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


  14.8) Audio whine (not from speakers) and/or muddy sound with Sony CD players

Generally, the only symptom is a CD players that sounds unhappy - there are
no audio or tracking problems.  However, in severe cases, there may also be
audio degradation described as "muddy sound".

(No doubt, a non-Sony approved weight would work equally well for the solution

(From: Lance Edmonds (lanceedmonds@xtra.co.nz)).

The whine problem usually occurs with KSS240A and KSS213A optical pickups, and
is caused by a mechanical resonance. There are at least 2 service bulletins
describing the fault and the cure.

Sony sells a special weight to fit to the pickup, and also a felt pad to add
to the bottom of the top clamp assembly. Both these items cure this problem.
Some machines may only require the weight.  

In rare circumstances the resonance can interfere with the tracking/focus
servos enough to cause skipping.  Usually the problem is not easily repeated,
however certain light weight disc's may trigger the problem repeatably.

Note that the resonance usually only occurs on the first few tracks if at all,
and some disc's will play with the problem never showing up. Seems to be a
disc weight/thickness/density problem.

Contact your official Sony service office for the part numbers etc.

  14.9) Notes on Sony CDU31/33A CDROM drives.

(Refer to the photo of the Sony CDU-31/33A CDROM Optical Deck for parts

Both these drives use similar optomechanical technology.  The CDU31A is
1X (though I have heard that some versions of this may be 2X, unconfirmed)
and CDU33A is 2X.

Many have complained about the lack of a motorized tray.  What this does
provide is a very simple robust mechanical design.  A solenoid latch keeps
the drawer shut.  When the solenoid is activated (or the emergency release
is pressed) the drawer pops out about an inch.  Pulling the rest of the
way is manual.  The movement of the drawer clamps/unclamps the disc to
the spindle with a powerful magnet.  Except from gross abuse, there is little
to go wrong mechanically.

There are only two major components: the Printed Wiring Board where all
the active electronics are located and the Optical Deck including laser,
optics, and pickup worm drive mechanism.

The other parts include the upper plastic casting and metal shroud,
solenoid latch assembly, right and left guide rails, drawer assembly,
and front bezel, two springs, bottom plate, 6 screws.

There are only two electrical connectors inside: one flat printed cable
linking the PWB and optical deck and a two pin connector supplying power
to the eject solenoid.  This is in pleasant contrast to some other CDROM
drives I have seen with a half dozen or more small connectors spread
all over the PWB making removal and testing very difficult and risky.

  14.10) Disassembling the Sony CDU31/33A CDROM drive

The only major cautions are to not lose any of the small screws or springs
and to avoid damaging the multi-conductor flexible cable linking the
electronics to the optical assembly.

The following procedure takes about 5-10 minutes:

0. Place the unit upside-down on a soft surface.

1. Remove 4 philips head screws securing bottom cover.  Set bottom cover aside.

   You will now have access to the electronic adjustments for focus, tracking,
   etc.  If this is what you are after, no further disassembly is needed.

2. Unclip the front bezel.  Slide it out with the tray as far as it will go.
   You may need to manually activate the eject mechanism with a paperclip.

3. Remove 2 philips screws securing Printed Wiring Board (PWB).  Gently lift
   PWB and disconnect connector to latch solenoid assembly in front of unit.

4. Gently lift PWB further and disconnect flexible cable connector on optical
   assembly.  Mark the orientation so there will be no doubt about getting
   it correct if you need to reassemble on the workbench for testing.
   There is a latch at each end which you push away from the connector 1 mm
   or so.  The cable will than come out easily.

   You now have partial access to the optical assembly sled drive.  Cleaning
   and lubrication of these components is now possible.

5. Lift the latch solenoid assembly up, remove and set aside.

6. Using a pair of fine needlenose pliers or tweezers, disconnect and set
   aside the two tray retraction springs.  Note their position and orientation.

7. Remove the two plastic guides - one on each side.  There are little
   tabs that you will need to depress and then lift each guide straight up.

