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


  8.10) CD player or CDROM drive overheats

A CD player which becomes noisy or a CDROM drive that fails to recognize
discs or reliably read data after a few minutes may have a component that
is heating up and changing value.

First confirm that the ambient temperature is not excessive - CD players may
not like to operate in a sauna.  High power stereo components surrounding
the CD player may elevate its internal temperature enough to cause erratic
operation or total failure.  CDROM drives sandwiched in between high capacity
hard drives (this used to be more of a problem than it is today) may overheat.

Assuming your CD player is in an environment which is cool as a cucumber:

In general, there should not be much change in behavior from the instant
power is applied until the next millenniun.  There is not much in a CD player
or CDROM which runs hot and might change characteristics.  However, components
do sometimes fail in this manner.  Problems of this type need to be
diagnosed in much the same way as one would find overheating components
in a TV or computer monitor.

You will need a can of cold spray ('circuit chiller') and an oscilloscope,
if available.  Even a hair dryer on the no-heat setting will work in a pinch.

You are going to have to try cooling various components to try to determine
which one is bad.  However, on a unit that dies completely and suddenly
after it warms this will not be much fun since you will not have ample
opportunity to detect changes in behavior.  On a CD player that will play
but with tracking problems and/or audio noise, you should be able to monitor
the playback quality by simply listening for improvement when you have
cooled the flakey part.  For a CDROM drive, play an audio disc if possible
since this will provide the feedback you need to locate the bad part without
(hopefully) it constantly shutting down due to data errors or inability to
reliably access the file system.

First, I would recommend running with the covers removed and see if that has
an effect confirming a thermal problem.  Next, use the cold spray on
individual components like the LSI chips - quick burst, wait a few seconds
for something to change.  If you are using the hairdryer, make a funnel out
of paper to direct the air flow.  You will need to be more patient with this

If you have a scope, it would be nice to look at the RF 'eye' pattern during
this time and see if it decreases in amplitude and/or quality over the course
of an hour.  If it does, you may have an overheating problem in the laser diode
or its power supply.

  8.11) Operation is poor or erratic when cold

This is somewhat the opposite of overheating and is usually NOT due to a
failing part - electronic components generally misbehave when hot, not cold.

For a system that is not exposed to the elements (e.g., a portable taken from
sub-zero outdoors and immediately put to use indoors), the most likely cause
is mechanical: Gummed up grease and dirt are stiffer when cold and inhibit
motion of the sled and other moving parts until the unit warms up.

However, for automotive units and portables - which are not well sealed,
condensation can form form on the optics if a cold player is exposed to a
humid environment.  This may be the case when you get into your car on cold
days until the CD player itself warms up to ambient temperature.  If a VCR
or camcorder detects condensation, it will flash a DEW warning and refuse
to do anything to protects itself.  For VCRs, this is critical because you
could end up with a mess and expensive repair bill if the video tape were to
stick to the spinning video head drum.  Unfortunately, CD players don't have
this feature since nothing catastrophic would happen.  A warning would be
nice, however!

A third possibility is that there are bad connections or dirty contacts
in the unit that are affected by temperature resulting in erratic behavior
as they expand.

Chapter 9) Startup Problems

  9.1) What is a startup problem?

Startup problems cover all situations where the player does not successfully
read the disc directory.  Nearly everything in the optical deck and much of
the mainboard electronics needs to be functional to read the directory.
Therefore, a single failure in any of a large number of places can prevent
successful startup (and subsequent play).

* On a single play unit, failure of the startup sequence may result in
  a display of no disc, disc, error; a full calander but no disc info;
  or it may just open the door and challenge you to provide it with a
  proper meal.

* On a changer, failure of the startup sequence will likely result in
  a similar display but then the unit will move on to the next position
  in the carousel or cartridge.  It will likely remember that it was
  unsuccessful at loading a disc for each position and eventually give
  up once all possible discs have been tried.

Possible causes for startup failure include: defective disc, dirty lens,
defective laser or photodiode array, bad focus or tracking actuator or driver,
dirty track, lack of or dried up lubrication, dirty or bad limit switches or
sensors, defective spindle motor, faulty electronics or control logic, damaged
parts, faulty optical alignment or need for servo adjustments, a missing
optical deck shield, or outside interference.

