert an audio CD player into a
CDROM drive. However, since nearly all CDROM drives are capable of playing
music CDs, much can be determined about the nature of a problem by first
testing a CDROM drive with a music CD.

CD (disc) construction



The information layer as mentioned above utilizes 'pits' as the storage
mechanism. (Everything that is not a pit is called a 'land'.) Pits are
depressions less than 0.2 um in depth (1/4 wavelength of the 780 nm laser light
taking into consideration the actual wavelength inside the polycarbonate
plastic based on its index of refraction). Thus, the reflected beam is 180
degrees out of phase with incident beam. Where there is a pit, the reflected
beam from the pit and adjacent land will tend to cancel. This results in high
contrast between pits and lands and good signal to noise ratio. In the far
field (at the detector), the pit will appear dark and the land will appear
breight. Pits are about 0.5 um wide and they come in increments of 0.278 um
as the basic length of a bit (encoded, see below) on the information layer
of the disc.
Each byte of the processed information is converted into a 14 bit run length
limited code taken from a codebook (lookup table) such that there are no fewer
than 2 or more than 10 consecutive 0s between 1s. By then making the 1s
transitions from pit to land or land to pit, the minimum length of any feature
on the disc is no less than 3*p and no more than 11*p where p is 0.278 um.
This is called Eight-to-Fourteen Modulation - EFM. Thus the length of a pit
ranges from 0.833 to 3.054 um.
Each 14 bit code word has 3 additional sync and low frequency suppression bits
added for a total of 17 bits representing each 8 bit byte. Since a single bit
is 0.278 um, a byte is then represented in a linear space of 4.72 um. EFM in
conjunction with the sync bits assure that the average signal has no DC
component and that there are enough edges to reliably reconstruct the clock
for data readout. These words are combined into 588 bit frames. Each frame
contains 24 bytes of audio data (6 samples of L+R at 16 bits) and 8 bits of
information used to encode (across multiple frames) information like the time,
track, index, etc:
Sync (24 + 3).
Control and display (14 + 3).
Data (12 * 2 * (14 + 3).)
Error correction ( 4 * 2 * (14 + 3).)
--------------------
588 total bits/frame
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مُساهمةموضوع: رد: Disc Players and CDROM Drives    الأحد يوليو 25, 2010 1:00 am

A block, which is made up of 98 consecutive frames, is the smallest unit which
may be addressed on an audio CD and corresponds to a time of 1/75 of a second.
Two bits in the information byte are currently defined. These are called P
and Q. P serves a kind of global sync function indicating (among other
things) start and end of selections and time in between selections. Q bits
accumulated into one word made of a portion of the 98 possible bits in a block
encodes the time, track and index number, as well as many other possible
functions depending where on the disc it is located, what kind of disc this
is, and so forth.
Information on a CD is recorded at a Constant Linear Velocity - CLV. This is
both good and bad. For CD audio - 1X speed - this CLV is about 1.2 meters per
second. (It really isn't quite constant due to non constant coding packing
density and data buffering but varies between about 1.2 and 1.4 meters per
second). CLV permits packing the maximum possible information on a disc since
it is recorded at the highest density regardless of location. However, for
high speed access, particularly for CDROM drives, it means there is a need to
rapidly change the speed of rotation of the disc when seeking between inner
and outer tracks. Of course, there is no inherent reason why for CDROMs, the
speed could not be kept constant meaning that data transfer rate would be
higher for the outer tracks than the inner ones. Modern CDROM drives with
specs that sound too good to be true (and are) may run at constant angular
speed achieving their claimed transfer rate only for data near the outer edge
of the disc.
Note that unlike a turntable, the instantaneous speed of the spindle is not
what determines the pitch of the audio signal. There is extensive buffering
in RAM inside the player used both as a FIFO to smooth out data read off of
the disc to ease the burden on the spindle servo as well as to provide
temporary storage for intermediate results during decoding and error
correction. Pitch (in the music sense) is determined by the data readout
clock - a crystal oscillator usually which controls the D/A and LSI chipset
timing. The only way to adjust pitch is to vary this clock. Some high-end
players include a pitch adjustment. Since the precision of the playback of
the any CD player is determined by a high quality quartz oscillator, wow and
flutter - key measures of the quality of phonograph turntables - are so small
as to be undetectable. Ultimately, the sampling frequency of 44.1 K samples
per second determines the audio output. For this, the average bit rate from
the disc is 4.321 M bits per second.
Tracks are spaced 1.6 micrometers apart - a track pitch of 1.6 um. (This is
the nominal specification but may vary somewhat and will be less on those CDs
that contain more than 74 minutes of music or 650 MB of data. However,
unlike LPs, the pitch is not affected in the slightest by the content.) Thus
a 12 cm disc has over 20,000 tracks for its 74 minutes of music. Of course,
unlike a hard disk and like a phonograph record, it is really one spiral track
over 3 miles long! However, as noted above, the starting point is near the
center of the disc. The width of the pits on a track is actually about 0.5
um. The focused laser beam is less than 2 um at the pits. Compare this to
an LP: A long long playing LP might have a bit over 72 minutes of music on
two sides or 36 minutes per side. (Most do not achieve anywhere near this
much music since the groove spacing needs to vary depending on how much bass
content the music has and wide grooves occupy more space.) At 33-1/3 rpm,
this is just over 1,200 grooves in about 4 inches compared to 20,000 tracks
on a CD in a space of just over 1.25 inches! The readout stylus for an LP
has a tip radius of perhaps 2 to 3 mils (50 to 75 um).

CD (disc) manufacturing



(From: Reinhart (Lasernut23@aol.com).)
An LP is pressure pressed using a solid vinyl biscuit. A CD, on the other
hand, is not manufactured in this manner. CDs are replicated through
injection molding, where molten polycarbonate is injected into a mold under
high pressure. CDs *must* be manufactured in strict clean room environments.
On a side note, when LaserDiscs were released to market by MCA DiscoVision in
1978, this requirement wasn't recognized, or ignored by MCA Corporate in an
attempt to keep manufacturing costs of these silver platters down. The first
discs were manufactured in an environment similar to an LP plant. As a
result, the finished product, while looking visibly okay when observed
casually, had major problems playing reliably on many LaserDisc players.
Now, of course, we know better, although Pioneer recognized these requirements
far more quickly than MCA. Even RCA's Videodisc plant for their
needle-in-grove CED (SelectaVision Videodisc) format recognized these
requirements better than MCA! CED's market introduction in 1981 did not
start as catastrophically like LaserDisc did as a result.

And you thought driving on a narrow winding country road was tough!



To put the required CD player servo system performance into perspective, here
is an analogy:
At a constant linear velocity of about 1.2 meters per second, the required
tracking precision is astounding: Proper tracking of a CD is equivalent to
driving down a 10 foot wide highway (assuming an acceptable tracking error of
less than +/- 0.35 um) more than 3,200 miles for one second of play or over
14,400,000 miles for the entire disc without accidentally crossing lanes!
Actually, it is worse than this: focus must be maintained all this time to
better than 1 um as well (say, +/- 0.5 um). So, it is more like piloting a
aircraft down a 10 foot wide flight path at an altitude of about 12 miles (4
mm typical focal length objective lens) with an altitude error of less than
+/- 7 feet! All this while the target track below you is moving both
horizontally (CD and spindle runout of 0.35 mm) 1 mile and vertically (disc
warp and spindle wobble of up to 1 mm) 3 miles per revolution! In addition,
you are trying to ignore various types of garbage (smudges, fingerprints,
fibers, dust, etc.) below you which on this scale have mountain sized
dimensions. Sorry for the mixed units. My apologies to the rest of the world
where the proper units are used for everything).
The required precision is unbelievable but true using mass produced technology
that dates to the late 1970s. And, consider that a properly functioning CD
player is remarkably immune to small bumps and vibration - more so than an old
style turntable. All based on the reflection of a fraction of a mW of
invisible laser light!
Of course, this is just another day in the entertainment center for the CD
player's servo systems. Better hope that our technological skills are never
lost - a phonograph record can be played using the thorn from a rosebush using
a potter's wheel for a turntable. Just a bit more technology is needed to
read and interpret the contents of a CD!
And, for a DVD with its narrower longer track (0.74 um compared to 1.6 um
and more than twice as long), it's even more of a challenge!
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مُساهمةموضوع: رد: Disc Players and CDROM Drives    الأحد يوليو 25, 2010 1:01 am

Why does focus need to be so precise?



Since a laser printer doesn't need to have so precise a focus (afterall,
paper isn't that smooth), what's all this fuss about focusing with respect
to CD, DVD, and other optical disc/k systems? Laser beams remain fairly
parallel, no?
Wrong.
First, laser light that remains precisely parallel - doesn't diverge - only
can be found in bad Sci-Fi. Laser light still obeys the laws of physics and
in order to get the required spot size on the disc - about 1 micrometer (um),
1,000th of a mm, 1,000,000th of a meter, it needs to be focused precisely at
the disc surface. Due to manufacturing tolerances for disc flatness (warp),
the surface may move up-and-down as much as 100 times this amount. And disc
height from player to player isn't that precise either. Large diameter laser
beams can be kept quite parallel but a beam 1 um in diameter would diverge
at about a 60 degree angle. The lens in the CD player has a focal length of
about 4 mm and focuses the light from a beam a couple millimeters in diameter
to a 1 um spot on the disc surface and because of the small depth of focus,
the distance needs to be kept constant to 1 or 2 um. For DVD systems, the
required precision is even greater.
Laser printers DO have focusing optics with correction for the flat paper
surface. They don't need to be quite as precise because the spot size is
much larger than for a CD or DVD player - a 1,200 dpi printer would have a
spot on the order of 50 um. Therefore, the lens can be quite far away from
the paper and the depth of focus is much larger. Thus, no active focusing
mechanism is needed.

CD optical pickup operating principles



A diagram showing the major functional components of the three-beam optical
pickup described below is available in PDF format:
CDT3BP.
This design is typical of older optical pickups (though you may come across
some of these). Newer types have far fewer individual parts combining and
eliminating certain components without sacrificing performance (which may even
be better). Additional benefits result is lower cost, improved robustness,
and increased reliability. However, operating principles are similar.
The purpose of the optical pickup in a CD player, CDROM drive, or optical disk
drive, is to recover digital data from the encoded pits at the information
layer of the optical medium. (With recordable optical disks, it is also used
to write to the disk medium.) For CD players, the resulting datastream is
converted into high fidelity sound. For CDROMs or other optical storage
devices, it may be interpreted as program code, text, audio or video
multimedia, color photographs, or other types of digital data.
Most of the basic operating principles are similar for single-beam CD pickups
and for pickups used in other digital optical drives.
It is often stated that the laser beam in a CD player is like the stylus of a
phonograph turntable. While this is a true statement, the actual magnitude of
this achievement is usually overlooked. Consider that the phonograph stylus
is electromechanical. Stylus positioning - analogous to tracking and focus in
an optical pickup - is based on the stylus riding in the record's grooves
controlled by the suspension of the pickup cartridge and tone arm. The analog
audio is sensed most often by electromagnetic induction produced by the
stylus's minute movements wiggling a magnet within a pair of sense coils.
The optical pickup must perform all of these functions without any mechanical
assistance from the CD. It is guided only be a fraction of a mW of laser
light and a few milligrams of silicon based electronic circuitry.
Furthermore, the precision involved is easily more than 2 orders of magnitude
finer compared to a phonograph. Sophisticated servo systems maintain focus
and tracking to within a fraction of a micrometer of optimal. (1 um is equal
to 1/25,400 of an inch). Data is read out by detecting the difference in
depth of pits and lands of 1/4 wavelength of laser light (about 0.15 um in the
CD)!

