The books listed in the section: "Suggested references" include additional information on the theory and implementation of digital audio, laserdisc, and optical drive technology.
A Fundamental Introduction to the Compact Disc Player is a somewhat more theoretical discussion of compact disc audio technology with diagrams and even some equations. If it doesn't put you to sleep, you will find quite a bit of interesting information in this article. In either case, it may prove of value. Andy Poggio's relatively short article: From Plastic Pits to "Fantasia" provides a nice overview of CD technology. A site with CD-R specific information including some repair tips is:
Proper care of a CD player does not require much. Following the recommendations below will assure peak performance and long life, and minimize repairs. * Locate the CD player in a cool location. While the CD player is not a significant heat producer, keeping it cool will reduce wear and tear on the internal components and assure a long trouble free life. * Don't locate CD players in dusty locations or areas of high (tobacco) smoke or cooking grease vapors. I cannot force you to quit smoking, but it is amazing how much disgusting difficult to remove brown grime is deposited on sensitive electronic equipment in short order from this habit. * Make sure all audio connections are tight and secure to minimize intermittent or noisy sound. * Finally, store CDs away from heat. The polycarbonate plastic used to mold CDs is quite sturdy but high temperatures will eventually take their toll. Return them to their jewel cases or other protective container when not being played.
You no doubt have heard that a CD should be cleaned and checked periodically. "Purchase our extended warranty" says the salesperson "because CD players are very delicate and require periodic alignment". For the most part, this is nonsense. CD players, despite the astonishing precision of the optical pickup are remarkably robust. Optical alignment is virtually never needed for a component CD player and is rarely required even for portable or automotive units. In fact, modern CD players often don't even have any of these adjustments - the components of the optical pickup are aligned at the factory and then fixed in place with hardening sealer. An occasional internal inspection and cleaning is not a bad idea but not nearly as important as for a VCR. Realistically, you are not going to do any of this anyway. So, sit back and enjoy the music but be aware of the types of symptoms that would be indications of the need for cleaning or other preventive or corrective maintenance - erratic loading, need to convince the CD player to cooperate and play a disc, audio noise, skipping, sticking, and taking longer than usual to recognize a disc or complete a search. If you follow the instructions in the section: "General inspection, cleaning, and lubrication", there is minimal risk to the CD player. However, don't go overboard. If any belts are in good condition (by appearance and stretch test), just clean them or leave them alone. Except for the Sony drawer loading mechanism, belts are rarely as much of a problem in CD players as in VCRs. Of course, acute symptoms like refusal to play or open the door is a sign of the need for emergency treatment. This still may mean that a thorough cleaning is all that is needed.
Every CD, stereo equipment, department, discount, store - and even sidewalk venders - carries CD lens cleaning discs. Are they of any value? Can they cause damage? I generally don't consider CD lens cleaning discs to be of much value for preventive maintenance since they may just move the crud around. However, for pure non-greasy dust (no tobacco smoke and no cooking grease), they probably do not hurt and may do a good enough job to put off a proper cleaning for a while longer. However, since there are absolutely no sorts of standards for these things, it is possible for a really poorly designed cleaning disc to damage the lens. In addition, if it doesn't look like a CD to the optical pickup or disc-in sensor, the lens cleaning disc may not even spin. So, the drawer closes, the drawer opens, and NOTHING has been accomplished!
Although CDs are considerably more tolerant of abuse than LPs, some precautions are still needed to assure long life. Also, despite the fact that only one side is played, serious damage to either side can cause problems during play or render the CD totally useless. It is important that the label side be protected from major scratches which could penetrate to the information layer. Even with the sophisticated error correction used on the CD, damage to this layer, especially if it runs parallel to the tracks, can make the CD unusable. The CD is read by focusing a laser beam through the bottom 1.2 mm of polycarbonate. As a result of the design of the optical system used in the pickup, at the bottom surface, the beam diameter is about 1 mm and thus small scratches appear out of focus and in many cases are ignored and do not cause problems. At the information layer with the pits, the beam diameter has been reduced to under 2 um. Still, scratches running parallel to the tracks are more problematic and can cause the optical pickup to get stuck repeating a track, jumping forward or back a few seconds, or creating noise or other problems on readout. In severe cases, the CD may be unusable especially if the damage is in the directory area. This is why the recommended procedure for cleaning a CD is to use soap and water (no harsh solvents which may damage the polycarbonate or resin overcoat) and clean in a radial direction (center to edge, NOT in the direction of the tracks as you would with an LP). While on the subject of CD care, CDs should always be returned to their original container for storage and not left out on the counter where they may be scratched. If there is a need to put one down for a moment, the label side is probably to be preferred since minor scratches have no effect on performance so long as they do not penetrate to the storage layer below (in which case the CD is probably history). Protectors are available to prevent damage to the label side of the disc. Personally, I think this is taking care to an excessive level but, hey, if you use your CDs as frisbies, go for it!