On the one hand this is a large number of possibilities.  The good news is
that with such a large number of possibilities, there is a good chance the
problem will be minor and inexpensive to fix.

Don't overlook the trivial: are you loading the disc correctly?  Most CD
players want the disc label-side up.  However, some, like Pioneer magazine
type changers want the label-side down.  If you have just acquired the
CD player, don't overlook this possibility.

On some poorly designed players - or where you are located in proximity to a
high power (or possibly not so high power) radio station - outside
interference can get into the player via the audio cables or line cord.  A
light dimmer on the same circuit might also produce interference via the power
supply.  Once inside, almost any type of behavior is possible.  See the
section: "Player won't let you go near it and/or use your favorite lamp" for
testing procedures.

  9.2) Startup sequence

There will be variations on the exact startup sequence of events depending
on the type of player and its design.  The result may be a blank display,
display of the word 'disc', 'error', --:--, flashing display, etc.  In any
case, you don't get your music.  By understanding the following summary as it
applies to your player, you should be able to determine what is going wrong.

A dirty lens - perhaps not even visibly dirty to your naked eyeball - can
result in any number of startup (or other) problems.  Therefore, cleaning of
the lens should be done before suspecting more obscure mechanical or
electronic faults.  See the section: "General inspection, cleaning, and lubrication".

BTW, as hard as it may be to believe, there have been rare instances of the
objective lens falling off!  So, if you don't see one, check for it bouncing
around in the bottom of the player!  See the section: "Objective lens popped out".

If this is a new player (at least for you) or has just been moved, check to
see if it has a transportation lock to prevent the pickup from bouncing around
during shipment.  This is common on older units but you may find such a
feature on the latest CD players and CDROM drives where a linear or rotary
positioner is used to achieve high speed access.  The lock migh prevent the
sled from moving to the area of the disc directory (and of course, from
playing properly).

What the CD player should do when a disc is inserted:

1.  Drawer closes (or with portables, lid is closed manually) and CD is
    clamped to spindle.

2.  Interlock (if present, always in portables) engages.  In others, there
    may be an optical sensor or the optical pickup may act as its own disc
    sensor assuming a disc is present when it detects reflected light from the
    disc's reflective information layer.

3.  Pickup resets to starting (index) location toward center of disc usually
    found with limit switch or optical sensor.

4.  For the following, refer to the diagram below or the slightly nicer
    version: CD Player Front-End showing the photodetector organization
    typical in units with a 'three-beam pickup'.  E and F will be absent in
    units with a 'single-beam pickup', though there may be other segments.
    The four quadrant photodetector is present in all systems.

    The front-end circuitry shown is for descriptive purposes only; refer to
    an actual CD player schematic for details.

                      |<--- Photodiode Array ---->|
    ---------_________ +---+  +-| A | B |-+  +---+
    Track--->          | E |- | +---+---+ | -| F | ________
                       +---+  | | C | D | |  +---+         ---------
                         |    | +---+---+ |    |           Track--->
                   /|    |    |   |   |   |    |
     Focus       / +|----|----+---|---+   |    |    
     Error o---<    |    |    |   |   *   |    |    |\
     (A+D)-(B+C) \ -|----|----|---+-------+    +----|+ \       Tracking
                   \|    |    |   *       |         |    >---o Error
               FE Amp    +--------------------------|- /       (E-F)
                              |           |         |/ TE Amp
     * Since the photodiodes  |           |           
       are current sources,   |           |         |\
       the simple junctions   |           +---------|+ \       Data Out
       implement a sum.       |                     |    >---o RF Test Point
                              +---------------------|- /       (A+B+C+D)
     All Amps: current mode inputs.                 |/ DO Amp

    The main return beam is detected by the array, ABCD.  The tracking beams
    return to E and F.  E is offset slightly off track on one side and F on
    the other.  Average signals from E and F will be equal when centered
    on track.