  • The laser beam is generated by a solid state laser diode emitting at 780 nm
    (near IR). Optical power from the laser diode is no more than a couple of mW
    and exits in a wedge shaped beam with a typical divergence of 10x30 degrees
    in the X and Y directions respectively.
    Note that despite what some people believe, the laser diode in a CD or DVD
    player is a true laser and not just a glorified LED. It has a gain medium
    (the semiconductor), mirrors (on the cleaved parallel ends of the crystal),
    and an means of excitation (electric current). Its nearly monochromatic
    single spatial mode (TEM00) beam can be focused to a spot less than
    2 um in diameter. No LED or other non-laser light source is capable of
    this kind of performance.
  • A diffraction grating splits the beam into a main beam and two (first
    order) side beams. (The higher order beams are not used). Note that the
    diffraction grating is used to generate multiple beams, not for its more
    common function of splitting up light into its constituent colors. The
    side beams are used for tracking and straddle the track which is being read.
    The tracking servo maintains this centering by keeping the amplitude of the
    two return beams equalized.)
  • Next, the laser beam passes through a polarizing beam splitter (a type of
    prism or mirror which redirects the return beam to the photodiode array), a
    collimating lens, a quarter wave plate, a turning mirror, and the objective
    lens before finally reaching the disc.
  • The collimating lens converts the diverging beam from the laser into a
    parallel beam.
  • The quarter wave plate converts the linearly polarized beam into a
    circularly polarized beam. The purpose of this obscure step will become
    clear below.
  • A turning mirror (optional depending on the specific optical path used)
    then reflects the laser light up to the objective lens and focus/tracking
    actuators.
  • The objective lens is similar in many ways to a high quality microscope
    objective lens. It is mounted on a platform which provides for movement
    in two directions. The actuators operate similarly to the voice coils
    in loudspeakers. Fixed permanent magnets provide the magnetic fields
    which the coils act upon. The focus actuator moves the lens up and down.
    The tracking actuator moves the coil in and out with respect to the disc
    center.
  • The collimated laser beams (including the 2 side beams) pass through the
    objective lens and are focused to diffraction limited spots on the
    information - pits - layer of the disc (after passing through the 1.2
    millimeters of clear polycarbonate plastic which forms the bulk of the
    disc).
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عدد المساهمات : 34
تاريخ التسجيل : 16/06/2010

مُساهمةموضوع: رد: Disc Players and CDROM Drives    الأحد يوليو 25, 2010 1:02 am


  • The reflected beams retrace the original path back through the
    quarter wave plate and polarizing beam splitter. However, the reflected
    circularly polarized beam in passing through the quarter wave plate gets
    converted back into a linearly polarized beam but at an orientation
    90 degrees to the original!
    So, the polarizing beam splitter is able to
    divert it to the photodiode array. To repeat in different words: The
    polarizing beam splitter passes the (horizontally polarized) laser
    beams straight through. However, two passes (out and back) through
    the quarter wave plate rotates the polarization of the return beam
    to be vertical instead and it is reflected by the polarizing beam splitter
    toward the photodiode array. Sorry, an explaination of why quarter wave
    plates and polarized laser beams behave this way is somewhat beyond the scope
    of this document.

The return beams from the disc's information layer are used for servo control
of focus and tracking and for data recovery.

  • A cylindrical lens slightly alters the horizontal and vertical focal
    distances of the resulting spot on the photodiode array. The spot will then
    be perfectly circular only when the lens is positioned correctly. To close
    or to far and it will be elliptical (e.g., elongated on the 45 degree axis
    if too close but on the 135 degree axis if too far).
    The central part of the photodiode array is divided into 4 equal quadrants
    labeled A,B,C,D. Focus is perfect when the signal = (A+C)-(B+D) = 0.
    The actual implementation may use a thick beam splitter mirror (which adds
    astigmatism) or an astigmatic objective lens rather than a separate
    cylindrical lens to reduce cost but the effect is the same. Since the
    objective lens is molded plastic, it costs no more to mold an astigmat
    (though grinding the original molds may have been a treat!). It is even
    possible that in some cases, the natural astigmatism of the laser diode
    itself plays a part in this process.
  • The side beams created by the diffraction grating are positioned forward
    and back of the main beam straddling the track of pits being followed (not
    directly on either side as shown in the diagram - but that was easier to
    draw!).
    Segments on either side of the photodiode array designated E and F monitor
    the side beams. Tracking is perfect when the E and F signals are equal.
  • The data signal is the sum of A+B+C+D.

In essence, the optical pickup is an electronically steered and stabilized
microscope which is extracting information from tracks 1/20 the width of a
human red blood cell while flying along at a linear velocity of 1.2 meters
per second!
See the sections: "Parts of a CD Player or CDROM Drive" and "Startup Problems"
for more information on the components and operation of the optical pickup and
descriptions and photos of some typical laser diodes, optical pickups, and
optical decks.
The Laser
Fundamentals Page has an interactive tutorial (requires JAVA) illustrating
the operation of an optical pickup in very simplified form. It doesn't really
have much detail but if the explanation above makes no sense, it may be worth
viewing.

Optical pickup complexity



The opto-mechanical design of optical pickups varies widely. Originally, they
were quite complex, bulky, heavy, and finicky with respect to optical
alignment. However, in their continuing effort to improve the design, reduce
the size and mass, and cut costs, the manufacturers have produced modern
pickups with remarkably few distinct parts. This should also result in better
performance since each optical surface adds reflections and degrades the the
beam quality. Therefore, the required laser power should be reduced and the
signal quality should improve.


  • Generally, the most complex types are also the oldest. With these, there
    were individual optical elements for each stage in the beam path and
    completely separate laser diode and photodiode array packages. In short,
    while details varied, the overall construction was very similar to the
    diagram and description given in the section: CD optical
    pickup operating principles
    . These also had several optical adjustments
    - which in some cases needed frequent attention.
    An example of this type is the Sony KSS110C Optical
    Pickup. Most components perform individual functions and it is larger
    and heavier than more modern designs.
  • The most common types still have a separate laser diode and photodiode
    array but may have eliminated the cylindrical and collimating lenses and
    perhaps the polarizer and quarter wave plate. There are few if any
    adjustments.
    The Sony KSS361A Optical Pickup is typical of
    these mainstream designs. With very minor variations (mostly in mounting),
    various models may be found in all types of CD players and CDROM drives
    manufactured by Sony, Aiwa, and others.
    Another similar design is used in the Sanyo K38N Optical
    Pickup which is somewhat newer and more compact.
    For a diagram and detailed description of these mainstream pickups, see the
    section: [ندعوك للتسجيل في المنتدى أو التعريف بنفسك لمعاينة هذا الرابط].
  • Some manufacturers have gone to a combined laser diode/photodiode (LD/PD)
    array package which looks like a large LD but with 8 to 10 pins. Aside from
    the objective lens assembly, the only other part may be the turning mirror,
    and even this is really not needed. Such a pickup can be very light in
    weight (which is good for fast-access drives) and extremely compact.
    Eliminating the components needed to separate the outgoing and return beams
    should result in substantial improvement in optical performance. The only
    disadvantage would be that the beams are no longer perfectly perpendicular
    to the disc 'pits' surface and this may result in a very slight, probably
    negligible reduction in detected signal quality - more than made up for by
    the increased signal level.
    The CMKS-81X Optical Pickup and
    Optical Pickup from Philips PCA80SC CDROM
    are typical of these modern designs.
    The smallest ones such as the Optical Pickup from the
    Philips CR-206 CDROM are only about 1/2" x 5/8" x 3/4" overall - just
    about the size of the lens cover! For this single-beam pickup, there are
    absolutely NO additional optical elements inside. A three-beam pickup would
    have a diffraction grating in front of the laser diode.
    Some of these use what are known as "hologram lasers" (a designation perhaps
    coined by Sharp Corporation). With
    these, the functions previously performed by multiple optical components.
    can be done by a "Holographic Optical Element" or HOE. The HOE can simply
    be a diffraction grating replacement or can be designed to perform some more
    complex beam forming. A variety of hologram lasers (as well as conventional
    laser diodes and photodiode arrays) are listed under
    Sharp Laser
    Diode Products. The typical Sharp hologram laser (versions for CD, DVD,
    and other types of optical storage devices) eliminate the normal diffraction
    grating in the three-beam pickup as well as the polarizing beam splitter and
    associated components making for a very simple, compact, low cost unit.
    DVD Laser Holographic Optical Element
    shows the HOE glued to the front of a DVD laser diode assembly.
    For a diagram and detailed description of this type of pickup, see the
    section: [ندعوك للتسجيل في المنتدى أو التعريف بنفسك لمعاينة هذا الرابط].
الرجوع الى أعلى الصفحة اذهب الى الأسفل
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عدد المساهمات : 34
تاريخ التسجيل : 16/06/2010

مُساهمةموضوع: رد: Disc Players and CDROM Drives    الأحد يوليو 25, 2010 1:03 am

For more information on CD technology



The books listed in the section: [ندعوك للتسجيل في المنتدى أو التعريف بنفسك لمعاينة هذا الرابط]
include additional information on the theory and implementation of digital
audio, laserdisc, and optical drive technology.
Philips/Magnavox used to have a very nice on-line introduction to a variety
of consumer electronics technologies. Although their site has disappeared -
and even people who work for them have no clue - I have now recovered
several of the articles including those on TVs, VCRs, camcorders, satellite
reception, and connections. See the Introductory Consumer Electronics
Technology Series.
Also check out:

  • A
    Fundamental Introduction to the Compact Disc Player is a somewhat more
    theoretical discussion of compact disc audio technology with diagrams and
    even some equations. If it doesn't put you to sleep, you will find quite a
    bit of interesting information in this article. In either case, it may prove
    of value.
  • The University of Washington has at least one course in consumer
    electronics which varies from year to year. Last year (2000) it was on
    CD technology but most of that info has disappeared. However, there is
    an on-line tutorials which appears to be an excellent resource providing
    easy to understand discussions with many diagrams:

    • Audio
      Compact Disc - An Introduction.


  • The How Stuff Works Web
    site has some really nice introductory material (with graphics) on a variety
    of topics relating to technology in the modern world. Of relevance to this
    document are articles on CD technology, motors, remote controls, power
    adapters, etc.
  • The Cimram International, Inc Web
    site has some information on CD and DVD technology, formats, mastering, and
    manufacturing.

The following sites have a variety of information on CD and DVD technology:

  • CD Page
  • MediaWorld

A site with CD-R specific information including some repair tips is:

  • Andy McFadden's CD-R FAQ.

An extensive amount of information on other optical disc/k technologies with
many useful links can be found at:

  • Leopold's Audio/Video Page
  • MiniDisc, DAT, CD-R,
    DVD-RAM, etc..
  • The DVD Page.
  • DVD Central at E/Town.
  • DVD Demystified (Includes the
    DVD FAQ).




Back to [ندعوك للتسجيل في المنتدى أو التعريف بنفسك لمعاينة هذا الرابط].
CD Player Placement, Preventive Maintenance, and CD Care


General CD player placement considerations



Proper care of a CD player does not require much. Following the
recommendations below will assure peak performance and long life, and
minimize repairs.

  • Locate the CD player in a cool location. While the CD player is not
    a significant heat producer, keeping it cool will reduce wear and
    tear on the internal components and assure a long trouble free life.
  • Don't locate CD players in dusty locations or areas of high (tobacco)
    smoke or cooking grease vapors. I cannot force you to quit smoking,
    but it is amazing how much disgusting difficult to remove brown grime
    is deposited on sensitive electronic equipment in short order from
    this habit.
  • Make sure all audio connections are tight and secure to minimize
    intermittent or noisy sound.
  • Finally, store CDs away from heat. The polycarbonate plastic used to
    mold CDs is quite sturdy but high temperatures will eventually take
    their toll. Return them to their jewel cases or other protective
    container when not being played.