8. The entire deck can now be slid forward and lifted off.  The opto/mechanical
   assembly can then be removed from the tray.  Set the tray aside.  The
   mechanism shown in the photo of the Sony CDU-31/33A CDROM Optical Deck is screwed into the rubber shock mounts.

9. If you prop up the PWB and reconnect the flexible cable - note the
   orientation marks you made previously - you can then run the drive
   with full visibility of the mechanism and optics.  With a CD in place,
   there is no danger to you from the laser beam.  Just make sure the
   PWB cannot short to anything and that the whole affair cannot tip over.

Reassemble in reverse order.  Be especially careful reinstalling the
flex cable.  Make sure no wires are being pinched and that nothing is
obstructing free movement of the optical pickup.  This is actually
pretty easy for this drive.

  14.11) Sony Playstation (and other game machine) problems

The following information applies directly to the Sony Playstation but other
CD/CDROM based systems use similar technology.

Note that the Playstation (and other newer game machines) are programmed
to only work with discs released for the same country or general geographic
location in which it was purchased.  Thus, if you got a good deal on a used
system, you may now know why: it might only work with Japanese software! :-(.

I believe Sony has a flat rate ($100 or so) repair fee for these - probably
toss the guts and replace them - but this is barely justifiable for a $200
system.  Many complaints are similar to the following with symptoms of
marginal play of audio or game discs, skipping, erratic operation, etc.

Other service centers have both cheaper and DIY kits for Playstation repair.
For example, Video Specialties advertises a $45 flat rate and also sell a
repair kit they say will handle loading, skipping, and other optical pickup
problems.  I have no idea of its price or whether these claims are accurate.

  14.12) Playstation appears dead

(From: Jerry Jessop (jjessop1@home.com)).

Quick test for symptoms of no power:

With the Playstation top cover off and no CD installed press down on the door
switch. What should happen is the CD will not spin, but the laser pickup
should move up and down attempting to focus on a CD.

WARNING: Laser is exposed - don't stare into it!  See the section: "SAFETY".
--- sam.

If the above does not happen the following problems may exist, in order of

1. Door switch broken 

2. No 8 VDC to CD, usually a blown ICP "fuse" on the motherboard, or bad power

3. CD controller toasted (bad)

  14.13) PSX controller unreponssive

(From: Jerry Jessop (jjessop1@home.com)).

For no response from controller problems:

The controller port ICP (integrated circuit protector) is blown and you are
not getting 3.3 VDC to the controller ports. Check for continuity on each ICP,
they are near the front of the PCB just below the CD ROM ribbon cable. They
will have a 15, 20, 50 etc labeled on each. The one labeled as 15 is blown :).
It is an 800 ma fuse.

BEWARE of non-Sony approved peripherals as they blow these fuses, especially
non-Sony mem cards inserted with the power on.

  14.14) General problems reading PSX discs

"I have a Sony Playstation, it starts up OK as in power-up etc. But, insert a
 disk and it does not seem to want to read the TOC.  The disc spins up to speed
 and the laser goes through the motions of focusing, but then zilch, nada,
 no-zinks!  Funny thing is it seems to play audio disks correctly, but not
 Playstation game disks"

Of course, first clean the problem discs and lens.  See the relevant portions
of this document for instructions and other general troubleshooting tips.
All the usual problems of normal CD players and CDROM drives apply.

Note that in general, it may be possible to play music discs with few or no
problems and still not be able to reliably play games (or as applied to CDROM
drives, reliably access data).  Readout of programs and data must be totally
error free while errors can be tolerated for audio tracks with little or no
detectable degradation in sound quality.  Another reason is that audio is
always read at the 1X rate; the system may be more tolerant of a marginal
disc or servo alignment at the 1X compared to 2X or higher rate.

Some of these problems may actually be a result of poor design due to extreme
and unacceptable cost cutting on Sony's part.  After all, the Playstation
reader is essentially the same as a 2X CDROM drive - which should be mature
technology by now!

(From: Rusty Burke (rustyb@maritronix.com)).

A common problem on Playstations is the lens 'sled positioning' assembly.
The lubricant that they used on this gets 'a little' solid.