4a. Laser is turned on and focus search routine is started to position lens at
    correct vertical position.  Once correct focus is achieved, focus servo is
    activated to maintain it.  Focus, which must be accurate to 1 um, operates
    as follows: The optical path in the pickup includes a cylindrical lens
    (or this may be an equivalent component or astigmatic objective lens)
    which causes the laser beam spot to be circular when correctly focussed but
    elliptical otherwise with the major axis of the ellipse being offset 90
    degrees depending on whether the lens is to close or too far (e.g.,
    major axis of +45 degrees for too close and -45 degrees for too far).
    Focus Error = (A+D)-(B+C) = 0 for correct focus since with the circular
    spot, the outputs of all four quadrants will be equal.

4b. Disc starts spinning up to 500 rpm and Constant Linear Velocity (CLV) servo
    is activated to maintain correct speed.  CLV servo uses a PLL to lock to
    clock transitions derived from data read off of disc.  Data is derived from
    A+B+C+D.  (A buffered version of this signal can be monitored at the 'RF
    Test Point'.)  A partially shorted spindle motor can result in the disc
    spinning but never quite reaching the required 500 rpm.

4c. Tracking servo is activated to maintain laser beam centered on track.
    With 'three-beam pickup', 2 additional laser spots are projected onto
    the disc in front of and behind main beam.  These are offset on each side
    of the track just enough so that Tracking Error = E-F = 0 when centered.

    With a 'single-beam pickup', similar information is derived using only the
    main beam since Tracking Error = (A+B)-(C+D) = 0 for correct tracking.

5.  Disc directory is read and displayed.

6.  Unit shuts down awaiting command or goes into play mode depending on
    how it was activated.

The steps listed as (4a,b,c) may or may not be performed concurrently.
If any of 1-5 fail, then the laser is turned off and the machine will
display some kind of error no disc message (typically, it may display
Error, Disc, or go blank) and return to idle mode, or in the case of a
changer, load the next disc and try again.

  9.3) Procedure for validating the startup sequence

The following procedure is used when the disc is not recognized but the drawer
closes completely.

First, double check the drawer closing/opening mechanism.  Without exception,
Sony CD players which have belts need them cleaned and eventually replaced.
If the drawer does not close completely, then the disc may not be clamped
properly or other erratic problems may occur.

Once you have verified that this is ok, you need to determine that the lens is
clean.  In general, the lens should look shiny with a blue tinge.  Any scum or
crud can degrade performance.  You may have to remove part of the clamping
mechanism to be able to see the lens.  If it is not perfectly shiny, clean it
using the procedures in the section: "General inspection, cleaning, and lubrication".

Assuming that this does not improve the situation, the next step is to verify
that the pickup has reset itself to the inner (center) track of the disc.  If
necessary manually move the pickup away from the center by turning the
appropriate pulley or gear, or in the case of a linear actuator or rotary
positioner (no gears or belts), just push the pickup gently and observe the
behavior when a disc is loaded.  If you are not able to move the pickup
smoothly from one stop to the other, make sure any shipping lock is
disengaged!  The pickup should move smoothly toward the center, usually
tripping a limit switch and stopping.  If there is no movement or movement is
jerky or the pickup gets stuck at some point, then lubrication may be needed
or the motor or drive circuitry may be faulty.  Also, check for broken or
damaged gear teeth, a slipping belt, and misaligned or damaged tracks.
Measure the voltage on the motor that moves the pickup.  If there is none or
it is very low (under a volt or so), then there is a problem with the motor,
its driver, or the system controller.

Determine if the machine attempts to focus.  On portables, it is sufficient to
defeat the door interlock to get the operations associated with reading of the
disc directory to begin (you may need to press play - this is model
dependent).  In some component CD players, a disc actually has to be present
to block an optical sensor.  You should see the lens moving up and down (at
least one of these directions will have smooth movement) once or twice about 2
mm.  If a disc is in place, then the lens should quickly stop at the
appropriate focus position.  Admittedly, observing the lens may be difficult
or impossible with the disc in place.  Dentists are probably good at this!