Preventive maintenance



You no doubt have heard that a CD should be cleaned and checked periodically.
"Purchase our extended warranty" says the salesperson "because CD players
are very delicate and require periodic alignment". For the most part, this
is nonsense. CD players, despite the astonishing precision of the optical
pickup are remarkably robust. Optical alignment is virtually never needed
for a component CD player and is rarely required even for portable or
automotive units. In fact, modern CD players often don't even have any of
these adjustments - the components of the optical pickup are aligned at the
factory and then fixed in place with hardening sealer.
An occasional internal inspection and cleaning is not a bad idea but not
nearly as important as for a VCR. Realistically, you are not going to do
any of this anyway. So, sit back and enjoy the music but be aware of the
types of symptoms that would be indications of the need for cleaning or other
preventive or corrective maintenance - erratic loading, need to convince the
CD player to cooperate and play a disc, audio noise, skipping, sticking, and
taking longer than usual to recognize a disc or complete a search.
If you follow the instructions in the section: A HREF="#cdgicl">General
inspection, cleaning, and lubrication, there is minimal risk to the
CD player. However, don't go overboard. If any belts are in good condition
(by appearance and stretch test), just clean them or leave them alone. Except
for the Sony drawer loading mechanism, belts are rarely as much of a problem
in CD players as in VCRs.
Of course, acute symptoms like refusal to play or open the door is a sign
of the need for emergency treatment. This still may mean that a thorough
cleaning is all that is needed.
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عدد المساهمات : 34
تاريخ التسجيل : 16/06/2010

مُساهمةموضوع: رد: Disc Players and CDROM Drives    الأحد يوليو 25, 2010 1:04 am

CD lens cleaning discs



Every CD, stereo equipment, department, discount, store - and even sidewalk
venders - carries CD lens cleaning discs. Are they of any value? Can they
cause damage?
I generally don't consider CD lens cleaning discs to be of much value for
preventive maintenance since they may just move the crud around. However,
for pure non-greasy dust (no tobacco smoke and no cooking grease), they
may not hurt and could even do a good enough job to put off a proper
cleaning for a while longer.
However, it's also possible they will ruin the lens. Consider that the worst
thing to do to a precision optical surface is to wipe it with a dry cloth as
this is likely to scratch the surface as it rubs the dust over it. To the
lens, a speck of dust is like a boulder. Once the lens is scratched,
replacement of the entire optical pickup is the only remedy. And, since
there are absolutely no sorts of standards for these things, it is possible
for a really poorly designed cleaning disc to damage the lens even if the
dust itself is non-abrasive. In addition, if the cleaning disc doesn't look
like a CD to the optical pickup or disc-in sensor, the lens it may not even
spin. So, the drawer closes, the drawer opens, and NOTHING has been
accomplished! (But at least no damage will be done.)
As if this isn't enough, NEVER put one into a high-X CDROM (DVD player or
DVDROM drive). The high speed rotation may cause the cleaning disc and/or
player/drive to self destruct. And, don't try a cleaning disc on an
automotive CD player that sucks in the disk - it will get stuck.

CD protection and handling



Although CDs are considerably more tolerant of abuse than LPs, some
precautions are still needed to assure long life. Also, despite the
fact that only one side is played, serious damage to either side can
cause problems during play or render the CD totally useless.
It is important that the label side be protected from major scratches which
could penetrate to the information layer. Even with the sophisticated
error correction used on the CD, damage to this layer, especially
if it runs parallel to the tracks, can make the CD unusable.
The CD is read by focusing a laser beam through the bottom 1.2 mm of
polycarbonate. As a result of the design of the optical system used in the
pickup, at the bottom surface, the beam diameter is about 1 mm and thus small
scratches appear out of focus and in many cases are ignored and do not cause
problems.
At the information layer with the pits, the beam diameter has been reduced
to under 2 um. Still, scratches running parallel to the tracks are more
problematic and can cause the optical pickup to get stuck repeating a track,
jumping forward or back a few seconds, or creating noise or other problems
on readout. In severe cases, the CD may be unusable especially if the
damage is in the directory area.
This is why the recommended procedure for cleaning a CD is to use soap and
water (no harsh solvents which may damage the polycarbonate or resin overcoat)
and clean in a radial direction (center to edge, NOT in the direction of the
tracks as you would with an LP). While on the subject of CD care, CDs should
always be returned to their original container for storage and not left out
on the counter where they may be scratched. However, if there is a need to
put one down for a moment, here are some considerations:

  • The label side is probably to be preferred since minor scratches have no
    effect on performance as long as they do not penetrate to the storage layer
    below (in which case the CD is probably history). Protectors are available
    to prevent damage to the label side of the disc. Personally, I think this
    is taking care to an excessive level but, hey, if you use your CDs as
    frisbies, go for it!
  • However, the opposite argument may apply as well: Slight damage to the
    readout-side will be ignored by the optical system or corrected for by the
    decoding process And, there are ways of dealing with scratches should they
    occur.

Thus, I won't offer a hard and fast rule other than to avoid leaving CDs out
where the dog can get to them. Smile
Never apply sticky labels to the readout-side of a CD or to the label-side
unless they are specifically designed for this application. And, if a label
was stuck on despite the warnings, don't attempt to remove it (or at least
exercise the utmost care) as the lacquer layer and some of your valuable bits
may come away with it. This is especially critical for CD-Rs (and maybe
CD-RWs) which seem to be more fragile than normal CDs. I've seen samples
of CD-Rs literally self destruct due to slight stress on the label side.

CD cleaning



You do not need a fancy CD cleaning machine.
Use a soft cloth, tissue, or paper towel moistened with water and mild
detergent if needed. Wipe from center to edge - NOT in a circular motion
as recommended for an LP. NEVER use any strong solvents. Even stubborn
spots will eventually yield to your persistence. Washing under running
water is fine as well.
Gently dry with a lint free cloth. Do not rub or use a dry cloth to clean
as any dirt particles will result in scratches. Polycarbonate is tough
but don't expect it to survive everything. Very fine scratches are not
usually a problem, but why press your luck?

Should I really worry about cleaning my CDs?



Something that not everyone is aware of is the multilevel error handling
technology in a CD player. Therefore, a dirty CD may not produce instantly
obvious audio problems but can nonetheless result in less than optimal
audio performance.
Very severe errors - long bursts - will result in audible degradation
including noise and/or muting of the sound. Even this may not always be
detectable depending on musical context.
Shorter runs of errors will result in the player interpolating between
what it thinks are good samples. This isn't perfect but will probably not
be detected upon casual listening.
Errors within the correcting capability of the CIRC code will result in
perfect reconstruction.
Not all players implement all possible error handling strategies.
Therefore, it is quite possible for CD cleaning to result in better
sound. However, a CD that is obviously clean will not benefit and
excessive cleaning or improper cleaning will introduce fine (or not so
fine) scratches which can eventually cause problems.
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عدد المساهمات : 34
تاريخ التسجيل : 16/06/2010

مُساهمةموضوع: رد: Disc Players and CDROM Drives    الأحد يوليو 25, 2010 1:11 am

Can a dirty CD or dirty lens damage my player?



So the droid in the CD store warned you that dirty CDs could do irepairable
harm to your CD player, your stereo, your disposition, etc. "Buy our $19.95
Super-Laseriffic CD cleaning kit".
The claim made at one major chain was that dirt or dust on the laser eye would
cause heat build-up that would burn out the mechanism. This is different
from a dirty disc. The cleaner he was pushing was a little brush attached to
a CD that brushed off the lens as it played.
This is total rubbish. The power of a CD laser is less than 1 mW and is not
concentrated at the lens. And, as noted elsewhere, those cleaning CDs with
the little brush are next to useless on anything but the smallest amount of
dry dust.
There are a lot of suckers out there. Save your money.
The worst that can happen is the CD will not play properly. There may be
audible noise, it may fail to track properly, abort at random times, or not
even be recognized. The electronics will not melt down.
It is just about impossible for a dirty CD to do any damage to the player.
A dirty lens will only result in disc recognition or play problems similar
to those caused by a dirty CD. The laser will not catch fire.
The only way damage could occur is if you loaded a cracked CD and the crack
caught on the lens.
You do not need any fancy CD cleaners in any case - soap or mild detergent
and water and a soft cloth are all that are required. If the CD looks clean,
it probably will be fine. If there are serious smudges or fingerprints,
then cleaning could make a significant difference in performance.
For further information, see the sections "CD cleaning" and "General
inspection, cleaning, and lubrication".

Rental or library CD considerations



Unlike old or worn video tapes, it is unlikely that a 'bad' CD could damage
your player. If the borrowed CD is dirty, clean it as described in the
section: [ندعوك للتسجيل في المنتدى أو التعريف بنفسك لمعاينة هذا الرابط]. If it is badly scratched,
the worst that will happen is that it will sound bad - skipping and audible
noise. No damage to your player will result. However, if the CD is cracked
or broken (this is really difficult to do but I have gotten cracked CDs from
public libraries), don't even attempt to load it - a broken edge could catch
on the lens and ruin the optical pickup entirely. An improperly made or
defective CD could result in seek/search problems which could eventually
overheat and/or damage components but you'd probably notice the lack of music
before anything irreversible happened.
(From: Bart Wessel (wessel@home.nl).)
There seems to be a new risk in playing CDs or CD-ROMs borrowed from a
public library.
New, because of the fact that (at least at our library) they have a small
metallic strip attached to the top of the CD, apparently as a measure
against theft. The strip can be activated/deactivated at the counter, just
like the system in use in most department stores.
The risk comes from the fact that these strips can come off if you happen
to have a CD-ROM player that plays at speeds higher than 40X. There
is a warning on the box not to use plates over 40X but who reads the
warnings!

Can a CD player damage CDs?



The perhaps unexpected answer is a definite *yes* even though everyone has
heard about the virtues of non-contact laser playback. There are several
ways that a broken or poorly designed or manufactured player can result in
scratched discs:

  • If the lens moves too high while attempting to focus and the mechanical
    stop does not prevent it from hitting the disc, scratches can occur. On
    some players, the objective lens can easily go this high if focus is not
    found on the first pass. Note that in most cases, the lens will not suffer
    since it is protected by a raised ridge which is what actually scratches
    the disc.
  • Mechanical misalignment of the spindle motor or plastic cabinet parts can
    result in the disc touching the bottom or top of the disc compartment and
    this can leave scratches. This could be the result of poor or cheap design,
    shoddy manufacturing, or damage from a fall or other abuse.
  • If the control logic gets confused, it may allow you to eject a disc while
    it is still spinning and not fully supported by the spindle platter. A
    dirty disc that resulted in failure of the CLV servo to lock can result in
    a disc speed runaway condition with some players. If the drawer is then
    opened too soon, the disc will still be spinning because the controller has
    no way of knowing its present status and will not have provided enough
    reverse torque to stop the spindle motor - or too much and it will be
    spinning in reverse.

The likelihood of any of these is increased with dirty, smudged, warped, or
previously damaged discs.
Minor scratches may not result in a serious problem and there are products
to polish them - don't know how well they work. However, if these scratches
can be proven to be a direct consequence of a defective player still under
warranty, you should try to get some compensation from the manufacturer for
any seriously damaged and now unplayable CDs.
The one thing that is extremely unlikely is that the laser beam itself is
damaging the disc. Although this IS in principle possible IF the disc is
stationary AND the laser is on and focussed properly, AND laser power were
high enough, at most what would happen is that the information layer would
have a microscopic hole blown in it (and this would be taken care of by the
error correction processing). However, this really is extremely improbable
in a normal CD player or CDROM drive with normal CDs, especially if the unit
is working otherwise since the disc starts spinning as soon as focus is
established. Forget it. Mechanical causes of damaged discs are about a
zillion times more likely! :-)
Thus, there is absolutely no way for a software command to the CDROM drive
to affect the contents of the disc in any way. The laser power is simply
too low to affect the CD and there is no way to boost it, even for an instant.
Anything you've heard to the contrary it total rubbish. However, a faulty
CD-R or CD-R/W writer could indeed result in damage to CD-R and CD-R/W media
from its higher power laser but that's another story.
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مُساهمةموضوع: رد: Disc Players and CDROM Drives    الأحد يوليو 25, 2010 1:12 am

Repairing a scratched CD



So your five year old decided that your favorite CD would make nice
frisbee - didn't really know much about aerodynamics, did he?
Now it sounds like a poor excuse for a 78 rpm record. What to do?
There seem to be about as many ways of fixing scratches on CDs as producing
them in the first place. However, they fall into 3 classes of techniques:

  1. Mild abrasives: plastic or furniture polish, silver polish, toothpaste.
    These will totally remove minor scratches. DO NOT use anything that contains
    solvents including petrolium distillates - if it smells like kerosene, it
    will likely attack the polycarbonate plastic of the CD rendering it useless.
    Brasso(tm), a popular product may fall into this category but I've
    also heard that it works fine without damaging the CD.
  2. Fillers: turtle wax, car wax, furniture wax. Apply over the whole disc
    and buff out with a lint free cloth. Filling larger scratches should
    be fairly effective but the disc will be more prone to damage in the
    future due to the soft wax.
  3. Motorized buffing wheel. Sort of a miniature version of what is used
    for polishing your car. Smile See the details below.
  4. Blowtorch. At least one person who claims to have worked for several years
    in used CD store swears by this technique. Supposedly, he uses a pencil-type
    pocket butane torch and with great dexterity fuses the surface layer of the
    readout side of the disc so that all of those scratches and unsightly
    blemishes-well-melt away. Obviously, there are dangers in using fire on
    plastic and this is likely a last resort. I would assume that you are
    rolling with hysterical laughter at this point. In any case, I would not
    take this approach too seriously :-).

