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


  15.9) Laser power adjustment

If you have the service manual and it provides a procedure not requiring
a laser power meter (which you probably do not have), then by all means
follow that procedure.

As noted elsewhere, it is possible to destroy the laser diode by attempting
to adjust its output power.  However, if you suspect a weak laser as indicated
by noisy playback or poor tracking performance (not a dead one as this will
not help), and have exhausted all other possibilities such as the servo
adjustments - and feel you have nothing to lose, you may attempt one of the
procedures described below (with some risk) to determine if the laser diode
is at fault.

The following requires that you can play a disc - even if it has some problems
with noise or tracking.  This is best done with an oscilloscope.  However, if
you do not have one, you can still try the procedure.  The risk is that without
a visual indication of the signal amplitude, you will turn the control too far
before you realize it and destroy the laser diode.

* If you have an oscilloscope, put a probe on the RF test point.  While the
  disc is playing, you should see the eye pattern.  Mark the exact amplitude
  of the peaks.  Also, note the 'playback quality' so you will recognize if
  it changes.  Note: while the correct voltage for the eye pattern is not the
  same in all players, typical values are in the 1 to 2 V range.  If you see
  a few hundred mV or less, there is likely a problem.  Caution: a weak eye
  pattern can also be due to improper focus bias adjustment (check it) or an
  electronic problem.  The laser power may be normal.

  It may be safer to turn the laser power adjustment with player power off
  to avoid the possibility of electrical noise causing current spikes.  Your
  choice.  Mark the exact position of the laser power adjustment so you can
  get back to it if there is no effect or it makes things worse.
  Turn the control the slightest amount clockwise.  Caution: this control
  may be very sensistive - 'slightest' really does mean just a very small
  amount.  Turn power back on and/or note the eye pattern amplitude.  If the
  laser diode is not at the limit of its power and thus bad, you should see
  the amplitude change from what it was.  If it has decreased, try the other

  Note the playback quality.  Has it changed any?  If not, then laser power
  is probably not your problem.  If the amplitude of the eye pattern is
  unchanged, you either are turning the wrong control or the laser is at its
  power limit - and probably near the end of its life.  Try the same test in
  the counterclockwise direction if the amplitude decreased - not every
  designer knows left from right.

  If there is improvement, you can risk leaving the control at the new (most
  likely) higher power setting realizing that you may be shortening the
  ultimate life of the laser diode.  Do not push your luck by continuing to
  turn up the power unless you have exhausted all other alternatives.

* If you do not have an oscilloscope. you can still attempt the procedure
  above, using audio listening exclusively to determine if there is any
  change.  It is just a little bit riskier.  As noted, the laser power
  adjustment may be very sensitive you will have no direct way of knowing
  how much you have increased the setting.

  15.10) Testing the focus and tracking actuators

If there is a question of whether the lens is focusing or tracking properly,
perform the following.  Again, if the unit is able to read the disc directory
at all, then these tests are not needed.  Note that if you have a CD player
with a rotary positioner, there may be no separate tracking coil as coarse and
fine tracking may be combined.

Typical linkages between the lens/coil assembly and the body of the pickup are
(1) a sliding shaft (focus) and rotation on the shaft (tracking) or (2) a
hinged-hinge.  With (1), the slide can get gummed up preventing reliable focus
and tracking.  With (2), one or both hinges can break - they are often made of
thin flexible plastic. Repair is not really possible.

First, identify the cable leading to the focus and tracking voice coil
mechanism.  This is usually a 4 conductor cable separate from the data and
laser cable (at least at the pickup end).  Disconnect it from the mainboard
before testing.  Using a DMM or VOM, you should be able to locate a pair of
coils with very low resistance - a few ohms.  One of these is focus coil and
the other is the tracking coil.

Construct one of the following test circuits:

1. Your 4-5 V DC wall wart plugged into a Variac with its output connected to
   a 22 ohm 1W resistor in series with a pair of 2 foot #24 insulated wires.

2. Your 5 V DC power supply connected in series with the 100 ohm variable
   resistor and 22 ohm 1W resistor with a pair of 2 foot #24 insulated wires.

Gain access to the lens for visual inspection.  This may mean ejecting
a disc, opening the drawer, or in some cases, actually removing the
clamper.  In a portable or boombox, the lens will be readily accessible.
Unplug the CD player from the wall or remove the batteries - you will not
be using its internal power.