Solution: remove old lube (all the way back to the motor worm gear) and
use a long-lasting lubricant. I use a mixture of tri-flow and graphite
grease.  This seems to cure the problem.

Apparently what happens is that the CPU requests a read of a certain
sector of the CD, and the sled can't get the lens to the proper location
quickly enough.

(From: (mj1129@aol.com)).

A lot of Sony Playstation had this problem.  Sony knows this problem, and
they suggest to adjust the optic laser power to 1 V p-p (at the RF test
point) or change the optic.

CAUTION: adjusting laser power is always a risky operation.  Replacing the
optical pickup may not be a realistic option as Sony probably charges more
for the replacement part than for an entire Playstation! --- sam.

(From: Malik Dad (psxpic@goliath.mersinet.co.uk)).

Check the focus bias adjustment.  These machines are really very finicky when
it comes to laser alignment.

There are many machines out there with similar problems to yours.  This is
usually caused by a laser servo that has been badly set up. The symptoms are
jumping and/or skipping on the FMV (full motion video) intro sequences and
jumping and/or skipping on the music.  In the worst case, certain gold (CD-R)
discs will not boot.  The pits on CD-R are never as well defined as a pressed
disk resulting in around a 1/4 to 1/2 volt reduction in the RF eye pattern.

The problem can generally be cured by carefully adjusting the bias control
on the main board near the laser ribbon connector. turn this a little bit
clockwise or counter-clockwise until you have decent results. when you are
happy leave it alone.  It can be tempting to keep adjusting for different
disks trying to get it spot on.  There are not many machines that will play
every single gold disk perfectly.  Most will skip and jump occasionally no
matter how carefully they are tweeked.  DO NOT touch any other adjustments!

See: http://www.gpl.net/paulmax/psx for more info on Playstation modifications.

Not sure of which of the following it more appropriate.  Just make sure you
mark the original positions of the pots --- sam.

(From: Mike Walker (vdospec@werewolf.net)).

Caution: for the following, I would avoid touching the pot on the pickup itself
unless you have exhausted all other possibilities - this is laser power and
can easily result in a ruined laser --- sam.

Sony will not give out any procedure, we have done it before many times...

As far as the beam, the adjustment is on the CD sled itself right by the eye.

The gain is located on the main board listed as gain, don't mess with the bias
adjustment, try moving the gain about 1/8 inch or less clockwise, then check
the play of your CD's, most of the time this takes care of the problem, if not
try moving the beam focus about the same and same direction.  Not to much on
either it's been known you can burn out the laser.

We like to mark our original postion with a red marker pen, you can lose
where you were and really goof it up.

Use ESD precautions, the laser is sentitive to static also.

Also, try and replace the grease on the gear drive also, we have found that
this helps a great deal also.  Remove old, use new lubriplate or similar.

(From: Jerry Jessop (jjessop1@home.com)).

You have it backwards, adjust the Bias and leave the gain alone. If
you set the bias level on wiper of the Pot to around 1.60 vdc with a
CD loading that is "generally" a good figure. Now adjust the gain
during an FMV sequence until it stops reading at one extreme.  Then
the other, and set it in the middle. Regrease the rails using "LaBelle
106" a white grease with teflon designed for plastic components found
in hobby stores.

Of course more than likely the optical sled has groves worn in it and
now the laser azimuth is out of alignment.  The only solution is to replace
the entire pickup assembly.  MCM claims to be getting a new shipment of
Playstation optical pickups soon - their price is $39.95 (as of November,

(From: Cyberchaos (cyberchaos@aol.com)).

All earlier productions of the playstation utilized a plastic sled rail
construction which collapses and causes this problem. These must be replaced
with the upgraded steel versions. Cleaning is a very short term cure.

  14.15) Bouncing picture on some (Zenith) TVs

The problem of a shaking picture on some TVs (notably, Zenith models) is due
to a problem in the PlayStation sync generation, not really a TV failure.

(From: Jerry Jessop (jjessop1@home.com)).

PlayStations will sometimes slowly  "bounce" on older Zenith chassis sets,
this is due to the way the vertical sync is outputted on the PlayStation.