For (1) and (2), as with cleaning a CD, when applying or rubbing any of these
materials, wipe from the center to the outside edge. A CD player can
generally track across scratches that are perpendicular to its path reasonable
well, but not those that run the parallel to the tracks.
A mild abrasive will actually remove the scratch entirely if it is minor
enough. This is probably more effective where the surface has been scuffed
or abraded rather than deeply scratched.
Wax-like materials will fill in the space where the scratch is if the
abrasive was not successful. Even deep scratches may succumb to this
approach.
A combination of (1) and (2) may be most effective.
Exorbitantly priced versions of these materials are available specifically
marketed for repair of CDs. However, the common abrasives and waxes should
work about as well.
I cannot comment on the use of the blowtorch or how many years of practice is
required to get you CD repair license with this technique. However, I am
highly skeptical that this works at all and suspect that destruction of the CD
is the most likely outcome - totally melting, warping, or cracking or
shattering from the thermal stress. In other words, I don't recommend trying
the Blowtorch approach unless you have a stack of AOL or MSN CDs to sacrifice
and you have sufficient accident insurance!
Even some of other solutions may make the problem worse or destroy the CD
entirely if not done correctly or if the wrong materials or technique is
used. So, test any method on a CD you don't care about first.
An alternative to CD home repair are companies specializing in this service.
A couple of these are: Aural Tech
CD and CD Repairman. I do not
have information as to their effectiveness or cost. However, if you have a
very special irreplaceable CD that someone used as a skateboard, one of these
may be worth considering.
(From: Shawn Stopper (shstop@prodigy.net).)
In the CD repair process, I use a 1/4 horse electric motor, cotton buff, 2
hose clamps, 2 washers, a screw, and brown tripoli rouge. The motor should
be mounted to a surface for permanent use. The first hose clamp should be
mounted about halfway back on the motor shaft. A shaft about 4 inches in
length will be necessary for this application. after mounting the first
hose clamp, apply a washer, the buff, another washer, and the final hose
clamp. Mount a screw about 1/2 inch above the motor shaft where the outer
clamp can be twisted around the screw to keep the buff spinning. When
buffing cds, start out using brown tripoli rouge and slowly move the cd from
inside to out. Do not apply too much pressure on the CD because this will
cause the CD to "splinter", and it will be ruined. Patience is the key to
CD buffing. The first few you do may take longer than you expect, but the
more you do the better you get at it. At this time, I can buff about 3 to 4
CDs in five minutes. Once again, practice is the key!
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مُساهمةموضوع: رد: Disc Players and CDROM Drives    الأحد يوليو 25, 2010 1:13 am

Repairing top-side problems on CDs



If scratches penetrate to the information layer, all bets may be off. Much
of the optical system compliance with respect to damage depends on the short
depth of focus assuring that surface scratches *on the bottom* will be out
of focus and ignored. This is not possible with damage to the pits. Even
though the CIRC code should be able to deal with thousands of bad bits, such
damage can confuse the tracking servos to the point where the disc will be
unusable.
What if the aluminum (or gold) reflective layer has come off with no damage
to the plastic underneath? First of all, I don't know how this could occur
unless you were attempting to clean them with a strong solvent. Any physical
damage which removed the mirror coating will also damage the pits and recoating
will be useless.
(Note that I have unintentionally removed the gold coating on a CD-R using a
solvent similar to what is in Liquid Wrench(tm). I was actually trying to
remove the label but went a little too far! The solvent apparently dissolved
the greenish coating or binding underneath allowing the gold film and label
to just flake off - very strange behavior. Most of the green layer was still
intact. I now have a nice greenish somewhat transparent plastic coaster.)
Some discs may still work on some players or drives without the aluminum
coating. However, this isn't that likely. How to replace it? Ideally,
vacuum deposition is needed. The problem isn't only the reflectance but
the micro structure - the original coating was vacuum deposited to conform
to the pits and lands of the information layer. It is perfectly uniform below
the resolution of the laser beam. Modeling (silver or gold colored) paint is
amorphous and rough at these feature sizes and floppy disk write protect
stickers or other adhesive backed reflective films don't even come close
to contacting the information layer consistently. Mirror paint may work
but is a long-shot.



Back to [ندعوك للتسجيل في المنتدى أو التعريف بنفسك لمعاينة هذا الرابط].
CD Player and CDROM Drive Troubleshooting


SAFETY



While there are far fewer potential dangers involved in servicing a CD or DVD
player compared to a TV, monitor, or microwave oven, some minimal precautions
are still required when working with the cover removed. These relate to
electrical connections to the AC line and exposure to the laser beam:

  • Electrical: There may be a few exposed electrically live parts from the
    power line, usually around the power cord entrance, power transformer,
    and on/off switch. If there are, tape them over or cover them somehow
    so you need not be concerned with a low tech shock! Unless you are
    troubleshooting a primary side power supply problem, there will be no
    need to go near the AC line.
  • Laser (CD): The laser in a CD player is infra red, near IR - 780 nm -
    border of visible range but for all intents and purposes invisible. However,
    it is very low power (generally under 1 mW at the lens) and due to the optics,
    extremely unlikely that you could be in any danger. Nonetheless, don't
    go out of your way to look closely into the lens while the unit is on!
    As long as the lens is intact, the beam is highly divergent and at anything
    beyond a few inches, especially at an oblique angle, is quite safe. The
    only possibility of risk would be if the lens fell out and you were looking
    directly into a collimated beam from above. While the power is less than
    that of most laser pointers, there would be no aversion reflex to the nearly
    invisible IR. And, yes, some models of CD players are known to drop their
    lenses!
    CAUTION: There is usually a very low intensity (in appearance) emission
    from an IR laser which appears deep red. It will be visible as a spot the
    size of the period at the end of this sentence when the lens is viewed from
    an oblique angle. For a photo of how it actually looks in the dark, see
    Appearance of IR (780 nm) Laser in CD Pickup
    (Original photos courtesy of Gag Helfront (ie.dunster@ukonline.co.u).)
    This is just your eye's response to the near IR energy of
    the main beam. (Some people apparently cannot see this at all.) Do not be
    mislead into thinking that the laser is weak as a result of how dim this is.
    The main beam is up to 10,000 times more intense than it appears! It's
    power output is generally around 1 mW - comparable to a laser pointer. Take
    care. However, the red dot is an indication that the laser is being powered
    and probably functional, though it is no guarantee of the latter. You really
    need a laser power meter or at least an IR detector to confirm the existence
    of an IR laser beam.
    Whenever a full size (5-1/4") CD is in place, there is absolutely no danger
    of exposure to the laser beam. Reflections of laser light at these power
    levels are harmless. However, if you are testing with a 3-1/2" 'single' or
    homemade cut-down test CD (see the section: Useful ways
    to mangle CDs
    , avoid staring into the lens if there is any chance the
    laser is powered.
    If you don't want to take even the minimal risk of looking into the lens at
    all, project the beam onto a piece of paper held close to the lens. In a
    dark room, it should be possible to detect a red spot on the paper when the
    laser is powered.
  • Laser (CD-R, CD-RW, and other writeable optical drives): These may use IR
    laser diodes producing 10s of mW. A typical CD-R drive sets the laser power
    at 3 to 5 mW for read and 25 to 30 mW for write. While the basic precautions
    are the same, much greater care must be taken due to the much higher power
    when writing.
  • Laser (DVD): The DVD laser pickup is very similar to that of the CD player
    except that the wavelength is in the 635 to 650 nm range which is a very
    visible red - about the same as the color of newer laser pointers or a
    helium-neon laser (632.6 nm). The power is still under 1 mW and everything
    else above is still applicable.
    One note: If the DVD player is of the dual pickup variety with a separate
    laser for CDs, that one is IR like a normal CD player and the precautions
    listed above will apply. Take care because it may not be obvious ahead of
    time which one (or if both) will be powered!
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مُساهمةموضوع: رد: Disc Players and CDROM Drives    الأحد يوليو 25, 2010 1:14 am

Troubleshooting tips



Many problems have simple solutions. Don't immediately assume that
your problem is some combination of esoteric complex convoluted
failures. For a CD player, it may just be a bad belt or dirty lens.
Try to remember that the problems with the most catastrophic impact on
operation (a CD player that will not play past track 6) usually have
the simplest solutions (the gears that move the optical pickup need
lubrication). The kinds of problems that we would like to avoid at all
costs are the ones that are intermittent or difficult to reproduce: the
occasional audio noise or skipping or a CD player that refuses to play
classical CDs (depending on your tastes!) of music composed between the
years 1840 and 1910.
When attempting to diagnose problems with a CDROM drive, start by trying
to get it to play an audio CD. Data readback is more critical since
the error correction needs to be perfect. However, with audio playback
functional, all of the optical pickup and most of the servo systems and
front-end electronics must be working. A CDROM drive which cannot even
play a music CD will have no chance of loading Windows 95.
If you get stuck, sleep on it. Sometimes, just letting the problem
bounce around in your head will lead to a different more successful
approach or solution. Don't work when you are really tired - it is both
dangerous and mostly non-productive (or possibly destructive).
Whenever working on precision equipment, make copious notes and diagrams.
You will be eternally grateful when the time comes to reassemble the unit.
Most connectors are keyed against incorrect insertion or interchange
of cables, but not always. Apparently identical screws may be of differing
lengths or have slightly different thread types. Little parts may fit in
more than one place or orientation. Etc. Etc.
Pill bottles, film canisters, and plastic ice cube trays come in handy for
sorting and storing screws and other small parts after disassembly.
Select a work area which is well lighted and where dropped parts can
be located - not on a deep pile shag rug. Something like a large plastic
tray with a slight lip may come in handy as it prevents small parts from
rolling off of the work table. The best location will also be relatively
dust free and allow you to suspend your troubleshooting to eat or sleep or
think without having to pile everything into a cardboard box for storage.
Another consideration is ESD - Electro-Static Discharge. The electronic
components - especially the laser diode - in CD players, CDROM drives, and
similar devices, are vulnerable to ESD. There is no need to go overboard but
do take reasonable precautions like not wearing clothing made of wool that
tends to generate static. When working on component CD and laserdisc players,
get into the habit of touching a ground like the metal chassis before touching
any circuit components. The use of an antistatic wrist strap would be further
insurance especially if the optical pickup assembly needs to be unplugged for
any reason.
A basic set of precision hand tools will be all you need to disassemble
a CD player and perform most adjustments. However, these do not need to be
expensive. Needed tools include a selection of Philips and straight blade
screwdrivers, needlenose pliers, wire cutters, tweezers, and dental picks.
A jeweler's screwdriver set is a must particularly if you are working on
a portable CD player or CDROM drive.
For making servo adjustments, non-metallic fine tip jeweler's screwdrivers
or alignment tools will be essential as some of the front-end circuitry may
be sensitive to body capacitance - contact with the slot may alter the
behavior of the player (for better or for worse). In a pinch, wrapping
electrical tape around the part of a normal jeweler's that you grasp will
probably provide enough isolation. However, with a tool with a blade made
out of an insulator, you will be less likely to accidentally short things
out as well
Note that low level signals from the optical pickup like the data (RF) and
other photodiode outputs are extremely sensitive to interference picked up
from a finger on or near the flex cable, a disconnected ground strap, or
possibly even a nearby broadcast antenna. Thus, when the optical deck isn't
fully mounted and connected, there may be unusual behavior - this is probably
normal. Just be aware of this and don't panic, and adjustments should be
made with the unit as close to fully assembled as possible.
You should not need any CD specific tools except in the unlikely event you
get into optical alignment in which case the service manual will detail what
tools and special rigs are needed.
A low power fine tip soldering iron and fine rosin core solder will be
needed if you should need to disconnect any soldered wires (on purpose
or by accident) or replace soldered components.
CAUTION: You can easily turn a simple repair (e.g., bad solder connections)
into an expensive mess if you use inappropriate soldering equipment and/or
lack the soldering skills to go along with it. If in doubt, find someone else
to do the soldering or at least practice, practice, practice, soldering and
desoldering on a junk circuit board first! See the document:
Troubleshooting and Repair of Consumer Electronic
Equipment for additional info on soldering and rework techniques.
For thermal or warmup problems, a can of 'cold spray' or 'circuit chiller'
(they are the same) and a heat gun or blow dryer come in handy to identify
components whose characteristics may be drifting with temperature. Using the
extension tube of the spray can or making a cardboard nozzle for the heat
gun can provide very precise control of which components you are affecting.
Basic cleaning supplies include Q-tips (you may know them as cotton buds),
lint free cloths or paper towels, water, and isopropyl alcohol (preferably 91
percent medicinal grade or better). Note that isopropyl alcohol also goes
by the names isopropanol, 2-propanol, and propan-2-ol. They are all the
same thing.
For info on useful chemicals, adhesives, and lubricants, see
Troubleshooting and Repair of Consumer Electronic
Equipment as well as other documents available at this site.
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مُساهمةموضوع: رد: Disc Players and CDROM Drives    الأحد يوليو 25, 2010 1:15 am