Locate one pair of the two pairs of low resistance connections you identified
above.  With your power supply off or the Variac turned all the way down,
connect the #24 leads to one of these pairs.  Now, turn on the power and
slowly adjust the Variac or reostat while watching the lens.  If you are
connected to the focus coil, you may see the lens moving up and down.  If
you are connected to tracking coil, you may see it moving from side to side.

If there is no motion, turn off the power supply, reverse the polarity and try
again.  For a typical pickup, the 4-5 V power supply and minimum of 22 ohms
should cause the lens to move through the entire range of motion up and down
or side to side as appropriate. Once you have exercised the first coil, switch
connections and repeat for the other.  If the motion is jerky, the lens
assembly may be dirty.

Clean it carefully first with a bit of compressed air (not high pressure, a
photographic air bulb is fine) and then with Q-tips and isopropyl alcohol.
Do not lubricate.  Repeat the tests after the cleaning.

If both the tests are positive, you have confirmed operation of the focus and
tracking actuators.  If either you were unable to locate both pairs of coils
or one or both actuators did not move, then you have located a problem.  An
open coil can be due to a cable problem or a break at the coil.  If the break
is right at the solder connections which are usually visible once the plastic
protective shroud is popped off, then it may be possible to repair it.  This
will require a great deal of manual dexterity and patience - the wire is really
really fine.

It is still possible for there to be shorted turns in the fine coils or an
intermittent that was not detected.

* Shorted turns would reduce the frequency response of the servo, reduce the
  reliability of focus or tracking, and increase the needed servo driver power.
  A CD player that is overly sensitive to slight disc defects even after all
  the proper adjustments have been performed may conceivably be a result of
  this type of fault.  An additional symptom may be an unusually hot servo
  driver IC.  However, many of these ICs run hot normally so don't panic as
  the possibility of shorted turns is really quite remote.

* An intermittent may only show up during dynamic operation or with certain
  particularly finicky CDs or other peculiar circumstances.  The intermittent
  could be at the solder connections or the fine printed ribbon cable that
  connects the moving lens assembly to the remainder of the pickup.

  15.11) Testing the photodiode array

The photodiode array in a optical pickup consists of an IC with typically
4 or 6 detector segments.  Four segments may be used for the less common
'single-beam pickup' while 6 segments are used in the 'three-beam pickup'.

These segments are usually designated A-F.  A, B, C, and D are the main
detector which is used for both focusing and data recovery.  Segments
E and F are used in a 'three-beam pickup' for fine tracking feedback.

We will assume a three-beam pickup for the remainder of this discussion.

All 6 photodiodes are connected to a common point which during operation
has a DC bias voltage on it typically around 5 V.  If they are connected
common anode, it will be negative; if common cathode, it will be positive.
The reason is that the photodiodes need to be reverse biased for normal
operation.  The outputs of the photodiodes feed several operational
amplifiers which are set up to amplify the current from the photodiodes.
The normal connections may be at virtual ground potential or they may
feed into large value resistors.

The connector to the photodiode array is usually separate and will typically
have at least 8 wires - photodiodes A-F, ground, and bias voltage.

You will need to identify the wiring.  First locate the ground using the
ohmmeter.  Then locate the bias - it will probably go to a low value
resistor and then to the supply.  Another way to identify the bias wire
is to turn on the player and measure each of the possibilities.  The bias
will be the highest or lowest and will be solid with no noise or ripple.
It will probably be powered all the time.

Now for the photodiode segments.  Very often the connections or some of
the connections are marked on the circuit board.  For example, there may
be several labeled test points designated A+C, B+D, E, and F.  Since
the A and C segments and B and D segments are usually shorted together
on the circuit board, this provided all the info needed to identify the
photodiode connections.  It is not important to distinguish between A and C
or B and D for the following tests though you will want to be able to
separate them.

With power off, there is essentially no light on the photodiode array.
Unplug the photodiode connector from the main board.

Using your ohmmeter, test each diode for opens and shorts as you would
test any signal diode.  There should be a junction drop in the forward
direction and very high resistance in the reverse direction.  If you are
using a DMM with a diode test mode, the junction drop will typically
measure .7-.8 V.  There may be a very slight difference between the readings
for segments A to D and those for E and F.