If the focus action is identical whether a disc is in place or not - i.e., it
keeps up the search pattern and then gives up - verify that the laser is being
powered.  In most cases, you should be able to see a tiny spot of red
appearing light when the lens is viewed from an oblique angle during the focus
search.  From a safe distance of at least six inches and 45 degrees or more
off to one side, you should be able to see this dim red light in a darkened
room while the unit is attempting to focus.  If you see this, you can assume
that the laser is being powered though it is not a sure test for an actual IR
laser beam or proper optical power output.  In most cases, however, the red
light indicates that the laser is working.  If there is no dot of red light,
then either the laser diode is bad, it is not being powered, or you are not
looking from the correct angle.  An IR detector would confirm at least that
there is an IR emission which in most cases means the laser is working (though
possibly not at the proper power level):

* You can purchase an inexpensive IR detector card from an electronics

* A tester can be constructed using a photodiode, a few resistors, a general
  purpose small signal transistor, and an LED running off a 9 V battery.  See
  the section: IR detector circuit.  This will useful for testing IR remote
  controls and other IR emitters as well.

* If you have a modern camcorder (one with a CCD pickup, not a tube), it may
  be sensitive to IR as well but using one to test a CD laser would be pretty
  clunky to say the least (you would probably need to grow an extra arm or
  two).  However, viewing the beam pattern projected on a white sheet of paper
  will enable the gross alignment to be checked easily - it should be fairly
  symmetric and centered above the lens.

If the lens is hitting the disc at the top of its excursion, there is a
possibility that the spindle table has been pushed too far down - by something
falling on it, for example.  (A bent shaft and wobbly spindle is also a
possibility in this case.)  Such an occurance is much more likely to have
happened to a top loading boombox or protable than a drawer loading machine.
(A friend of mine used to pound on his Sony boombox when it would not cooperate
and this didn't help matters.)  While hitting the disc with the spindle table
set at the correct height is not impossible on some players, it is unlikely.
(On most lenses, a ring around the outside of the lens itself prevents the
critical central area from actually contacting the disc so accidental contact
does not usually damage the lens but may scratch the disc.  However, I have
a portable where even this was not enough - the lens was seriously scratched

Similarly, if the spindle is too high, the lens may not be able to reach
up to the proper focus position.

On a player with the height adjusted properly, there is usually about 2 mm
between the laser shroud and the bottom of the disc.  The spindle height is
not super-critical but if it is way off, proper focus cannot be established.
See the section: "Spindle motor replacement".

Incorrectly adjusted focus offset or gain may result in the lens search
pattern being too high or too low as well.

Once focus is established (and sometimes concurrent with this operation),
the spindle should begin to turn and quickly reach 500 rpm.  The speed
may be ramped up or controlled in some other search pattern since there is
no speed feedback until the data coming off of the disc is available.
A partially shorted motor will prevent the spindle from reaching 500 rpm
even though the disc will spin.  Check the voltage on the spindle motor
when it starts the disc spinning.  It should reach 2 volts or more.  If less
than this but not zero, a partially shorted motor or weak driver is likely.
If zero at all times then there may be a bad driver or the machine may not
realize that focus was established and is not issuing the spindle motor
start command.  The required speed of 500 rpm - just over 8 revolutions per
second - can be estimated by using a disc with a dramatic label or putting
a piece of tape on the side of the disc that is visible and watching it spin.

Note that a dirty lens can sometimes result in symptoms similar to a bad
spindle motor so cleaning the lens should always be the first step when
servicing a CD player.  I almost learned this the hard way.

Once the disc reaches the correct speed, the speed control (Constant Linear
Velocity, CLV) and tracking servos will be activated (or the tracking servo
may actually have been active all along) and directory data will be read
off of the disc.  Either of these could be faulty and/or misadjusted making
it impossible to access the disc directory.

During the time that the disc is spinning and the player is attempting to
read the disc directory, listen for that 'gritty' sound that CD players make
during normal operation. It is a byproduct of the focus and tracking servos
constantly adjusting lens position - the rapid movements of the lens produce
audible sound like a loudspeaker - and its presence is a good indication that
(1) the laser is working and (2) focus is being maintained.

On certain CD players, for example many Pioneer models, there is a TEST mode
which enables many of the individual functions such as focus and tracking
that are normally automatic to be manually enabled.  This is a very
useful aid is diagnosis and in adjusting a machine from an unknown state
as would be the case if someone else twiddled every internal adjustment
they could find!  See the section: "Pioneer PD/M series test mode".