Test equipment



Don't start with the electronic test equipment, start with some analytical
thinking. Many problems associated with consumer electronic equipment
do not require a schematic (though one may be useful). The majority
of problems with CD are mechanical and can be dealt with using nothing
more than a good set of precision hand tools; some alcohol, degreaser,
contact cleaner, light oil and grease; and your powers of observation
(and a little experience). Your built in senses and that stuff between
your ears represents the most important test equipment you have.
A DMM or VOM is necessary for checking of power supply voltages and
testing of sensors, LEDs, switches, and other small components. This does
not need to be expensive but since you will be depending on its readings,
reliability is important. Even a relatively inexpensive DMM from Radio
Shack will be fine for most repair work.
For servo and other electronic problems, an oscilloscope will be useful.
However, it does not need to be fancy. A 10 to 20 MHz dual trace scope
with a set of 10X probes will be more than adequate for all but the most
esoteric troubleshooting of CD players and CDROM drives.
To determine if the laser diode is working properly, a laser power meter is
very useful. Such a device is expensive but is often essential to properly
and safely adjust laser power on many CD players and CDROM drives. However,
for many problems, simply knowing that an IR laser beam is being emitted is
enough. For this, the simple device described in the section:
[ندعوك للتسجيل في المنتدى أو التعريف بنفسك لمعاينة هذا الرابط] is more than adequate.
Alternatively, an inexpensive IR detector card or even some camcorders
can perform the same function.
A stereo amplifier and loudspeakers is essential to allow your most important
piece of audio test equipment to function effectively - your ears. A lot can
be determined by listening to the audio output to distinguish among dirt,
lubrication, servo, control, and other mechanical or electronic problems.
I would caution against the use of headphones as a sudden burst of noise
could blow your eardrums and spoil your entire day.
For testing of optical pickups, some additional equipment will be needed.
However, this will be detailed in the section: Testing of
Optical Pickup Assemblies
.

Test CDs



An inexpensive test CD is nice to have just to be able to play known
frequencies and volume levels. However, it is not essential - any
half decent CD will work just fine for most tests. For many players,
even an old CDROM disc will be adequate to diagnose startup problems.
However, to fully exercise the limits of the player, a disc with a full
74 minutes of music will be needed - Beethoven's Ninth Symphony is a
good choice (even if you are not into classical music) since it is usually
very close (or sometimes slightly over) this length of time.
Keep those old demo CDs or even obsolete CDROM discs - they can be used
for testing purposes. Where an optical deck has a servo problem, the
disc will end up spinning out of control. Stopping this suddenly may
result is the CD scraping itself against the drawer or or base of the
deck and getting scratched. Therefore, some 'garbage' discs are always
handy for testing purposes.
To evaluate tracking and error correction performance, any CD can be turned
into a test CD with multiple width strips of black tape, a felt tip marker,
or even a hand drill! In fact, some professional test discs are made in
exactly this manner.
Also see the sections: "Comments on test discs" and "Custom test CDs using
CD-Rs".

Useful ways to mangle CDs



These suggestions will allow you to put some of those AOL CDs to good use
(well, besides making high tech coasters)!

  • For portable CD players where the designers in their infinite wisdom put
    some of the servo adjustments *under* the spinning disc, a 3-1/2" CD 'single'
    is extremely handy. A normal CD can be cut down as well - to whatever size
    you need as long as enough actual tracks are left so that the directory and a
    few minutes of music/data remain - this could be as little as about 2-1/2" to
    gain access to the adjustments on some models. This surgery is best done on
    a band saw with a narrow fine tooth blade. However, tiny cracks may grow in
    from the edge (overnight, even) if the disc is subjected to any heating or
    stress from cutting or smoothing. Perhaps some annealing is needed to
    prevent these from getting started.
    Note that the lower mass (actually the lower moment of inertia for you
    purists) of the small CDs may alter the servo response somewhat. Putting a
    heavy metal ring or washer on top should help. However, this is still much
    much better than continually having to remove a normal CD to get at the
    adjustments, incrementally moving them one way or another, and then
    replacing the CD to see how you made out. One can grow old doing this! The
    little CDs will enable you to monitor the test points as the adjustments are
    made which is also a definite advantage :-).
    The RCA RP-7903A Portable CD Player is an example of a design where this
    type of modified CD is invaluable for testing.
  • A handy special miniature CD can be made to permit viewing of the focusing
    action on any CD player or CDROM drive as long as you can get to the top of
    the deck while testing. Using a band saw, cut a garbage disc down so as to
    leave only a 1-1/2" diameter center hub with a 1/2" by 1/2" tab sticking out
    from it. This can then be positioned by hand to just cover the lens while
    it is supposed to be doing its focus search.
  • An alternative that will permit you to view both the laser output (from a
    safe distance) and the focusing action is to create a window in a garbage CD
    by removing the label and aluminum layers from an area of the CD at the inner
    tracks - at least a square inch worth. Lacquer thinner (nail polish remover,
    with adequate ventilation) will probably work to remove the label. Fine
    sand paper or steel wool will remove the aluminum and information pits/lands
    (grooves). Then polish with a buffing wheel or old rag.

CAUTION: when using any of these cut-down or windowed test CDs, or 3-1/2"
'singles', avoid staring into the lens when the laser is powered. See the
section: [ندعوك للتسجيل في المنتدى أو التعريف بنفسك لمعاينة هذا الرابط].
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مُساهمةموضوع: رد: Disc Players and CDROM Drives    الأحد يوليو 25, 2010 1:16 am

Getting inside a CD player or CDROM drive



WARNING: you will void the warranty, if any. You may make the problem worse,
possibly much worse. If the player partially worked, it may no longer even
recognize the disc directory. You may accidentally damage parts that were
perfectly fine. If you should decide to then have the unit professionally
serviced, you may find that the shop simply refuses to touch it if they
suspect your tampering. There is nothing worse than having to undo 'fixes'
introduced by a well intentioned do-it-yourselfer where the state of the
player is now a total unknown. At best you will be charged for this effort on
a time and materials basis. It may be very costly. It may not be worth the
expense.
A CD player still under warranty should probably be returned for service for
any covered problems except those with the most obvious and easy solutions.
On the other hand, it is possible that you will do a better job than some
repair shops. You will probably have a better understanding of the basic
theory and will certainly be able to spend much more time on the problem.
And, of course, hobbiest/handyman's time is cheap - as in free.

  • Component CD players. It is generally very easy to remove the top cover on
    most CD players. There are usually some very obvious screws on the sides
    and possibly back as well. These are nearly always Philips head type - use
    the proper screwdriver. Once all the screws are out, the top cover will
    lift up or slide back and then come off easily. If it still does not want
    to budge, recheck for screws you may have missed.
    Once the top cover is removed, the optical deck and electronics board will
    usually be readily accessible.
    In rare cases, removing the bottom cover will provide access to the solder
    side of the electronics board. However, with most CD players, the bottom
    is solid sheet metal and the entire board would need to be unmounted. On
    some, the electronics board is mounted upside-down so there is full access
    to the wiring side once the cover is removed.
  • With most single play designs, the entire optical deck can be lifted out
    after removing 3 or 4 screws. One screw may have a grounding contact under
    it. Replace this in exactly the same position. There may be fragile
    flexible cables. Be careful so as not to damage any. Usually, these cables
    plug in to connectors on the electronics board and permit the entire optical
    deck to be easily replaced if needed (not very common, however, despite what
    you may have heard).
  • For changers, details will depend on the particular model but in general,
    it is more likely that removal of the entire changer mechanism will be more
    involved. However, this is usually not needed unless there is an actual
    mechanical problem with it. With Pioneer cartridge changers, for example,
    the optical deck is easily removed with just 4 screws.
  • For portables, the bottom plate or top cover usually comes off after
    removing several very tiny screws - use the proper size Philips blade
    jeweler's screwdriver and don't lose them. Then, you either have access to
    the bottom of the mainboard or the top of the mainboard blocked mostly by
    the optical deck. With the RCA RP-7903A Portable CD
    Player, it is the latter and the pickup and/or normal size CD
    conveniently block all access to servo adjustments and test points (which
    as is often the case, are ummarked in this RCA unit). These types of CD
    players are usually quite a pain to troubleshoot! Of course, there are
    also many components including most of the large multilegged ICs surface
    mounted on the *bottom* side of the mainboard which makes for even more
    fun should probing be required! You can easily see all the 'stuff' packed
    into a box just slightly larger than a CD!
  • For CDROM drives, both top and bottom covers may be removable depending on
    model. These are more wide open than portables, especially the newer models
    where everything has been shrunk to a tiny optical pickup and circuit board
    with a few large ICs. Unfortunately, adjustments (if any) and test points
    are even less likely to be labeled on CDROM drives. All testing will also
    require a working PC unless your model has built-in audio play capability.

Make notes of screw location and type and immediately store the screws away
in a pill bottle, film canister, or ice cube tray.
When reassembling the equipment make sure to route cables and other wiring
such that they will not get pinched or snagged and possibly broken, or have
their insulation nicked or pierced, and that they will not get caught in
moving parts. Replace any cable ties that were cut or removed during
disassembly and add additional ones of your own if needed. Some electrical
tape may sometimes come in handy to provide insulation insurance as well.
(This applies mostly to portables and CDROM drives - component CD players
are very wide open.
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مُساهمةموضوع: رد: Disc Players and CDROM Drives    الأحد يوليو 25, 2010 1:17 am

CD enhancers



The process of reading a CD is digital. I have seen and heard advertisements
for sonic rings or special magic markers to improve the quality of the digital
audio reproduction. This is total bunk. Don't waste your money. These
products do nothing beyond depleting your pocketbook - and enhancing those
of the vendors.
For more amusement, see the section: Totally worthless
gadgets for CD enthusiasts
.
Along the same lines, some apparently knowledgeable people (knowledgeable in
what you might ask!) have asked if offers of software to turn a CDROM drive
into a CD-R writer should be believed! This is just utter and total nonsense
and what's more likely to happen if you fall for such a SCAM is to become
the new owner of some nasty computer virus! Besides, this must be impossible
since there is no place for a red "write" LED on a CDROM drive! Smile

What about DVD player and DVDROM drive servicing?