You do not need a fancy CD cleaning machine. Use a soft cloth, tissue, or paper towel moistened with water and mild detergent if needed. Wipe from center to edge - NOT in a circular motion as recommended for an LP. NEVER use any strong solvents. Even stubborn spots will eventually yield to your persistence. Washing under running water is fine as well. Gently dry with a lint free cloth. Do not rub or use a dry cloth to clean as any dirt particles will result in scratches. Polycarbonate is tough but don't expect it to survive everything. Very fine scratches are not usually a problem, but why press your luck?
Something that not everyone is aware of is the multilevel error handling technology in a CD player. Therefore, a dirty CD may not produce instantly obvious audio problems but can nonetheless result in less than optimal audio performance. Very severe errors - long bursts - will result in audible degradation including noise and/or muting of the sound. Even this may not always be detectable depending on musical context. Shorter runs of errors will result in the player interpolating between what it thinks are good samples. This isn't perfect but will probably not be detected upon casual listening. Errors within the correcting capability of the CIRC code will result in perfect reconstruction. Not all players implement all possible error handling strategies. Therefore, it is quite possible for CD cleaning to result in better sound. However, a CD that is obviously clean will not benefit and excessive cleaning or improper cleaning will introduce fine (or not so fine) scratches which can eventually cause problems.
So the droid in the CD store warned you that dirty CDs could do irepairable harm to your CD player, your stereo, your disposition, etc. "Buy our $19.95 Super-Laseriffic CD cleaning kit". The claim made at one major chain was that dirt or dust on the laser eye would cause heat build-up that would burn out the mechanism. This is different from a dirty disc. The cleaner he was pushing was a little brush attached to a CD that brushed off the lens as it played. This is total rubbish. The power of a CD laser is less than 1 mW and is not concentrated at the lens. And, as noted elsewhere, those cleaning CDs with the little brush are next to useless on anything but the smallest amount of dry dust. There are a lot of suckers out there. Save your money. The worst that can happen is the CD will not play properly. There may be audible noise, it may fail to track properly, abort at random times, or not even be recognized. The electronics will not melt down. It is just about impossible for a dirty CD to do any damage to the player. A dirty lens will only result in disc recognition or play problems similar to those caused by a dirty CD. The laser will not catch fire. The only way damage could occur is if you loaded a cracked CD and the crack caught on the lens. You do not need any fancy CD cleaners in any case - soap or mild detergent and water and a soft cloth are all that are required. If the CD looks clean, it probably will be fine. If there are serious smudges or fingerprints, then cleaning could make a significant difference in performance. For further information, see the sections "CD cleaning" and "General inspection, cleaning, and lubrication".
Unlike old or worn video tapes, it is unlikely that a 'bad' CD could damage your player. If the borrowed CD is dirty, clean it as described in the section: "CD cleaning". If it is badly scratched, the worst that will happen is that it will sound bad - skipping and audible noise. No damage to your player will result. However, if the CD is cracked or broken (this is really difficult to do but I have gotten cracked CDs from public libraries), don't even attempt to load it - a broken edge could catch on the lens and ruin the optical pickup entirely.
The perhaps unexpected answer is a definite *yes* even though everyone has heard about the virtues of non-contact laser playback. There are several ways that a broken or poorly designed or manufactured player can result in scratched discs: * If the lens moves too high while attempting to focus and the mechanical stop does not prevent it from hitting the disc, scratches can occur. On some players, the objective lens can easily go this high if focus is not found on the first pass. Note that in most cases, the lens will not suffer since it is protected by a raised ridge which is what actually scratches the disc. * Mechanical misalignment of the spindle motor or plastic cabinet parts can result in the disc touching the bottom or top of the disc compartment and this can leave scratches. This could be the result of poor or cheap design, shoddy manufacturing, or damage from a fall or other abuse. * If the control logic gets confused, it may allow you to eject a disc while it is still spinning and not fully supported by the spindle platter. A dirty disc that resulted in failure of the CLV servo to lock can result in a disc speed runaway condition with some players. If the drawer is then opened too soon, the disc will still be spinning because the controller has no way of knowing its present status and will not have provided enough reverse torque to stop the spindle motor - or too much and it will be spinning in reverse. The likelihood of any of these is increased with dirty, smudged, warped, or previously damaged discs. Minor scratches may not result in a serious problem and there are products to polish them - don't know how well they work. However, if these scratches can be proven to be a direct consequence of a defective player still under warranty, you should try to get some compensation from the manufacturer for any seriously damaged and now unplayable CDs.