  9.4) Disc spins in wrong direction or overspeeds and is never recognized

The CD should always spin clockwise as viewed from the label side of
the CD.  This is usually the top but for some players you load the CD
upside-down (e.g. Pioneer magazine type changers).  If the CD should
consistently start spinning counterclockwise and continue for more than
a fraction of a revolution, or should the CD ever spin at a much faster
rate than normal - as though it is about to take off, there may be a serious
problem with the optical pickup, spindle servo, or control logic.  However,
behavior of this type could simply be the result of any of a number of minor
faults which you can diagnose and repair including a dirty lens, the disc being
loaded upside-down, or the internal adjustments being messed up due to someone
violating rule #1 - never wildly tweak any internal adjustments!

First confirm that the disc is loaded correctly and that the lens is clean.

Check for bad connections and cracks in any printed flexible cables to the
optical deck as well.  Clean and reseat connectors just to be sure.  Where
a brushless DC type spindle motor (rather than a PM motor) is used, even a
bad connection to the motor could result in strange behavior due to a missing
phase or feedback signal.

If this does not help, attempt to perform a servo system adjustment.  If you
have a service manual, by all means follow it!  If not, see the chapter:
"Servo Systems and CD Player Adjustments".  If it is a Pioneer CD player
or changer, see the section: "Pioneer PD/M series servo adjustment procedure"
(this may also apply to other non-Pioneer models with only minor changes).

  9.5) Pickup attempts to reset past inner track

Sled motor doesn't stop at the inner track but keeps clicking, clunking, or
whirring until the controller gives up and displays an error.

This may be due to a dirty, worn, or gummed up limit switch, bad connections,
bad mechanical alignment or broken parts, or logic problems.

Most limit switches are mechanical and easily checked with a multimeter.
Those that use exposed contacts can be cleaned and burnished; sealed switches
found to be erratic should be replaced though spraying inside though any
openings may help.  I have disassembled and cleaned similar type switches
(they snapped apart) but it is not fun.

Make sure the limit switch actually gets tripped when the sled reaches the
area of the innermost track.

Check for bad connections between the switch and the controller.

Logic problems may be difficult or impossible to locate even with schematics.
However, you might get lucky as was the case with a CDROM drive with a bad
74LS04 in the drawer switch interface!

  9.6) Player won't let you go near it and/or use your favorite lamp

Symptoms may include a player where the audio becomes noisy or even stops
completely or stuttering or skipping occurs, if you touch or go near it!

Note that there is an entire chapter: "Tracking (Seek and Play) Problems".
However, since a possible cause of this sort of behavior is more general
in nature and can affect many different aspects of CD player operation,
these faults are described separately.

* One area that may be overlooked as a cause is the shielding of the pickup low
  level signal cable and any metal parts of the optical deck.  These should all
  be connected to analog ground of the electronics board.  If this is missing or
  broken, there can be all kinds of strange symptoms.  If you have recently
  disassembled the unit and it is now behaving in this manner, this is a very
  alikely - easy to fix - possibility.  Check for a missing ground strap, jumper,
  or clip.  Hint: it has probably fallen under your workbench!

* External interference from a high power (or not so high power) radio station or
  even a light dimmer on the same circuit may make its way into the electronics
  and produce all sorts of strange behavior.

  On some poorly designed players - or where you are located in proximity to a
  high power (or possibly not so high power) radio station - outside interference
  can get into the player via the audio cables or line cord.  A light dimmer on
  the same circuit might also produce interference via the power supply.  Once
  inside, almost any type of behavior is possible.  If your problems seem to
  depend on the time of day, check out this possibility by relocating the CD
  player and seeing if the behavior changes substantially.  Disconnect the audio
  cables and see if it now displays the disc directory and appears to play
  properly - try headphones if possible.

  It may be difficult to eliminate the effects of this interference without
  moving the radio station or not using your favorite lamp.  However, relocating
  the CD player or even just its cables and/or plugging it into a different
  outlet may help.  Fortunately, these sorts of problems are not that common.

Chapter 10) Tracking (Seek and Play) Problems

  10.1) Description of seek and play problems

The term 'seek' refers to the operations needed to move the pickup and locate
the exact position (time) on the disc to begin or continue play (during
programmed track selection).  The term 'play' is self explanatory and refers
to the condition of reading off data continuously while outputting audio
signals to the headphones or amplifier.  Somewhat in between are the actions
performed during audible search forward or backward.