DVD players and DVDROM drives have hit the market place in a big way and (if
you believe the hype), DVDs are about to replace CDs totally. Realistically,
this won't happen for some time. In any case, DVD players and DVDROM drives
are *supposed* to accept CDs, CD-Rs, and CD-RWs, so no need to panic just yet.
But availability of new CD based devices will disappear because the cost to
manufacture a DVD player or drive isn't much more than that of a similar CD
unit so manufacturers will want to close down their old production lines and
concentrate on DVDs only.
In any case, eventually all things break, and DVD equipment will be no
exception. Fortunately for us, the similarities between CD and DVD
technology are much more significant than the differences. The inside of
a DVD player looks pretty much the same as the inside of a CD player and,
for the most part, the same problems are likely to occur. Here are some
things to look out for:

  • DVD discs look virtually identical to CDs.
    They are the same size and thickness with the same large center hole and will
    fit perfectly well into a CD player or CDROM drive - but of course won't do
    much there. Despite the tracks and pits being closer together, the
    rainbow/diffraction effects are about the same so a casual glance isn't
    enough to tell them apart but there is always that DVD logo! However, the
    information layer is precisely in the center of a sandwich of polycarbonate
    (each half 0.6 mm thick). (The DVD standard supports a double sided DVD.
    This, of course leaves virtually no room for the label!) More info on
    DVD media, storage capacity, and so forth can be found in the section:
    [ندعوك للتسجيل في المنتدى أو التعريف بنفسك لمعاينة هذا الرابط].
  • The laser in a DVD based device is a very visible red (a wavelength around
    650 nm compared to the nearly invisible IR 780 nm laser used for CDs). This
    is about the same wavelength as used in newer red laser pointers. It is
    still low power (1 mW or less at the objective lens) but the laser will
    appear very bright when it is powered and working correctly. As far as
    hazards to vision, the same recommendations apply - don't look into the beam
    directly but viewing from an oblique angle at 12 inches or more from the
    objective lens should be safe. The eye's aversion reflex will prevent
    damage in any case - you will blink or turn away from a the bright light.
    CAUTION: Some (probably older) DVD equipment may also have a standard CD
    pickup to be able to read CDs. For these, obviously, all the IR laser
    precautions apply.
  • It should be easier to determine if the laser is bad by brightness alone
    though a laser power meter and the manufacturer specifications will still
    be needed in marginal cases.
  • As a result of the march of technology, the optical pickup is likely
    to of simpler design than that in older CD based devices with even fewer
    or no adjustments possible. However, there could be additional complexity
    due to the need to handle DVDs and CDs in the same equipment.
    The use of combined laser diodes and photodetector arrays is likely to
    be quite common if not pervasive. However, pickups may also use
    separate laser diodes and photodiode arrays possibly sharing some of the
    optics or at least part of the beam path in the optical block. In some
    pickups, objective lenses for the CD and DVD lasers can be rotated into
    position as required by applying enough current of the appropriate
    polarity to the fine tracking coils..
  • The same basic functions need to be performed by the front-end electronics
    including amplification of the photodetector array output, and focus,
    tracking, and spindle servos. Much this is likely to be done inside large
    chips with no service adjustments.
  • More functions will be incorporated into fewer surface mount chips.
    Fortunately, failures of the large scale integrated circuits themselves are
    not nearly as common as simple mechanical problems. Better hope so in any
    case as troubleshooting of things like an MPEG decoder is way beyond what
    could be done without a complete service manual, sophisticated test
    equipment, and probably a whole lot more!
  • More plastic and less metal is likely to be used - lighter, flimsier,
    less likely to be serviceable at all.

So, the bad news is that if something breaks inside a large chip, accept
defeat and send the unit in for service. The good news is that most
problems will still be mechanical - dirt, dust, gummed up grease,
bad motors, abuse. From our experience with CD repair, we should be well
equipped to deal with these!
Hopefully, manufacturers have learned from their experience with CDs to make
a more reliable robust product but that may be wishful thinking where the
bottom line is involved. It's still too early to tell.
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مُساهمةموضوع: رد: Disc Players and CDROM Drives    الأحد يوليو 25, 2010 1:18 am

Back to [ندعوك للتسجيل في المنتدى أو التعريف بنفسك لمعاينة هذا الرابط].
CD Player and CDROM Drive Fundamentals


Parts of a CD player or CDROM drive



While CD players and CDROM drives started out and still have much in common,
they are diverging. The optical pickups remain similar but the data processing
and servo systems needed to support 16X speed CDROM technology are much more
sophisticated than those needed for 1X speed CD audio. Therefore, should
you peek inside your shiny new CDROM drive, you may see parts that differ
considerably from those in a old Discman.

Power supply



In component stereos units, there are normally linear supplies and thus very
reliable but easy to repair as well. In portables, they are likely to be
switching supplies, possibly sealed in a shielded can (or at least all surface
mount components), and difficult to troubleshoot and repair.
Usually, at least three voltages are needed: logic power (e.g. +5 Vcc) and a
pair of voltages for the analog circuitry (e.g., +/- 15V). However, some
designs use a variety of voltages for various portions of the analog (mainly)
circuitry.

Electronics board



This contains the microcomputer controller, servos, readback electronics,
audio D/A(s) and filters. Most servo adjustment pots will be located
here. In many cases they are clearly marked but not always. DO NOT
turn anything unless you are sure of what you are doing - and then only
after marking their original positions precisely.

The optical deck



This subsystem includes all of the components to load and spin the disc,
the optical pickup, and its positioning mechanism. Refer to the section:
[ندعوك للتسجيل في المنتدى أو التعريف بنفسك لمعاينة هذا الرابط] for photos of some common
models.

  • Loading drawer - Most portable and many lower cost CD players or CDROM
    drives lack this convenience. Most are motor driven. However, some
    must be pushed in or pulled out by hand.
    Common problems: loose or oily belt causing drawer to not open or close,
    or to not complete its close cycle. There can be mechanical damage
    such as worn/fractured gears or broken parts. The drawer switch may be dirty
    causing the drawer to decide on its own to close. The motor may be
    shorted, have shorted or open windings, or have a dry or worn bearing.
  • Spindle, spindle table, or spindle platter, (we will use these names more
    or less interchangeably) - When the disc is loaded, it rests on this platform
    which is machined to automatically center it and minimize runout and wobble.
    Common problems: Dirt on table surface, bent spindle, dry or worn bearings
    if spindle not part of motor but is belt driven, loose spindle.
  • Spindle motor - The motor that spins the disc. Most often the spindle
    platform is a press fit onto the spindle motor. Two types are common:
    The first is a miniature DC motor (using brushes) very similar to the
    common motors in toys and other battery operated devices. The second type
    is a brushless DC motor using Hall effect devices for commutation. If
    there are more than 2 wires attached to the motor or if it uses exposed
    coils and control board, it is likely of the brushless type. In very
    rare cases, a belt is used to couple the motor to the spindle but most
    are direct drive - the spindle is the motor shaft.
    Common problems: partially shorted motor, shorted or open winding, dry/worn
    bearings, defective electronics. The brushless type are much less likely
    to have electrical problems.
  • Clamper - Usually a magnet on the opposite side of the disc from the
    spindle motor which prevents slippage between the disc and the spindle
    platform. The clamper is lifted off of the disc when the lid or drawer
    is opened. Alternatively, the spindle may be lowered to free the disc.
    Common problems: doesn't engage fully permitting disc to slip on spindle
    due to mechanical problem in drawer closing mechanism.
  • Sled - The mechanism on which the optical pickup is mounted. The sled
    provides the means by which the optical pickup can be moved across the
    disc during normal play or to locate a specific track or piece of data.
    The sled is supported on guide rails and is moved by either a worm or ball
    gear, a rack and pinion gear, linear motor, or rotary positioner similar
    to what is in a modern hard disk drive - in increasing order of performance.
    Note that a single-beam optical pickup can be used with either a linear or
    rotary mechanism. However, a three-beam pickup will not work with a rotary
    positioner because the angle of the pickup changes with radial position.
    Functionally, neither type is fundamentally superior but most manufacturers
    seem to use the three-beam type. Philips/Magnavox (and their other brand
    names) appear to be the principal exceptions.
    Common problems: dirt, gummed up or lack of lubrication, damaged gears.
  • Pickup/sled motor - The entire pickup moves on the sled during normal play
    or for rapid access to musical selections or CDROM data. The motor is
    either a conventional miniature permanent magnet DC motor with belt or gear
    with worm, ball, or rack and pinion mechanism, or a direct drive linear
    motor or rotary positioner with no gears or belts.
    Common problems: partially shorted motor, shorted or open winding, dry or
    worn bearings.
  • Optical pickup - This unit is the 'stylus' that reads the optical
    information encoded on the disc. It includes the laser diode, associated
    optics, focus and tracking actuators, and photodiode array. The optical
    pickup is mounted on the sled and connects to the servo and readback
    electronics using flexible printed wiring cables.
    Common problems: hairline cracks in conductors of flexible cable causing
    intermittent behavior.
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مُساهمةموضوع: رد: Disc Players and CDROM Drives    الأحد يوليو 25, 2010 1:19 am

Typical optical decks



Some examples of common optical decks are shown in the following sets of
photos. Note: The disc loading components and clampers are not shown.
Note: The resolution of the optical deck photos is 37.5 dpi unless otherwise
noted. All other photos include a scale indicator.
The first 4 are from consumer grade CD players:

  • The Pioneer CD Player Optical Deck shows a typical
    sled-type using a PM motor driven screw. This uses a three beam pickup.
    This model (or one similar to it) can be found in both Pioneer single (e.g.,
    PD5100) and changer (e.g., PDM500) type CD players. In the latter case, the
    assembly is mounted upside-down with the clamper on the bottom.
  • The Sony D-2 CD Player Optical Deck shows another
    common sled-type with a gear driven rack. This model (and as far as I know,
    all others from Sony) use three-beam pickups.
    This deck (or one similar to it) can be found in the Sony Model D2 and
    other portable CD players. (The flex cable, a common failure item, has been
    removed to provide unobstructed views.)
    It uses the Sony KSS220A optical pickup which is virtually identical to the
    Sony KSS361A Optical Pickup.
  • The Sony D-14 CD Player Optical Deck is also uses a
    gear driven rack. It has a three-beam pickup.
    This deck is from a very old D-14 portable CD player, possibly only the
    second portable model manufactured by Sony.
    The Sony KSS110C Optical Pickup it uses is
    distinctly different than other more modern Sony models. In addition to
    being larger, the optics include a beam splitter prism, a negative lens in
    the return path, and the objective lens is mounted on a shaft enabling it to
    slide up and down (for focus), and rotate (for tracking).
  • The Philips CD Player Optical Deck provides an
    example of a unit using a rotary type voice coil tracking actuator and uses
    a single-beam pickup.
    This one came from a front loading (flip down see-through door) Magnavox
    Model AH197M37 Modular Stereo System (includes dual cassette, AM/FM radio,
    and turntable).
    CD players and some CDROM drives manufactured by Philips (this includes the
    Magnavox and Sylvania brand names) seem to be the only ones still using
    rotary actuator technology in consumer products. In older versions, parts
    of the optical pickup (like the laser diode) were pluggable and easily
    replaced.

The three below are from CDROM drives:

  • The Sony CDU-31/33A CDROM Optical Deck is typical
    of the mechanism found in lower performance models that use a screw drive
    for sled positioning. The pickup used is a three-beam KSS360A which is very
    nearly identical to the Sony KSS361A Optical
    Pickup (only the shape of the mounting bracket differs). Like its
    consumer CD player counterpart, everything is glued in place at the time of
    manufacture - there are no adjustments.
    The CDU-31A 1X, CDU-33A 2X, and other CDROM drives using this deck were
    probably the most popular models in the early 1990s. The CDU-31/33A used
    the Sony proprietary interface (also available on some sound cards) and were
    certainly nothing to write home about in the speed department. These drives
    used a high quality brushless DC motor for the spindle while other similar
    performance CDROM drives of the era had cheap permanent magnet DC motors
    that were prone to failure. However, they were the only popular front
    loading CDROM drives to NOT have the convenience of a motorized drawer
    mechanism - just a solenoid release. Of course, there was less to break
    down!
  • The Sony CDU-8001 CDROM Optical Deck provides an
    example of a unit using a direct drive linear motor for the coarse tracking
    actuator. The pickup is a three-beam Sony KSS180A - quite similar to the
    Sony KSS361A Optical Pickup but appears to be more
    solidly constructed with at least one additional optical element that may be
    a collimating lens. Unlike most consumer grade pickups, the KSS180A is not
    totally glued together and some adjustment of optical alignment is possible.
    This deck came from a Sony CDU-8001 CDROM Drive Unit - a speedy 1X drive
    (aren't you impressed?) used with a SCSI interface for an Apple MacIntosh
    computer. The NEC Model CDR-82 CDROM Reader and others of the same vintage
    also use the same Sony KSS180A pickup.
    These were of the cartridge loading type (loading mechanism removed). The
    spindle motor is a high quality DC brushless type.
    Some component CD players by Technics (Matsushita) and others (in addition
    to Sony) also used linear motor technology as early as 1983 (possibly even
    before) to provide fast (under 1/2 second) music seek times which is better
    performance than some of the early CDROM drives using screw or gear type
    actuators.
  • The Philips CR-206 CDROM Optical Deck views provide
    an example of a drive using a rotary actuator for both coarse and fine
    tracking. This uses a single-beam pickup where the laser diode and
    photodiode are apparently combined into one package which is mounted in a
    very simple compact optical assembly.
    This deck came from an inexpensive Philips CR-206 2X CDROM drive (vintage
    1994). Note how much smaller this assembly is compared to the Philips CD
    player optical deck, above, which dates from around 1990.