So your five year old decided that your favorite CD would make nice frisbee - didn't really know much about aerodynamics, did he? Now it sounds like a poor excuse for a 78 rpm record. What to do? There seem to be about as many ways of fixing scratches on CDs as producing them in the first place. However, they fall into 3 classes of techniques: 1. Mild abrasives: plastic or furniture polish, Brasso metal polish, toothpaste. These will totally remove minor scratches. 2. Fillers: turtle wax, car wax, furniture wax. Apply over the whole disc and buff out with a lint free cloth. Filling larger scratches should be fairly effective but the disc will be more prone to damage in the future due to the soft wax. 3. Blowtorch. At least one person who claims to have worked for several years in used CD store swears by this technique. Supposedly, he uses a pencil-type pocket butane torch and with great dexterity fuses the surface layer of the readout side of the disc so that all of those scratches and unsightly blemishes-well-melt away. Obviously, there are dangers in using fire on plastic and this is likely a last resort. I would assume that you are rolling with hysterical laughter at this point. In any case, I would not take this approach too seriously :-). As with cleaning a CD, when applying or rubbing any of these materials, wipe from the center to the outside edge. A CD player can generally track across scratches that are perpendicular to its path reasonable well, but not those that run the parallel to the tracks. A mild abrasive will actually remove the scratch entirely if it is minor enough. This is probably more effective where the surface has been scuffed or abraded rather than deeply scratched. Wax-like materials will fill in the space where the scratch is if the abrasive was not successful. Even deep scratches may succumb to this approach. A combination of (1) and (2) may be most effective. Exorbitantly priced versions of these materials are available specifically marketed for repair of CDs. However, the common abrasives and waxes should work about as well. I cannot comment on the use of the blowtorch or how many years of practice is required to get you CD repair license with this technique. However, I am highly skeptical that this works at all and suspect that destruction of the CD is the most likely outcome - totally melting, warping, or cracking or shattering from the thermal stress. In other words, I don't recommend trying the Blowtorch approach unless you have a stack of AOL or MSN CD to sacrifice and you have sufficient accident insurance! An alternative to CD home repair are companies specializing in this service. A couple of these are: Aural Tech CD and CD Repairman. I do not have information as to their effectiveness or cost. However, if you have a very special irreplaceable CD that someone used as a skateboard, one of these may be worth considering.
If scratches penetrate to the information layer, all bets may be off. Much of the optical system compliance with respect to damage depends on the short depth of focus assuring that surface scratches *on the bottom* will be out of focus and ignored. This is not possible with damage to the pits. Even though the CIRC code should be able to deal with thousands of bad bits, such damage can confuse the tracking servos to the point where the disc will be unusable. What if the aluminum (or gold) reflective layer has come off with no damage to the plastic underneath? First of all, I don't know how this could occur unless you were attempting to clean them with a strong solvent. Any physical damage which removed the mirror coating will also damage the pits and recoating will be useless. (Note that I have unintentionally removed the gold coating on a CD-R using a solvent similar to what is in Liquid Wrench(tm). I was actually trying to remove the label but went a little too far! The solvent apparently dissolved the greenish coating or binding underneath allowing the gold film and label to just flake off - very strange behavior. Most of the green layer was still intact. I now have a nice greenish somewhat transparent plastic coaster.) Some discs may still work on some players or drives without the aluminum coating. However, this isn't that likely. How to replace it? Ideally, vacuum deposition is needed. The problem isn't only the reflectance but the micro structure - the original coating was vacuum deposited to conform to the pits and lands of the information layer. It is perfectly uniform below the resolution of the laser beam. Modeling (silver or gold colored) paint is amorphous and rough at these feature sizes and floppy disk write protect stickers or other adhesive backed reflective films don't even come close to contacting the information layer consistently. Mirror paint may work but is a long-shot.
While there are far fewer potential dangers involved in servicing a CD player compared to a TV, monitor, or microwave oven, some minimal precautions are still required when working with the cover removed. These relate to electrical connections to the AC line and exposure to the laser beam: * Electrical: There may be a few exposed electrically live parts from the power line, usually around the power cord entrance, power transformer, and on/off switch. If there are, tape them over or cover them somehow so you need not be concerned with a low tech shock! Unless you are troubleshooting a primary side power supply problem, there will be no need to go near the AC line. * Laser: The laser in a CD player is infra red, near IR - 780 nm - border of visible range but for all intents and purposes invisible. However, it is very low power (generally under 1 mW at the lens) and due to the optics, extremely unlikely that you could be in any danger. Nonetheless, don't go out of your way to look closely into the lens while the unit is on! Caution: there is usually a very low intensity (in appearance) emission from an IR laser which appears deep red. It will be visible as a spot the size of the period at the end of this sentence when the lens is viewed from an oblique angle. This may be a spurious emission in the red part of the spectrum or just your eye's response to the near IR energy of the main beam. In either case, do not be mislead into thinking that the laser is weak as a result of noticing this. The main beam is up to 10,000 times more intense than it appears! Take care. However, the red dot is an indication that the laser is being powered and probably functional, though it is no guarantee of the later. You really need a laser power meter or at least an IR detector to confirm the existence of an IR laser beam. Whenever a full size (5-1/4") CD is in place, there is absolutely no danger of exposure to the laser beam. Reflections of laser light at these power levels are harmless. However, if you are testing with a 3-1/2" 'single' or homemade cut-down test CD (see the section: "Useful ways to mangle CDs"), avoid staring into the lens if there is any chance the laser is powered.