When playing at normal speed (e.g., 1X for music), the fine tracking servo
maintains the laser beam centered on the track (pits of the information
layer) of the CD while the coarse tracking servo moves the entire optical
pickup as needed to keep the tracking error within well defined limits.
See the section: "Servo systems".  Failures or marginal performance of any
of these systems can result in audio noise, skipping, sticking, or failure
of seek and search operations.

The following types of problems are common:

* Seek failure resulting in the inability to locate the starting track.
* Short or long distance skipping backward or forwards or sticking.
* Occasional or repetitive noise, clicking, or muting.

A dirty or badly scratched or warped disc, a dirty lens, damage to the lens
suspension or a smashed lens cover, a defective or improperly set AC adapter
(voltage too high, too low, inadequate current capacity, poor regulation, or
too much ripple), weak batteries or wrong type of batteries (NiCds may not
work in a player designed for normal 1.5 V AAs), or a missing optical deck
shield ground connection can result in similar symptoms as well.

Thus, if you experience any of the problems discussed in the next few sections,
first confirm that the disc is not dirty, scratched, smudged, warped, or
otherwise defective - inspect and clean it if necessary and/or try a different
one.  Check the AC adapter or batteries.  If no problems are found, manually
clean the lens.  If you recently had the player apart, check the grounding
of the optical deck.

The importance of doing these simple things first cannot be overemphasized as
many apparently unrelated problems can be caused by a bad disc, dirty lens,
or bad power.

Then, check for obvious mechanical faults like gummed up lubrication or a
worn spindle bearing.  Only after these efforts do not solve your problem
or at least identify the cause, should you consider adjusting any of the
servo systems.

  10.2) The seek process

Proper readout of the digital audio or data on a CD depends on the proper
functioning of the focus, and tracking servos and the system controller.
The basic operation of these has been confirmed by successful reading of
the disc directory.  However, additional logic and drive electronics are
called into action to actually seek to a particular track (even if it is
the first) and switch to play mode.

When initiating play or seeking to a particular track, the player must go
through the following 4 steps (exact details may vary depending on the design
of your particular CD player):

1. The sled motor moves the pickup to the estimated position of the selected
   track based on its time code.  For long jumps, this may be done partially
   open-loop.  However, at some point - possibly from the start - the time
   code on the CD will be sampled periodically to determine instantaneous
   sled/pickup position.

   To access the time code, tracking must be stable for long enough to read
   1/75th of a second of data (requiring tracking lock for up to 1/37th of
   a second if it just missed the start of a data block).  This is possible
   even when the sled is moving since the fine tracking servo can backtrack
   to maintain tracking lock.

2. Once in the vicinity of the selected track, the sled is moved in small
   increments forward (and backwards if it overshoots) until the lens is
   within the 'acceptance window' of the fine tracking servo.

   Again, the time code is read and a direction and distance is selected
   by comparing it with the desired destination.  On many players, you can
   actually hear this iterative process (by listening to the player - not the
   speakers) when using the >>| or |<< select keys.

3. With the fine tracking servo is engaged, the position of the lens is then
   jogged to home in on the exact time of the start of the track usually
   without moving the sled.  Once it is within, say 25 frames prior to the
   desired starting location (1/3 second), it will just start playing but
   with the sound muted.

   Sometimes, it may be possible to have stopped at just the wrong position
   just out of range of where it wants to be (using the fine tracking servo
   alone) so that the sled would then move based on the normal tracking error
   criteria - exceeding a threshold (since the fine tracking locked).

4. Once the exact starting point is located, audio is unmuted and normal
   play begins.

Though all of these steps require the optical pickup to be operational, they
each depend on different parts of the servo circuits - a failure could result
in one of these steps not operating properly.

Audible search maintains the fine tracking lock but jogs the lens to move
forward or backward.  Audio is unmuted for a fraction of a second and then
this process repeats.  Thus, (3) and (4) are repeated (with the jog direction
determined by which button is pressed) continuously.

Issuing a PAUSE command results in the fine tracking servo jogging the lens
to maintain a constant position (time code).

While playing, searching, seeking, or in pause, focus must be maintained
continuously despite spindle runout, a moderately warped disc, and minor
bumps or vibration.  Thus if focus adjustment is marginal, loss of focus
may complicate your diagnosis of tracking problems - make sure focus is
solid before moving on to tracking or rotation problems.