Call the PlayStation 'hotline' and explain the problem, it is well known and
the system will be modified at no charge to you and you will get a free game
for your trouble!

A small daughter board will be installed that will correct the problem.

Chapter 15) Testing of Optical Pickup Assemblies

  15.1) Introduction

Identifying front-end problems in CD players, CDROM drives, laserdisc players,
and other optical drives is often thought to be a mysterious and difficult
task.  This section describes basic techniques confirming functionality of
the laser diode, focus voice coil actuator, tracking voice coil actuator, and
photodiode array.  No exotic test equipment is required.

It is strongly recommended that you read and become familiar with the other
information in this document.  For general optical pickup information, see
the section: "CD optical pickup operating principles".  For a description
of some common types, see the section: "Sony KSS series optical pickups".

Don't immediately conclude that your problem is in the optical pickup.  It is
likely elsewhere and you will not need to undertake the testing described

If the unit is able to read the disc directory, if even erratically, then
these tests are unnecessary (unless you suspect an intermittent in one of
these subsystems) as all of major parts of the laser pickup assembly must be
properly functioning in order to do this.  However, this does not guarantee
that there are not some marginal components such as a weak laser diode or
shorted turns in the focus or tracking coil - more on these problems later.

Don't ignore the trivial: have you cleaned the lens?  Sometimes a dirty lens
will result in symptoms that may be mistaken for much more serious problems.

For intermittents, first carefully inspect the pickup assembly for bad solder
connections and hairline cracks in the flexible printed cables.  Interlock
switches may be dirty or worn.  Mechanical problems may result in intermittent
behavior as well.

  15.2) When and why to test the pickup

If you have examined the 'RF Test Point' with a scope and found a proper 'eye
pattern', then as noted, these tests are not needed as this indicates proper
functioning of all the major components of the optical pickup.  If, however,
any of the following are observed, then testing of the laser diode, focus and
tracking actuators, and/or photodiode array is suggested:

* The startup sequence does not complete due to obvious failure of the pickup
  to perform some action.  For example, there is no attempt to focus.

* Focus appears to be established but the directory is never displayed even
  though the disc spins at the correct speed - or overspeeds or does not spin
  in correct direction (clockwise as viewed from the label side is correct for

* The 'eye pattern' is weak, distorted, or missing at the RF test point.

Try to eliminate alternative causes before undertaking these tests as there is
a slight chance of damage due to accidents or electrostatic discharge.

Will it be worth the time and effort?  Only you can decide how much your time
is worth.  There is a good chance that these tests will only confirm that the
pickup is dead - not many of the faults you will be able to locate have easy
fixes.  You will learn something if that matters.  However, with the cost of
new single disc CD players less than $70 and changers less than $100, any
rational analysis of the expected value for this undertaking may recommend the
dumpster.  But, we all know that hobbiest's time is not worth much - as in

The descriptions below assume that the pickup is still installed in the player
but selected portions are disconnected when required.  This enables us to
conveniently use the circuitry of the player to control certain functions for
the 'live' laser diode and photodiode tests.

It is also possible to test the pickup stand-alone but this will require an
alternative power supply to drive the laser diode.  Since the microcontroller
will not be imposing its own will on those parts of the pickup still connected
to the player, this may be preferable.  However, if you are uncomfortable in
providing a substitute power supply for the laser diode, then leave that
function to the player.

Caution: whenever applying external power to any component, totally disconnect
it (by unpluging or unsoldering - label each wire if there is any ambiguity)
to prevent damage to the circuitry on the logic board.

  15.3) Required tools, documentation, and test equipment

Only a minimum of tools and test equipment are required for these
testing techniques to be effective.   An oscilloscope is desirable but a
VOM or DMM can substitute in a pinch since no high frequency measurements
are needed.  However, we will assume a scope is available.  This section
does not address mechanical problems in the sled drive, or the drawer or
spindle motors.  These problems are adequately handled in the elsewhere
in this document.  It is assumed that these components have been verified
to be functional as there correct operation may be required for some of the
tests described below.