An initial test of photodiode response can be made using an external light
source - a flashlight or other incandescent bulb or IR remote control
shining into the lens from directly above.  With the multimeter connected
to reverse bias each diode segment, shine the light into the lens.  The
resistance reading should drop somewhat - possibly dramatically.  Segments
A to D should show reasonably similar sensitivities but these may differ from
segments E and F (which should be similar to each other).

Similarly, with with the photodiode connections restored to normal, you can
use an oscilloscope to monitor the RF test point.  A source of IR directed
into the lens from above may result in a detectable change in the signal - but
only when the photodiode array is properly biased.  This may be all the time
that the CD player is turned on or only when it is trying to focus or perform
some other operation.  With an IR remote, you should actually see the pulsed
signal for each key-code.  On a typical Sony CD player, I was able to get about
a .1 V signal at the RF test point using a VCR remote control as an IR source.

However, even on a functional pickup, due to the nature of the optics, these
responses may be very weak or undetectable.  Thus, failure of either of the
above tests is not strong evidence of a bad photodiode array.

Any unusual readings such as a significantly lower resistance for one of the
diodes, a short or open of a particular diode, a short between diodes, or
variations in sensitivities is an indication of a problem.  While it is
possible for there to be a cable or soldering defect, this is somewhat
unlikely though bad solder connections or breaks in the flexible cables
are not out of the question.

A defect found in the photodiode array will usually mean that the laser
pickup is not salvageable with reasonable effort.  Even if you could locate a
replacement photodiode array, aligning and soldering the (most common)
surface mount package would be quite a challenge without the factory jigs.

Assuming these tests do not turn up anything, the next step will verify that
the photodiodes are picking up an optical signal and will evaluate the
relative strengths of each segment using the laser diode, optical system,
and disc combination.  Note that for these tests to confirm proper operation,
the optical alignment must also be correct.

For the tests using the internal laser diode, we will need to setup one
of the following.  Method (2) is more straightforward but requires the
optional signal generator for best results.  In each case the objective is
to cause the lens-disc distance to sweep through perfect focus without
requiring that the focus servo loop be closed.  This will then result in
a signal that will include the point of maximum signal amplitude on a
periodic basis.  Alternative methods may be used to accomplish the same

Both techniques require the adjustable power supply previously used to test
the focus coil.

1. Adjustable focus with continuously rotating spindle.  For the spindle
   motor, you will need a 1.5 V battery or your power supply with a suitable
   series resistor to cause the spindle to turn at approximately 1-2 Hz
   (rps).  Warning: disconnect the motor from the mainboard!  The unavoidable
   wobble of any disc is essential in this case and will sweep the focus
   distance by more than enough to cover the entire focus range of interest.

Note: this assumes that the spindle is driven by a conventional PM DC
motor.  If it is a brushless DC motor, then some of the control electronics
may be external to the motor and you will not be able to just provide a DC
voltage to get it to rotate.  If this is the case, you must use method #2.

2. Stationary spindle but sweeping focus.  This is the better method but
   requires a signal generator for easiest use.  You can do this
   by hand using a Variac or reostat (this is easier if you have three
   functioning hands).  A better method is to use a 1-10 Hz sinusoid or
   triangle wave from a low frequency signal generator with a low impedance
   output or feeding an emitter follower or audio amplifier to boost the
   current.  This signal is then fed into the coil along with the focus
   offset derived from your power supply.

Note: it may be possible to dispense with these test setups and just
use the normal focus search of the CD player to provide the sweep.  However,
since we will be interfering with the proper feedback by removing selected
sensors, there is no telling what the microcontroller will do.  Therefore,
breaking the feedback loop as we are doing is preferred.  If the CD player
appears to make many attempts at focus, this may be worth a shot, however.

You will also need a disc - preferably one you do not care much about as
sometimes it will get scratched due to opening the drawer accidentally or
something equally idiotic while the disc is still rotating.

Locate a 1 M ohm resistor and securely fasten it to a ground near the
photodiode connector.  Put your scope probe on the other end with its
ground clipped to the same ground point as the resistor.  Bend the free
lead of the resistor completely over so that it will be able to hold the
end of a wire like a mini-clip lead.

Make sure you remember or mark down exactly how the connector is wired
so that as you remove individual wires, you will be able to get them
back in the proper spot.  Presumably, you have already made a diagram
of the photodiode connector wiring.  Component players often have connectors
with individually removable socket pins.  A fine jeweler's screwdriver or
paper clip may prove handy in removing these one at a time.