Interestingly, most common popular higher performance CDROM drives (e.g.,
4X, 12X, even 16X or more) do not use linear motors or rotary positioners
to achieve rapid seek times. They use a screw or gear drive powered by a
cheap permanent magnet DC motor! However, they do all use high quality
brushless DC motors for the spindle since these high-X drives put a lot of
stress on this component (especially those which are the true CLV type and
vary speed based on track location). Although the optical pickups themselves
have been simplified and have reduced mass, and the drive mechanism had been
speeded up compared to the typical cheap portable CD player, this type of
implementation is still far from optimal. Therefore, while the transfer rate
may be pretty good (see the section: CDROM drive speed -
where will it end?
for why this really isn't assured even with a 32X
unit), seek times may be mediocre - 250 ms full stroke being typical.
The next two are nearly complete CDROM drives of this type:

  • The Philips PCA80SC CDROM Drive Optical Deck is a
    relatively modern design typical of low cost high spin-rate units. This one
    is an 8X model. The Optical Pickup from Philips PCA80SC
    CDROM appears to be a three-beam type.
    Apparently, many manufacturers used this basic mechanism. I have an Aztech
    CDA-268-01A CDROM drive (2X) which has the same pickup and a very similar
    optical deck.
  • The Teac CD-532S CDROM Drive is another popular
    design used in late model (1998) low cost high spin-rate units. This one is
    a 32X (Max) model with a SCSI interface. The 32X (Max) rating really means
    that it spins at constant speed roughly equivalent to a 13X rate and the 32X
    spec is only achieved for data located near the outer edge of the disc.
    The Sony KSS575B three-beam pickup used in this drive is quite compact but
    of the more complex design using a separate laser diode and photodiode array
    with beam splitter. The optical path is equivalent to that of that of the
    Sony KSS361A Optical Pickup. (See the section:
    [ندعوك للتسجيل في المنتدى أو التعريف بنفسك لمعاينة هذا الرابط].) The guts are
    located in a central box-like object about 1.5 cm on a side. However, the
    pickup is mostly made of plastic - gone are the days of the cast metal
    optical block! While this does make it weigh less, the difference would
    hardly seem to be significant for access speed given the primitive screw
    drive.
    The Sanyo K38N Optical Pickup used in the earlier
    (like all of 3 months!) Teac model, the 16X CD516s, is substantially similar
    to this but of more solid construction. Teac CDROM drives from 6X (and
    possibly below) through this 32X unit appear virtually identical
    mechanically.
    Also notice how little electronics there is in this unit - nearly all the
    circuitry is on the single small circuit board on the left side of the
    bottom view. On all the other CDROM drives, the logic board occupied all
    the space (and more in some models) above or below the optical deck!

Finally, here are photos of DVDROM drives:

  • The Toshiba SD-M1212 DVDROM Drive is typical of
    the DVDROM drives shipped with bundled PCs (I believe this was from a Dell
    Dimension 450 MHz Pentium II system). The most notable feature of the
    optical deck used here is that it really is so similar in appearance to
    those used with late model CD players or CDROM drives. In fact, without the
    DVD logo or other distinguishing markings, it could just as well have been a
    CDROM drive. (Of course, we know that what's inside is quite different at
    least in the details.) I wasn't willing to go any deeper since this is
    still a working unit so there could be internal differences. An update will
    be forthcoming when I get my hands on a broken one!
    Note that it appears to have only a single objective lens. This would
    tend to imply that compromises have been made, most likely for CDs, and
    that performance with them may not be as good as with a dedicated CDROM
    drive.
    One thing that is obvious is the amount of circuitry compared to
    say, the Teac CD532s, above, whose PCB occupied less than 1/3rd of the
    available area. I don't know how much this is due to just being newer
    technology which hasn't been as highly integrated yet as opposed to the
    additional complexity required for DVD decoding and support for CD audio
    and data formats as well.
  • The Optical Path of CD/DVDROM from Sony F390
    Laptop shows the optics and laser diode assemblies from below. The
    objective lens would be where the turning mirror faces. This unit has
    separate DVD and CD lasers, each of the "hologram laser" type with a
    Holographic Optical Element (HOE) for generating the side beams and
    replacing the polarizing beam splitter and other components. One of
    the laser diodes is a Sharp HPD 24T3 according to the markings.
    The DVD laser diode assembly has a 3 way beam splitter crystal on the
    front, 'T' shaped, and the other has a two way splitter '-' on the crystal
    face. DVD Laser Holographic Optical Element shows
    the HOE on the DVD laser diode assembly. Thanks to John LeBourgeois
    (john@121email.com) for these photos.
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مُساهمةموضوع: رد: Disc Players and CDROM Drives    الأحد يوليو 25, 2010 1:20 am

Components of the optical pickup



All the parts described below are in the optical pickup. As noted, the
optical pickup is usually a self contained and replaceable subassembly.
The actual complement and arrangement of parts depends on the specific
pickup design - a number of popular variations on the basic arrangement
are used. Thus, should you actually end up dismantling a dead optical
pickup, it will probably not match this description exactly. While the
relatively old Sony KSS110C Optical Pickup has
most of the same components as described below, the very common newer Sony
and Sanyo optical pickups combine multiple functions into fewer elements.
Typical examples are found in the Sony KSS361A Optical
Pickup and Sanyo K38N Optical Pickup. The
even simpler CMKS-81X Optical Pickup
and Optical Pickup from
Philips PCA80SC CDROM combine the laser diode and photodiode array into
single package and eliminate all of the other optical components except for
the diffraction grating and turning mirror (and the latter could be eliminated
where space permits below the deck). The resulting designs are much cheaper
to manufacture, more robust and reliable, and should have better performance
as well since there are fewer intermediate optical components to degrade the
beam.
Also see the section: CD optical pickup operating
principles
.
Despite its being a precision optomechanical device, optical pickups
are remarkably robust in terms of susceptibility to mechanical damage.

  • Laser Diode - This is Infra Red (IR) emitting usually at 780 nm - near IR,
    just outside the visible range of 400-700 nm. The power output is no more
    than a few milliwatts though this gets reduced to 0.25-1.2 mW at the output
    of the objective lens. A photodiode inside the laser diode case monitors
    optical power directly and is used in a feedback loop to maintain laser
    output at a constant and extremely stable value.
    The photos below show some of the types of laser diodes you may encounter in
    CD players, CDROM drives, laser printers, and bar code scanners:

    • A Variety of Small Laser Diodes (CD, laser printer,
      bar code scanner).
    • Closeup of Typical Laser Diode (from a laser
      printer).
    • Closeup of Laser Diode from the
      Sony KSS361A Optical Pickup (seen 'actual size' in
      the upper left corner of the group photo, above.)

    On an increasing number of pickups, the laser diode and photodiode array are
    combined into a single package. These are recognizable by their 8 or 10
    lead package. See the section: Optical pickup
    complexity
    .
    Common problems: bad laser diode or sensing photodiode resulting in
    reduction or loss of laser output.

  • Photodiode array - This is the sensor which is used to read back data and
    control beams. These are usually integrated into a single chip with a clear
    plastic cover. On an increasing number of pickups, the laser diode and
    photodiode array are combined into a single package. These are recognizable
    by their 8 or 10 lead package. See the section: Optical
    pickup complexity
    .
    The photodiode array for a three-beam pickup has 6 segments - 4 in the
    center (A,B,C,D) and 1 on either side (E,F). Only the center segments
    are used in a single-beam pickup.
    However, there are some CD players and CDROM drives are fitted with complete
    three-beam pickups, but don't take advantage of the side beams - the E and F
    segments of the photodiode array are simply grounded! So, the blurb for
    these models may say "Featuring three-beam pickup" when only a single-beam
    is used! Isn't marketing wonderful? :-).
    Common problems: bad photodiode(s) resulting in improper or absence of focus
    and weak or missing RF signal. A missing bias voltage to the photodiode
    array would also result in lack of output.
  • Collimating lens - This converts the wedge shaped beam of the laser diode
    into nearly parallel rays. Not present in many (newer) designs.
  • Diffraction grating - In a 'three-beam pickup', this generates two
    additional lower power (first order) beams, one on each side of the main
    beam which are used for tracking feedback. It is absent in a 'single-beam
    pickup'.
  • Cylindrical lens - In conjunction with the collimating lens, this provides
    the mechanism for accurate dynamic focusing by changing the shape of the
    return beam based on focal distance. Modern pickups may actually use a
    thick beam splitter mirror or astigmatic objective lense to implement this
    function and/or take advantage of the natural astigmatism of the laser
    diode itself. The thick mirror approach is used in most common Sony KSS
    pickups, for example.
  • Beam splitter - Passes the laser output to the objective lens and disc and
    directs the return beam to the photodiode array. There will be no beam
    splitter (and related optics) if the laser diode and photodiode are combined
    in a single package. Where this is a thick mirror, it also introduces the
    needed astigmatism for focusing (most Sony KSS pickups, for example).
  • Turning mirror - Redirects the optical beams from the horizontal of the
    optical system to vertical to strike the disc. Where space permits under
    the pickup, there is no need for a turning mirror as everything can be
    vertically oriented.
    Common problems: dirty mirror. Unfortunately, this may be difficult to
    access for cleaning. Note: the turning mirror is probably not silvered but
    is coated to reflect IR so do not be surprised if you can see through it.

The previous five items are the major components of the fixed optics.
Outside of damage caused by a serious fall, there is little to go bad.
Better hope so in any case - it is usually very difficult to access the
fixed optics components and there is no easy way to realign them anyhow.
Fortunately, except for the turning mirror, it is unlikely that they
would ever need cleaning. Usually, even the turning mirror is fairly
well protected and remains clean.
Depending on the design of the pickup, many of the components of the optical
system listed above may be missing or combined into a single unit. In fact,
the most modern pickup designs combine the laser diode and photodiode into a
single package with 8 to 10 leads. With this approach, there is no need for a
beam splitter or related optical components as the outgoing and return beams
take nearly the same path. The overall manufacturing process is simplified,
performance is improved, the cost is reduced, and reliability and robustness
are enhanced. See the section: Optical pickup
complexity
.
The following items are associated with focusing the laser beam down to a
microscopic point and maintaining it precisely on the CD's tracks:

  • Objective lens - High quality focusing lens, very similar to a good
    microscope objective with a numerical aperture (N.A.) of 0.45 and focal
    length of 4 mm. (Should you care, the N.A. is defined as the sine of
    the angle from the optical axis to the edge of the objective, as seen
    by the object. An N.A. of 0.45 implies a very fast high quality lens.)
    If you examine CD player objective lenses closely, you will also note that
    they are aspheric - the surface is not shaped like the surface of a sphere
    (as is the case with most of the small lenses you are likely to encounter)
    but its radius of curvature changes from center to edge (it is somewhat
    pointed). Because the light source (laser diode) is coherent and
    monochromatic, a low cost single element plastic molded lens with an
    antireflection coating (the blue tinge in the central area) can produce a
    diffraction limited spot (less than 2 um in diameter) at the disc
    information (pits) layer. An expensive multielement lens system would be
    required if the light source were not coherent and monochromatic. Of
    course, the entire technology would not be practical in this case!
    There is usually a ridge around its periphery to prevent the polished
    surface from being scratched should the assembly accidentally contact the
    spinning disc.
    Note: Some objective lenses (e.g., Philips/Magnavox) have a perfectly flat
    front surface. This would appear to be more susceptible to damage but
    perhaps a mechanical stop prevents contact even at the extreme upper limit.
    The lens is suspended to permit movement in two directions: up and down
    (focus) and toward and away from the spindle (tracking).

    Common problems: dirty lens, dirt in lens mechanism, scratched lens, damage
    from improper cleaning or excessive mechanical shock.
  • Focus actuator - Since focus must be accurate to 1 micron - 1 um, a focus
    servo is used. The actuator is actually a coil of wire in a permanent
    magnetic field like the voice coil in a loudspeaker. The focus actuator
    can move the objective lens up and down - closer or farther from the disc
    based on focus information taken from the photodiode array.
    Common problems: broken coil, damaged suspension (caused by mechanical
    shock or improper cleaning techniques).
  • Tracking actuator - Like focus, tracking must be accurate to 1 um or
    better. A similar voice coil actuator moves the objective lens from
    side-to-side (relative to the tracks - toward or away from the spindle)
    based on tracking feedback information taken from the photodiode array.
    Note: On pickups with rotary positioners, there may be no separate tracking
    coil as its function is subsumed by the positioner servo. The frequency
    response of the overall tracking servo system is high enough that the
    separate fine tracking actuator is not needed. These are also always of the
    single-beam type since the angle of the pickup changes with radial position
    and three-beam tracking control cannot be used.
    Common problems: broken coil, damaged suspension (caused by mechanical
    shock or improper cleaning techniques).
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عدد المساهمات : 34
تاريخ التسجيل : 16/06/2010

مُساهمةموضوع: رد: Disc Players and CDROM Drives    الأحد يوليو 25, 2010 1:21 am

Classification of CD player problems



While there are a semi-infinite number of distinct things that can
go wrong with a CD player, any set of symptoms can be classified as
a hard failure or a soft failure:

  1. Hard failure - door opening/closing problems, disc is not recognized,
    no sound, unit totally dead.
  2. Soft failure - skips, continuous or repetitive audio noise, search or
    track seek problems, random behavior.