A schematic will help greatly if available.  Depending on the design of
the unit, you may be able to infer enough about the front-end electronics
to get away without one.  The design of the components of the optical pickup
are sufficiently similar among manufacturers to make the tests relatively
model independent.  What may differ are polarities of photodiodes, laser
diodes, connector pinouts, etc.  These can usually be determined fairly

Despite the incredible precision of the focus and tracking servos, we
can perform meaningful tests without sophisticated or specialized
test equipment.

Also see the sections: "Troubleshooting tips" and "Test equipment".

The following tools and test equipment will be required:

1. Basic hand tools including precision jeweler's screwdrivers.

2. A VOM or DMM.

3. An oscilloscope (for photodiode/RF tests).  For most of the tests,
   almost any scope will do as long as it has a DC coupled vertical amp.
   As noted above, a scope is not essential but is highly desirable.

4. A 0 to 5 volt variable DC power supply (400 mA).  The power supply can
   be a 4-5 V 'wall wart' with a Variac.  Alternatively (but not as
   desirable),  you can use a fixed 5 V supply with a series adjustable
   resistor (100 ohms for focus and tracking actuator testing, 250 ohms
   for laser diode testing).  A highly regulated supply is not needed.

5. Resistors: 22 ohm 1W, 5 ohm 1W, 50 ohm, 1 M ohm.

6. Assorted test clip leads, a few feet of #24 solid hookup wire (RS232
   quad or multiconductor phone cable is good source).

7. IR detector circuit, IR detector card, or IR sensitive camcorder (for
   laser diode tests).

8. (Optional) Slow speed sweep or function generator (1-10 Hz) with
   low impedance output or amplifier, see text.

For the following discussions, a component CD player is assumed to be
the unit under test.  Make appropriate adjustments in interpretation
if it is a portable CD player, CDROM drive, or optical drive.

  15.4) Precautions

Reread the section: "SAFETY" for your own protection.

To minimize the chances of damage to the laser diode - which is extremely
sensitive to static and excess current - leave its connector plugged
into the main board as much as possible and do not attempt to test the
laser diode with a VOM (which on the low ohms scale may exceed the current
rating of the laser diode - poof, even if only for a microsecond.

As with all modern solid state equipment, preventing electrostatic discharges
to sensitive components is critical.  An antistatic wrist strap is desirable.
In any case, work in an area where static is minimized - not on a carpet
prone to static.  Make it a habit to touch the metal chassis first to
discharge yourself.

  15.5) Basic description of optical pickup

Also see the more detailed description (including a diagram) of the typical
optical pickup components and operation found in the section: "CD optical pickup operating principles".

In order for information or music to be read off of a CD, several systems must
work closely together:

1. Laser must be emitting a coherent beam of sufficient power and stability.
   Optical system must be clean and properly aligned.  Laser power is
   maintained constant via an optical feedback loop controlling laser diode
   current.  Therefore, a weak laser may not be salvageable as the feedback
   loop may have done all that is possible.

2. Photodiode sensors must be functioning correctly for data recovery
   and focus and tracking feedback.  In a 'three-beam pickup', there are
   six segments: the central segments A-D are used for focus and data
   recovery; the outer segments E and F are used for tracking feedback.
   In a 'single-beam pickup' segments E and F are omitted.

3. Lens must be focused to within a fraction of a um of optimal to
   produce a diffraction limited spot.  This is less than 2 um in diameter at
   the disc 'pits'.  The lens is actually positioned several mm from the
   disc surface and is maintained at the correct distance through optical
   feedback controlling the lens position using the focus coil.  Note:
   um = micrometer = 10E-6 meter; mm = millimeter = 10E-3 meter.  1 meter
   is 39.37 inches.

4. Lens must align to within a fraction of a um of the center of the track.
   Tracks on a CD are spaced 1.6 um apart.  Tracking is maintained via
   optical feedback controlling the radial lens position using the tracking
   coil (or radial positioning unit on some rotary positioners).

Note that if the behavior while the CD player is attempting to read the
directory changes whether a disc is in place or not, (and there is no
separate disc sensor), then some or all of these components are functioning
correctly.  For example, many CD players will not attempt to rotate the
spindle until proper focus has been established.  Thus, if the CD rotates
when in place but the bare spindle does not, it is likely - though not
guaranteed - that focus is being established successfully.