Turn on your power supply and adjust the focus to about midrange.
Start the spindle rotating or turn on the signal generator to provide a
small sweep - about 1/10 V p-p as measured on the coil should be fine.

  15.12) Making the photodiode measurements

Remove the wire corresponding to the photodiode (say, A) to be tested from
the connector but leave the connector itself plugged into the main board.
Set the scope for 1 V/div. vertical on a slow free running sweep.

Clip the A wire into the resistor.  Now, turn on power to the CD player.
While the player thinks it is focusing, slowly adjust the focus voltage
while observing the scope.  As you approach proper focus, you will see
the signal increase (depending on polarity) greatly, pass through a maximum,
and then decrease.  Depending on the design of the CD player, you may need
to turn it off and on several times before you locate the signal as
the microcontroller may give up pretty quickly with no focus or tracking
coil servos (since you disconnected the actuators).  If you have the service
manual it may tell you how to force the laser to be powered all the time.
Leave the focus set near the middle of the region of high signal.

If you are using the signal generator to perform the focus sweep, you
may need to optimize the amplitude of the signal by adjusting the signal
generator output and offset from your power supply.

You probably should not need to touch the settings for the remaining
photodiode segment tests.

Repeat the above procedure for each of the photodiodes A-F.  All should
produce fairly similar signals, say within 20 % of one another in amplitude.
If A,B,C,D or E,F differ from one another by more than say, 20 %, there may
be a serious optical alignment problem in the pickup (the player may have
been dropped or bounced around without securing the hold-down screws, if
any).  Alternatively, the photodiode array may be bad.  It is also possible
for there to be partially shorted photodiode segments in which case, the
outputs will not be independent as they should be.  Loading one segment's
output with a resistor may affect the output of one or more other segments.

In any of these situations, such a discrepancy in A-D will prevent the
establishment of proper stable lens position at the optimal focal distance.
This will prevent the formation of a proper 'eye pattern' and subsequent
data recovery.  A significant difference between E and F (beyond the
adjustment range of the tracking or E-F balance control) will prevent proper
tracking.  Note, however, that the signal amplitude from A-D and E,F may
differ as A-D operate off of the main beam and E,F operate off of the
first order diffracted beams which are weaker.  As with the basic photodiode
tests above, a failure here usually will require the replacement of the entire
optical assembly.

As noted, if the pickup's optical alignment is way off, there could be
significant differences in photodiode responses.  On component type units,
it is unlikely that the optical alignment would shift on its own.  Portables
that have been dropped or automotive units subject to constant bumps
and vibration could have alignment problems, however.  If this is your last
hope, then some experimentation with adjustment of the optical alignment
on a successive approximation basis might be worth the effort.  Mark the
original position of any adjustments and try small variations on either
side to determine their effect.  You might get lucky.  If this eventually
results in improved uniformity of photodiode response, alignment may be
the problem.  If you can more or less equalize the response, reconnect the
servos and attempt to get an eye pattern.  If you can, optimize the eye
pattern stability and amplitude using the optical alignment adjustments
and servo adjustments.

  15.13) Sony KSS series optical pickups

Note: For general information on optical pickups see the section: "CD optical pickup operating principles".

These are probably the most common optical pickups in the universe.  Many
variations - many dozens if not hundreds - on the basic design have been
produced from before 1988 until the present.  In general, they are compact,
simple, robust (despite what you may have heard), and no doubt dirt cheap to

Depending on the type of player and mechanical constraints, the specific
optical arrangement and construction will differ.  Many brands of CD players
and CDROM drives actually use Sony pickups.  While these are all recognizable
for their octagonal black lens cover and parallelogram type lens suspension
for focus and tracking (neither of which has changed noticeably in 10 years),
the construction of the fixed optics has gone through quite an evolutionary

* Early KSS pickups were quite complex with most of the components described
  in the section: "CD optical pickup operating principles" mounted as separate
  components.  These had accessible optical alignment adjustments and were
  also quite large and bulky compared to today's pickups.  An example of one
  of these is the Sony KSS110C Optical Pickup.

* Most of the KSS pickups found in consumer CD players and older CDROM drives
  combine some optical elements and eliminate others.  For example, types like
  the very common KSS361A do not have a separate collimating lens or
  cylindrical lens.  All parts are totally glued at the factory so no possible
  optical alignment adjustments are possible.

