Contents:
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
approach.
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.
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.
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.
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.
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 distributor. * 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 somehow). 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".
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).
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!
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.
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.
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.
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.
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 surface. * 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.Go to [Next] segment
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