  15.6) Identifying connections to the optical pickup

In order to perform many of the tests described below, you will have to locate
the drive and/or signal connections to the optical pickup. While there are
many variations on the construction of optical pickups even from the same
manufacturer, they all need to perform the same functions so the internal
components are usually quite similar.

Here is the connection diagram for a typical Sony pickup:

               R1                  +---|<|----o A   |             +----o F+
            +-/\/\---o VR          |      PDA       |            (  
       PD1  |   |                  +---|<|----o B   |            (    Focus
   +---|<|--+---+----o PD (sense)  |      PDB        > Focus/    (    coil
   |                               +---|<|----o C   |  data      (
   |   LD1                         |      PDC       |             +----o F-
   +---|<|--+--------o LD (drive)  +---|<|----o D  _|
   |       _|_                     |      PDD      _              +----o T+
   |       --- C1                  +---|<|----o E   |            (
   |        |                      |      PDE        > Tracking  (  Tracking
   +--------+--------o G (common)  +---|<|----o F  _|            (    coil
                                   |      PDF                    (
    Laser diode assembly           |                              +----o T-
                                   +----------o K (Bias+)
    (includes LD/PD and                                        Focus/tracking
     flex cable with C, R).       Photodiode chip                 actuators

The laser diode assembly and photodiode chip connections are typically all on
a single flex cable with 10 to 12 conductors.  The actuator connections may
also be included or on a separate 4 conductor flex cable.  The signals may
be identified on the circuit board to which they attach with designations
similar to those shown above.  The signals A,C and B,D are usually shorted
together near the connector as they are always used in pairs.  The laser
current test point, if present, will be near the connections for the laser
diode assembly.

It is usually possible to identify most of these connections with a strong
light and magnifying glass - an patience - by tracing back from the components
on the optical block.  The locations of the laser diode assembly and photodiode
array chip are usually easily identified.  Some regulation and/or protection
components may also be present.

Note: There are often a pair of solder pads on two adjacent traces.  These
can be shorted with a glob of solder (use a grounded soldering iron!) which
will protect the laser diode from ESD or other damage during handling and
testing.  This added precaution probably isn't needed but will not hurt.  If
these pads are shorted, then there is little risk of damaging the laser diode
and a multimeter (but do not use a VOM on the X1 ohms range if it has one) can
be safely used to identify component connections and polarity.

  15.7) Testing the laser diode while in the player

Without a laser power meter, it will be difficult to fully verify laser
functionality.  However, determining that IR is emitted will provide a
reasonable assurance of laser operation.

For this test you will need an IR detector.  A simple circuit is described
in the section: "IR detector circuit".  This unit is also useful for testing
of remote controls and other IR emitters.  You can also use an IR detector
card - available at an electronics distributor.  In a pinch, CCD based
camcorders are often sensitive to IR.  It will appear as a bright spot if
the laser beam is projected onto a white paper screen.  However, you will
probably need 3 or 4 arms to position the screen, push the play button, and
hold the camcorder while attempting to view the detected spot through the

You will need to gain access to the lens.  This may require the removal
of the clamper assembly.

Once this is accomplished prepare to position the photodiode of the
IR tester within 1/8" of the lens.  Plug the unit in and turn it on.
On portables, you will need to defeat the door interlock - use a toothpick
or bit of cardboard.  Sometimes a CD player will have a disc detect sensor
separate from the laser assembly - this will need to be defeated in order
for this test to work without a CD in place.  If it is a simple optical
sensor, a piece of black tape or paper should suffice.

The first thing that should happen once a CD is in place and the play
button is pressed is for the laser to be powered.  You should be able to
detect this in a darkened room because there is usually a very faint
red appearing emission which you can see as a tiny red dot of light
if you look at the lens from a safe distance of at least 6 inches at
an oblique angle (WARNING: Do not look directly into the lens from directly
above as the invisible IR is much stronger than the faint red emission and
potentially hazardous).  If you see the faint red light, you know that at
least power is being applied to the laser diode.