  10.3) Diagnosis of erratic play

If you have a suitable oscilloscope, the following approach may help to narrow
down and correct the problem.  If not, you can use the alternative techniques
outlined in the sections relevant to your symptoms.  See the section: "The CD player 'eye' pattern" for a description of typical test points and signals.

Start with the RF test point.  It probably should be about 1 V p-p.  (However,
the exact value will depend on model.)  This should be the eye pattern.

Determine if it is weak, noisy, or erratic.  If you can get it somewhat
stable, try tweaking the various offsets (RF, focus, tracking) just a bit
to optimize its appearance.  The waveform should look approximately like
the diagram in the the section: "The CD player 'eye' pattern".

If the eye pattern is erratic, look at the focus error and tracking error
test points.  These should look like high frequency random noise but not be
jumping or changing erratically.  The DC offset of the tracking error should
increase gradually as the lens moves to follow the spiral track and then jump
back once the sled motor kicks in to re-center the pickup.

Use the buttons that move the sled to see if the rotation speed is correct
at the beginning, middle, and end of a disc. (500-350-200 rpm).  If it has
trouble at the beginning, a bad spindle motor or driver is possible; if it
has trouble at the end of the disc, a bad driver is possible.  Adjustment of
the PLL or VCO pot may correct for these types of problems.  Check the eye
pattern at the start and end of a long disc as well. 

  10.4) Seek operations take too long or fail to complete

This means that attempting to seek to a particular music track results in
this never completing or going to the wrong place.  Alternatively, even
pressing the search forward or backward buttons may result in the failure
to go where directed.  The player may abort the disc and stop or (in the
case of a changer) go on to the next one.  Even the first track may never
be played.  However, it is assumed that the disc directory is read reliably.

Common causes: dirty lens, bad disc, tracking or CLV PLL adjustments needed,
transportation lock engaged, mechanical problems with pickup movement, faulty
sled motor or drive IC, faulty control logic, bad flex cable.

* If your CD player has a 'transport lock' screw, check that it is in the
  'operate' position.

* Inspect the disc for badly scratched or smudged areas and other defects or
  try another one.  Clean the lens.

* Eliminate the possibility of mechanical problems - see the section:
  "Testing the sled for mechanical problems".

* Check for a printed flex cable that has hairline cracks in one or more
  traces.  As the pickup moves past a certain location, a critical connection
  may open up resulting in this behavior.  Such a cause is more likely if the
  player aborts without warning during a seek or search.

If none of this uncovers the problem, there may be sled motor driver,
logic, controller, or other electronic problems.

Search, seek, or play starts correctly, then loses time or position.

You may select music track 5, the player goes there quickly, starts to
play but immediately jumps to another location forward or backwards or
resets to the start of the disc.  Or, if play is started at any location,
instead of playing forward as would be expected, the numbers in the display
count down.

Common causes include a defective disc, dirty lens, stuck button, need to adjust
coarse tracking offset or tracking balance, bad sled motor drive IC, or faulty
control logic.

* First, try a different CD to make sure it is not defective.  Or, try different
  locations on the same CD as the CD would likely not be defective over its entire

* A dirty lens is always possible.  Clean it.

* This may be a problem with coarse tracking offset or tracking balance.
  See the section: "Adjustment procedure for noise or skipping"

* To eliminate the possibility of a stuck button, it may be possible to
  operate the player with the relevant part of the front panel control
  unplugged using the remote control (if it has one) or the 'press the
  drawer' method of starting play.  If either of these results in the disc
  playing normally, then a stuck or dirty button is likely.  This will most
  likely require the disassembly and cleaning or replacement of the affected
  push button switch.

* It is possible that the sled motor driver IC or its logic is bad: when
  the tracking servo is closed, its output is highly unbalanced due to an
  internal failure.  Unless you want to take a shot in the dark and replace
  the chip, further troubleshooting of this problem will likely require a
  service manual.  However, I have lucked out when the driver IC on a Pioneer
  CD player was running excessive hot - replacing it cured this problem.

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Written by Samuel M. Goldwasser. | [mailto]. The most recent version is available on the WWW server http://www.repairfaq.org/ [Copyright] [Disclaimer]