  A diagram showing the organization of the Sony KSS361A optical pickup is
  available in both PDF and GIF format.

  * Get CDKSSP: cdkssp.pdf or cdkssp.gif.

* The newest KSS series pickups appear to have combined the laser diode and
  photodiode into a single package.  They are offset by a very small distance
  so the outgoing and return beams pass through the same optics and thus there
  is no longer a beam splitter - more cost reductions!  By eliminating the
  optical components for redirecting the two beams, performance should also be
  better since this operation was not 100 percent efficient and additional
  optical surfaces can only degrade the beam quality.  The small reduction
  in the clarity of the detected analog signal resulting from the very slight
  non-perpendicular (with respect to the disc 'pits' surface) beams should be
  more than made up for by these simplifications.

  While I do not yet have a sample of a Sony pickup of this design, the
  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 the diffraction
  grating and turning mirror.  I expect that Sony versons are similar.

The description below is for pickups similar to the KSS361A and KSS210A.
These are horizontally organized and less than 1/2 inch thick.  The laser
diode, grating, and beam splitter are mounted inside the casting of the
optical block.  The turning mirror is glued to its base plate, the photodiode
array is glued to a port on its side and the objective lens and its focus and
tracking actuators are mounted on a self contained removable unit.

Please refer to the closeup views of the Sony KSS361A Optical Pickup.

The following can be seen from the underside after removing a cover plate (1
screw).  The descriptions are for the outgoing beam which originates at the
laser diode, passes through the diffraction grating, then reflects from the
dichroic beam splitter mirror on its way to the objective lens:

* Laser diode.  This is clamped and glued in place in a nicely finished brass
  barrel which is itself clamped and glued in place in the optical block.  An
  adjustment for optical power sensitivity, is mounted on the flex cable next
  to the laser diode.  This may mean that identical model pickups should be
  interchangeable without laser power adjustments - hopefully.  Many players
  don't have a laser power adjustment pot on the electronics board.

  The front face of the laser diode package is angled so that the exit window
  (anti-reflection coated) is also mounted at what may be the Brewster angle,
  probably to further prevent stray reflections from the window's surfaces
  from feeding back into the laser diode's cavity or interfering with the
  detected signal.  (At the Brewster angle, light polarized parallel to the
  window is totally reflected and light polarized perpendicular to it is
  totally transmitted.  The output of these edge emitting laser diodes is

  The Closeup of Laser Diode from Sony KSS361A Optical Pickup shows the
  angled front face and optical window.  The reason it appears so HUGE is that
  the photo was scanned at 600 dpi - this is not a monster laser diode!  It
  can be seen more like 'actual size' in the upper left corner of the group
  photo, A Variety of Small Laser Diodes.

* Diffraction grating.  Glued onto the end of the barrel in which the laser
  diode is mounted.  The grating is at a 45 degree angle to produce the 3
  spots for tracking in the appropriate orientation.  (Once reflected through
  the lens the spots are in the direction tangential to the tracks).

* Collimating lens.  On some versions, there is an actual collimating lens.
  However, the most common models do not appear to have one.  There is nothing
  really wrong with such a design, it is just unexpected.  Their optical
  efficiency will be lower since some of the beam will be lost to the side
  walls but other than that, a shorter focal length objective lens should be
  able to compensate fully for a non-parallel beam.  The optical path is so
  compact in these pickups that the losses are likely to be small.  It is also
  not clear why otherwise very similar model pickups in very similar model CD
  players differ in this respect.

  A test of the laser diode barrel assembly removed from a KSS361A pickup
  shows that its output is an ellipsoidal beam with a divergence of at least
  10 degrees on the narrow axis (across the grating) and somewhat greater than
  this in the orthogonal direction.  These angles are consistent with a raw
  laser diode.  If there were a collimating lens, the beam should be much less
  divergent. (My curiosity finally got the better of me and I ripped the laser
  diode from the barrel to confirm that there was indeed no collimating lens
  hiding inside!)

* Polarizing dichroic beam splitter mirror.  This thick mirror is mounted at
  a 45 degree angle and glued in place.  The outgoing beam is reflected by
  the mirror toward the turning mirror and/or objective lens.

The outgoing beam reflects off of the turning mirror and then passes through
the objective lens:

* Turning mirror (models with horizontally oriented optics only).  This is
  implemented as a coated glass front surface mirror glued to a 45 degree
  angled support which is in turn glued to the casting.  The coating is
  mostly transparent to visible wavelengths of light - it is not aluminized.