With the laser lit, the lens should go through a few focus search cycles -
between 2 and 8 typically.  While it is doing this, position the IR detector
above the lens.  If the laser is working, you will get a positive indication
of IR in about a 30 degree cone on either side of the lens.  While you
have no way of knowing if the power output is correct, this is a reasonable
indication of laser operation.  Due to the wide angle of the beam, the
power decreases rapidly with distance so you will need to be very close
to the lens for a positive result.

Note that if the lens moves smoothly in at least one direction (up or
down), you have also confirmed that the focus actuator is functional.

If the IR detector does not pick up a beam and you do not see the red dot,
then either the laser diode is really dead or there is no power being applied
by the control circuits.

At this point, you have four options:

1. You can give up.  However, you would not have gotten this far if you
   were likely to be defeated so easily.

2. You can attempt to obtain a schematic if you do not already have one
   so that you will be able to test the control circuits to determine if
   the laser diode is being powered.

3. You can attempt to trace the laser power circuits in the hope that you
   will find something absolutely obvious that is amiss - a bad connection
   or open resistor, for example, resulting in no power to the laser diode.

4. You can perform some simple but risky tests on the laser diode itself
   in an attempt to light it from an external power supply.  As noted 
   below, laser diodes are easily destroyed and you will have no warning.
   One nanosecond it will be a laser - the next it might be a DED - Dark
   Emitting Diode.

  15.8) Testing the laser diode with an external power supply

Consider the following only if there is no indication of laser output
while connected to the player and you do not have schematics or a service
manual to determine if the laser power circuits are functional.

Typical currents are in the 30-100 mA range at 1.7-2.5 V.  However, the power
curve is extremely non-linear.  There is a lasing threshold below which
there will be no output.  For a diode rated at a threshold of 30 mA, the
maximum operating current may be as low as 40 mA.  A sensing photodiode is
built into the same case as the laser diode to regulate beam power.  It is
critical to the life of the laser diode that under no circumstances is
the safe current exceeded even for a microsecond!

Laser diodes are also extremely sensitive to electrostatic discharge, so use
appropriate precautions.  Also, do not try to test them with a VOM which
could on the low ohms scale exceed their safe current rating.  Even
connecting the test leads can blow the laser diode from static on a bad day.
In addition, always make or break power or test connections with the player
turned off.

Locate the laser power connector by tracing back from the three pins on the
laser diode assembly.  Note: the following only applies if the laser diode
is directly connected to the cable.  If the power regulating circuit is
on the pickup, you will need to trace its circuit or obtain the schematic
as there are now too many variations to recommend a specific procedure.

Use the 0 to 5 VDC linear supply (a switching supply may put out laser diode
destroying pulses) with a 50 ohm resistor in series with the diode.
This is preferred over the variable resistor power supply as there is less
likelihood of any potentially laser destroying overshoot or noise.  If
you do use the variable resistor, make sure it is at its maximum resistance
when you start and that this is sufficient to keep the current under 20 mA.
Keep in mind that a wall wart rated at 5 V may actually put out 8 V or
more when unloaded - check the current into a short circuit before
connecting the laser diode.

Slowly bring the current up until you get a beam. Use an IR detector for
this!  If you get the polarity backwards or are actually measuring across
the internal photodiode, the voltage across the diode will go above 3 volts
or will be less than 1 V.  Then, turn power off and reverse the leads.
Note: some laser diodes will be destroyed by reverse voltage greater than
3 V - a spec sheet will list the reverse voltage rating.  The ones I have
tried out of CD players were fine to at least 5 V in the reverse direction.

Without a laser power meter, however, you will have no way of knowing when
the limit on safe beam power (safe for the laser diode, that is) is reached.
For this test, increase the current only until you get an indication on
the IR detector or you see the red dot.  You are not trying to measure power,
just to see if it works at all.  A typical threshold is around 30 mA.
Sometimes, the operating current is marked on the pickup.  If this is the
case, do not exceed this current.

If you detect a beam and there was none before, then your problem is most
likely located in the player's control or power circuits, not in the pickup.

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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]