Notes on the Troubleshooting and Repair of Compact Disc Players and CDROM Drives


Chapter 6) CD Player and CDROM Drive Fundamentals

  6.1) 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 peak inside your shiny new CDROM drive, you may see parts that differ
considerably from those in a old Discman.

  6.2) 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)

  6.3) 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 merking their original positions precisely.

  6.4) 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:
"Typical optical decks" 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
  provide 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 principle 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.

  6.5) Typical optical decks

Some examples of common optical decks are shown in the following 3 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.  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

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

* 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

* 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

  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

  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: "Sony KSS series optical pickups".)  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!

  6.6) 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

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 .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

* 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 combine
  this function into an astigmatic objective lens and/or take advantage of
  the natural astigmatism of the laser diode itself.

* 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.

* 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 .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 .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).

  6.7) 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.

  6.8) 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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