* Lens assembly.  This appears to be very similar for all models.  Of course,
  there are probably variations in focal length and other optical properties
  which cannot be determined by inspection.

  - Objective lens uses a double convex plastic molded design glued into a
    plastic frame which mounts the focus and tracking coils and is attached
    to the lens' suspension.  Both surfaces are coated and the top surface, at
    least, is aspheric.  A raised guard ring protects the optical surface from
    damage should the lens come in contact with the spinning disc.

  - Focus actuator is a pair of rectangular formed coils surrounding a pair
    of vertical magnet pole pieces.

  - Focus suspension is a parallelogram molded plastic design.  This assures
    that the lens remains parallel to the disc as it moves up and down.  The
    four hinges appear to be just very thin portions of the molded 4 sided
    box structure.  These hinges are susceptible to weakening or failure.

  - Tracking actuator is a set of 4 circular coils glued to the outside
    surfaces of the focus coils and moving with respect to the same magnetic

  - Tracking suspension is a single vertical molded hinge of similar design to
    that of focus.  A second vertical hinge is also present but is restricted
    from free movement by a resilient rubber material.  This appears to protect
    against sideways shocks.  These hinges are susceptible to failure.

  - The magnets appear to be of a rare-earth type - very strong for their size.

  - A short flex cable links the terminals of the coils to 4 solder pads
    where the flex cable would normally connect from the electronics board.

  - Optical alignment is achieved with a 3-point mounting arrangement for the
    lens assembly.  One of 3 screws with a spring clamps the frame.  The two
    other screws are used for adjustment.  The entire affair is aligned and
    then glued in place at the factory so adjustment in the field is virtually
    impossible - and unneeded in any case.

  - The lens assembly can be removed by unsoldering the 4 solder pad flex
    cable and unscrewing two very small Torx type screws from the top (these
    will succumb to a roughly .7 mm hex wrench.  It then lifts off.  Optical
    alignment should not disturbed.

    Note: Just loosening the Torx screws permits lens assembly to be shifted
    slightly though some small amount of adhesive may need to be removed to
    free it.  This should have an effect on optical alignment.  I will do some
    experiments at some point to determine its precise effect.

After passing back through the objective lens and reflecting off of the turning
mirror, the return beam passes through the dichroic beam splitter mirror and
hits the photodiode array.

* Cylindrical lens.  As far as I can tell there is none.  Viewing an image
  using the entire return optical path (including the objective lens) through
  the photodiode port shows no indication of astigmatic behavior.  There is
  nothing else that can be a cylindrical lens.  Therefore, one must assume
  that the astigmatism present in the laser diode itself is used to advantage
  instead of a separate cylindrical lens.  The effect should be similar.
  Another possibility is that the lens itself IS astigmatic but I could not
  detect it with my primitive (Mark-1 Eyeballs) instrumentation!

* Photodetector array.  Glued to a plate with the 8 pins (7 connected) poking
  out the back and soldered to the flex cable.  Approximate dimensions of
  actual sensor area shown.

                  |<---------- .6 mm ------------>|
             ---- +-------------------------------+
              ^   |       |       |       |       |
              |   |       |       |       |       |
              |   |       |   A   |   B   |       |
              |   |       |       |       |       |
              |   |       |       |       |       |
            .3 mm |   E   |-------+-------|   F   |
              |   |       |       |       |       |
              |   |       |       |       |       |
              |   |       |   C   |   D   |       |
              |   |       |       |       |       |
              v   |       |       |       |       |
             ---- +-------------------------------+

  These are the 6 segment silicon photodiodes (for a three-beam pickup.  (For
  a single-beam pickup, there will be 4 but as far as I know, all Sony pickups
  are all 3 beam types).  Note that the entire active area is a fraction of a
  mm in each dimension.  This emphasizes the likely critical nature of optical
  alignment.  Nonetheless, with everything screwed and/or glued in place, the
  likelihood of this ever changing is small.

* Flexible cables.  In most cases, there are two - a 12 or so conductor cable
  for the laser power and photodiode return signals and a 4 conductor cable
  for the focus and tracking actuator drive.  However, there are many many
  variations on the specific layout.  These are either soldered to the
  electronics board or more commonly, terminate in clamp-type connectors.