Both of these types of problems are common with CD players and CDROM
drives. The causes in both cases are often very simple, easy to locate,
and quick and inexpensive to repair.

Most common CD player problems



While it is tempting to blame the most expensive component in a CD player
or CDROM drive - the laser - for every problem, this is usually uncalled for.
Here is a short list of common causes for a variety of tracking and audio
or data readout symtoms:

  • Dirty optics - lens, prism, or turning mirror.
  • Drawer loading belts - worn, oily, flabby, or tired.
  • Sticky mechanism - dirt, dried up/lack of lubrication, dog hair, sand, etc.
  • Broken (plastic) parts - gear teeth, brackets, or mountings.
  • Need for electronic servo adjustments - focus, tracking, or PLL.
  • Intermittent limit or interlock switches - worn or dirty.
  • Bad connections - solder joints, connectors, or cracked flex cable traces.
  • Motors - electrical (shorted, dead spot) or mechanical (dry/worn bearings).
  • Laser - dead or weak laser diode or laser drive (power) problems.
  • Photodiode array - bad, weak, or shorted segments or no power.
  • Bad/heat sensistive electronic components.
  • Bad or missing optical pickup shield ground.

The following two areas cover the most common types of problems
you are likely to encounter. For any situation where operation is
intermittent or audio output is noisy, skips, or gets stuck, or if
some discs play and others have noise or are not even recognized
consistently, consider these FIRST:

  • Dirty lens - especially if your house is particularly dusty, the
    player is located in a greasy location like a kitchen, or there
    are heavy smokers around. Cleaning the lens is relatively easy
    and may have a dramatic effect on player performance.
  • Mechanical problems - dirt, dried up lubrication, damaged parts.
    These may cause erratic problems or total failure. The first part
    of a CD may play but then get stuck at about the time location.
    If your CD player has a 'transport lock' screw, check that it is in
    the 'operate' position before breaking out the heavy test equipment!
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عدد المساهمات : 34
تاريخ التسجيل : 16/06/2010

مُساهمةموضوع: رد: Disc Players and CDROM Drives    الأحد يوليو 25, 2010 1:22 am

Back to [ندعوك للتسجيل في المنتدى أو التعريف بنفسك لمعاينة هذا الرابط].
Troubleshooting Guide


Instant troubleshooting chart - most common problems and likely causes



The following chart lists a variety of common problems and nearly all possible
causes. Diagnostic procedures will then be needed to determine which actually
apply. The 'possible causes' are listed in *approximate* order of likelihood.
Most of these problems are covered in more detail elsewhere in this document.
While this chart lists many problems, it is does not cover everything that can
go wrong. However, it can be a starting point for guiding your thinking in
the proper direction. Even if not listed here, your particular problem may
still be dealt with elsewhere in this document.


  • Problem: CD player is totally dead.
    Possible causes:

    1. Power outlet, wall adapter, or batteries are dead (as appropriate).
    2. Damage to line or wall adapter cord or plug.
    3. Bad connections or faulty component in power supply (including blown
      fuse).
    4. Defective microcontroller.


  • Problem: CD player is operational but there is no display or partial
    display.
    Possible causes:

    1. Burned out back-light bulb(s).
    2. Bad connections to display panel (totally dead or erratic).
    3. Bad solder connections on display panel (some segment work).
    4. Bad power supply (EL panel filament, driver voltages).


  • Problem: CD player ignores you.
    Possible causes:

    1. Bad connections to one or more buttons or sets of buttons.
    2. Microcontroller failed to reset properly.
    3. Missing/bad voltages from power supply.
    4. Defective microcontroller or other logic.


  • Problem: Drawer does not open or close.
    Possible causes:

    1. Worn, stretched, oily, flabby, belt.
    2. Dirty mechanism or gummed up lubrication.
    3. Stripped gear or other mechanical damage.
    4. Defective motor or bad connections to motor.
    5. Bad drawer/eject button.
    6. Missing/bad voltages from power supply.
    7. Defective microcontroller or other logic.
    8. Dealer antitheft lock enabled.


  • Problem: Drawer operation is erratic.
    Possible causes:

    1. Dirty sense switch contracts or bad connections.
    2. Worn, stretched, oily, flabby, belt.
    3. Dirty mechanism or gummed up lubrication.
    4. Defective motor or bad connections to motor.
    5. Stripped gear or other mechanical damage.
    6. Missing/bad voltages from power supply.
    7. Defective microcontroller or other logic.


  • Problem: Drawer does not close (or open) completely.
    Possible causes:

    1. Worn, stretched, oily, flabby, belt.
    2. Dirty mechanism or gummed up lubrication.
    3. Foreign object like toy, rock, or runaway disc blocking drawer.
    4. Stripped gear or other mechanical damage.
    5. Gear timing is messed up.


  • Problem: CD changer jams when selecting or ejecting CDs.
    Possible causes:

    1. Bad belts, dirt or need for lubrication.
    2. Foreign objects, chipped or broken gears, or other mechanical damage.
    3. Messed up gear timing.
    4. Defective sensor (microswitch or opto-interrupter.
    5. Defective motor, driver, or power supply.
    6. Logic or microcontroller problem.


  • Problem: CD player or CDROM drive damages CDs.
    Possible causes:

    1. Broken, bent, or missing part.
    2. Messed up gear timing (mainly cartridge changers).
    3. Other mechanical fault.
    4. Lens hitting CD due to electronic fault or need to adjust focus servo.


  • Problem: Spindle table loose or sticks to clamper upon eject.
    Possible causes:

    1. Set screw loosened or glue failed holding spindle to motor shaft.
    2. Parts of spindle table broke.


  • Problem: Intermittent or erratic operation.
    Possible causes:

    1. Dirty, scratched, or defective disc.
    2. Dirty lens.
    3. Extended length discs too long for player.
    4. Loading (mechanical) not completed reliably.
    5. Bad connections including missing/erratic optical deck shield.
    6. Cracks in ribbon cable to optical pickup.
    7. Dirty drawer or limit switches.
    8. Power supply or logic problems.
    9. External interference.
    10. Internal damage (e.g., loose parts) in optical pickup.

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عدد المساهمات : 34
تاريخ التسجيل : 16/06/2010

مُساهمةموضوع: رد: Disc Players and CDROM Drives    الأحد يوليو 25, 2010 1:23 am


  • Problem: CD player or CDROM drive overheats.
    Possible causes:

    1. Excessive ambient temperature - sauna or hot stereo components.
    2. Failing/marginal part in power supply, logic, or optical pickup.


  • Problem: Operation is poor or erratic when cold:
    Possible causes:

    1. Gummed up grease or dirt inhibiting movement until warm.
    2. Condensation on optical components due to temperature change.
    3. Bad connections or dirty contacts affected by temperature.


  • Problem: Disc is not recognized displaying 'disc', 'error', etc.
    Possible causes:

    1. Disc loaded upside-down.
    2. Transportation lock engaged.
    3. Dirty, scratched, or defective disc.
    4. Dirty or damaged objective lens.
    5. Loading (mechanical) not completed reliably.
    6. Damaged lens suspension or damaged lens cover preventing free movement.
    7. Dirt, gummed up lubrication, or damage in sled drive mechanism.
    8. Dirty/defective limit switch or sensor.
    9. Defective spindle motor.
    10. Spindle table height incorrectly set.
    11. Bad component in optical pickup.
    12. Cracks in ribbon cable to optical pickup.
    13. Need to adjust servo (or less likely, optical) alignment.
    14. Faulty power supply, electronics, or control logic.
    15. Bad connections including missing/erratic optical deck shield.
    16. External interference.


  • Problem: Disc spins in wrong direction or overspeeds and is never
    recognized.
    Possible causes:

    1. Disc loaded upside-down.
    2. Dirty, scratched, or defective disc.
    3. Dirty or damaged objective lens.
    4. Tracking or CLV servo out of adjustment or faulty.
    5. Bad component in optical pickup.
    6. Microcontroller or control logic problems.
    7. Bad connections or defective ribbon cable to optical pickup.
    8. Defective spindle motor including worn bearings.


  • Problem: Pickup attempts to reset past inner track.
    Possible causes:

    1. Dirty or defective limit switch, bad connections to it, or its
      electronics.
    2. Broken parts preventing limit switch from being activated.
    3. Tracking servo out of adjustment or faulty.
    4. Microcontroller or logic problems.


  • Problem: Player won't let you go near it and/or use your favorite lamp.
    Possible causes:

    1. Missing optical deck shield, ground strap, or other connection.
    2. Outside interference.


  • Problem: Seek operations take too long or fail to complete.
    Possible causes:

    1. Dirty, scratched, or defective disc.
    2. Transportation lock engaged.
    3. Dirty or damaged objective lens, suspension, obstruction, etc.
    4. Tracking or CLV servo out of adjustment or faulty.
    5. Mechanical problems with sled movement.
    6. Faulty sled motor or drive IC.
    7. Faulty control logic.
    8. Bad flex cable to optical pickup.


  • Problem: Search, seek, or play starts correctly, then loses time or
    position.
    Possible causes:

    1. Dirty, scratched, or defective disc.
    2. Dirty or damaged objective lens, suspension, obstruction, etc.
    3. Tracking or PLL servo out of adjustment or faulty.
    4. Stuck button.
    5. Defective sled motor drive IC.
    6. Faulty control logic.


  • Problem: Short distance skipping.
    Possible causes:

    1. Dirty, scratched, or defective disc.
    2. Dirty or damaged objective lens, suspension, obstruction, etc.
    3. Fine tracking servo out of adjustment or faulty.
    4. Weak laser or other defective part in the optical pickup.


  • Problem: Playback gets stuck (rapid repeat).
    Possible causes:

    1. Dirty, scratched, or defective disc.
    2. Dirty or damaged objective lens, suspension, obstruction, etc.
    3. Dirt, gummed up lubrication, or damage in sled drive mechanism.
    4. Transportation lock engaged.
    5. Need for servo alignment.

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عدد المساهمات : 34
تاريخ التسجيل : 16/06/2010

مُساهمةموضوع: رد: Disc Players and CDROM Drives    الأحد يوليو 25, 2010 1:25 am


  • Problem: Occasional long distance skipping or repeating.
    Possible causes:

    1. Dirty, scratched, or defective disc.
    2. Dirty or damaged objective lens, suspension, obstruction, etc.
    3. Dirt, gummed up lubrication, bad belt, or damage in sled drive mechanism.
    4. Transportation lock engaged.
    5. Need for servo alignment.


  • Problem: Player gets stuck at approximately same time on multiple
    discs.
    Possible causes:

    1. Dirt, gummed up lubrication, or damage in sled drive mechanism.
    2. Sled reaching mechanical stop with extended length (>74 minute) disc.
    3. Transportation lock engaged.
    4. Need for servo alignment.
    5. Defective spindle motor.


  • Problem: Various tracking problems on portions of discs:
    Possible causes:

    1. Dirty, scratched, or defective disc.
    2. Faulty spindle motor.
    3. Misalignment of spindle table and sled track.
    4. Need for CLV adjustment.


  • Problem: Repetitive noise at disc rotation rate.
    Possible causes:

    1. Dirty, scratched, or defective (possibly warped) disc.
    2. Dirty or damaged objective lens, suspension, obstruction, etc.
    3. Loose spindle or foreign material on spindle table.
    4. Disc not firmly clamped.
    5. Bent spindle.
    6. Excessive spindle runout due to worn bearing.
    7. Need for servo alignment.
    8. Weak laser or other component in optical pickup.


  • Problem: Audio muting, noise, or distortion.
    Possible causes:

    1. Dirty contacts on RCA jacks on CD player or amp.
    2. Bad connections to RCA jacks.
    3. Dirty/defective muting relay contacts.
    4. Defective components in the analog circuitry (final filter, muting, amp).
    5. Faulty power supply (for audio circuits if used).
    6. Dirty controls (probably on amp unless problem is with the headphones).


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Disc Players and CDROM Drives
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