  15.14) Interchangeability of Sony KSS pickups

If you have looked inside a variety of CD players, you probably have noticed
(1) that many use Sony pickups (the characteristic octagonal black lens cover)
and (2) that many of *these* appear similar even if their model numbers
differ.  A closer examination will reveal that many many different types use
what would appear to be the identical optical block - the casting that mounts
the lens and its actuators, the laser diode, and photodiode array.  If you
delve even deeper, you would find that the optical paths are identical as
well.  The only obvious difference in many cases are in the mounting and the
way the sled is driven, and in the configuration of the flex cable and its
connections.  So, are the optical blocks themselves indeed interchangeable?

The answer is a definite 'maybe' and servo adjustments may be needed in some
cases (where none would possibly be necessary with an exact replacement).
However, there could be cases where where differences are too great.

I am not sure I believe the differences listed below since much of the pickup
behavior in terms of bump immunity and drop-out performance is based in the
servo loop electronics, not the pickup.  So, while I do not know for sure, my
guess is that the A and B versions would be totally interchangeable if the CD
player electronics have enough adjustment range.

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

Sony KSS150A is compatible with KSS210A and KSS212A.  However, due to signal
levels KSS210A and KSS210B have differing specs.  The rule here is that a
KSS210B can be used in place of a KSS210A, but for optimal performance, an A
should not be used in place of a B.

* B versions designed for "ghetto-blasters" (lower drop-out performance and
  higher vibration resistance).

* A versions for desk-top models (higher drop-out performance, lower vibration

Source of info: Sony Japan Designer who visited me a few years ago.  Yes they
actually send their technical staff around the world to get an idea of what
happens to the products after sale! Not often, but it does happen.  Over the
years I've met designers, technical managers, technicians, and a load of
marketing folks from Japan and Singapore.

  15.15) Super simple optical pickups

Some of the modern generation designs are about as simple as possible and
still perform the needed functions of a single-beam or three-beam optical
pickup.  While the objective lens assembly with its focus and tracking
actuators is of standard construction, there are few additional components.

The CMKS-81X Optical Pickup and Optical Pickup from Philips PCA80SC CDROM are
typical of such designs.  Sony also manufactures such a pickup, apparently
used in some revisions of its PlayStation PSX and elsewhere.

The smallest ones such as the Optical Pickup from the Philips CR-206 CDROM
are only about 1/2" x 5/8" x 3/4" overall - just about the size of the lens

A diagram showing the organization of these simplified three-beam optical
pickups is available in both PDF and GIF format.

* Get CDS3BP: cds3bp.pdf or cds3bp.gif.

This diagram shows the three-beam type.  The only difference for a single-beam
pickup would be to eliminate the difraction grating (and its side beams) and
segments E and F from the photodiode array (or simply not use them).

* The laser diode and photodiode array (LD/PDA) are combined into a single
  package about the size of a larger LD by itself but with 10 pins - 3 for the
  LD and its monitor photodiode and 7 for the PDA (a single-beam pickup such
  as used in Philips/Magnavox products would only need an LD/PDA with 8 pins).

* A glass block or plate roughly 3 mm on a side is glued to the front of this
  LD/PDA package.  In the center is a spot about 1 mm in diameter etched on
  the surface which is the diffraction grating.  This is directly over the
  emitting facet of the LD.  The laser beam passes through this diffraction
  grating on its way out but the return beam is offset to hit the PDA and
  misses the spot entirely.  (A single-beam pickup would not even require this
  diffraction grating!)

* The LD/PDA is pointed at the objective lens (either directly or via a simple
  turning mirror depending on design).

  The pickups in the photos use a turning mirror but this is not needed if
  there is adequate space below deck since the turning mirror's only function
  is to redirect the beam to minimize physical height.

By placing the LD and PDA very close together, the outgoing and return beams
can follow almost the same path forward and in reverse through the optics.
This eliminates all parts associated with separating these beams including the
polarizer, polarizing beam splitter, and quarter wave plate.  There may be a
very slight reduction in signal quality since the optical 'stylus' does not
strike the disc at a precisely perpendicular angle but this is probably very
minimal and more than overcome by the reduction in losses due to the multiple
surfaces and less than perfect performance of the redirection optics.  Thus,
performance is probably better overall, robustness and reliability are
improved, and manufacturing cost is greatly reduced.  Everyone wins!

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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]