Many problems have simple solutions. Don't immediately assume that your problem is some combination of esoteric complex convoluted failures. For a CD player, it may just be a bad belt or dirty lens. Try to remember that the problems with the most catastrophic impact on operation (a CD player that will not play past track 6) usually have the simplest solutions (the gears that move the optical pickup need lubrication). The kinds of problems that we would like to avoid at all costs are the ones that are intermittent or difficult to reproduce: the occasional audio noise or skipping or a CD player that refuses to play classical CDs (depending on your tastes!) of music composed between the years 1840 and 1910. When attempting to diagnose problems with a CDROM drive, start by trying to get it to play an audio CD. Data readback is more critical since the error correction needs to be perfect. However, with audio playback functional, all of the optical pickup and most of the servo systems and front-end electronics must be working. A CDROM drive which cannot even play a music CD will have no chance of loading Windows 95. If you get stuck, sleep on it. Sometimes, just letting the problem bounce around in your head will lead to a different more successful approach or solution. Don't work when you are really tired - it is both dangerous and mostly non-productive (or possibly destructive). Whenever working on precision equipment, make copious notes and diagrams. You will be eternally grateful when the time comes to reassemble the unit. Most connectors are keyed against incorrect insertion or interchange of cables, but not always. Apparently identical screws may be of differing lengths or have slightly different thread types. Little parts may fit in more than one place or orientation. Etc. Etc. Pill bottles, film canisters, and plastic ice cube trays come in handy for sorting and storing screws and other small parts after disassembly. Select a work area which is well lighted and where dropped parts can be located - not on a deep pile shag rug. Something like a large plastic tray with a slight lip may come in handy as it prevents small parts from rolling off of the work table. The best location will also be relatively dust free and allow you to suspend your troubleshooting to eat or sleep or think without having to pile everything into a cardboard box for storage. Another consideration is ESD - Electro-Static Discharge. The electronic components - especially the laser diode - in CD players, CDROM drives, and similar devices, are vulnerable to ESD. There is no need to go overboard but do take reasonable precautions like not wearing clothing made of wool that tends to generate static. When working on component CD and laserdisc players, get into the habit of touching a ground like the metal chassis before touching any circuit components. The use of an antistatic wrist strap would be further insurance especially if the optical pickup assembly needs to be unplugged for any reason. A basic set of precision hand tools will be all you need to disassemble a CD player and perform most adjustments. However, these do not need to be expensive. Needed tools include a selection of Philips and straight blade screwdrivers, needlenose pliers, wire cutters, tweezers, and dental picks. A jeweler's screwdriver set is a must particularly if you are working on a portable CD player or CDROM drive. For making servo adjustments, non-metallic fine tip jeweler's screwdrivers or alignment tools will be essential as some of the front-end circuitry may be sensitive to body capacitance - contact with the slot may alter the behavior of the player (for better or for worse). In a pinch, wrapping electrical tape around the part of a normal jeweler's that you grasp will probably provide enough isolation. However, with a tool with a blade made out of an insulator, you will be less likely to accidentally short things out as well You should not need any CD specific tools except in the unlikely event you get into optical alignment in which case the service manual will detail what tools and special rigs are needed. A low power fine tip soldering iron and fine rosin core solder will be needed if you should need to disconnect any soldered wires (on purpose or by accident) or replace soldered components. See the document: "Troubleshooting and Repair of Consumer Electronics Equipment" for additional info on soldering and rework techniques. For thermal or warmup problems, a can of 'cold spray' or 'circuit chiller' (they are the same) and a heat gun or blow dryer come in handy to identify components whose characteristics may be drifting with temperature. Using the extension tube of the spray can or making a cardboard nozzle for the heat gun can provide very precise control of which components you are affecting. For info on useful chemicals, adhesives, and lubricants, see "Repair Briefs, an Introduction" as well as other documents available at this site.
Don't start with the electronic test equipment, start with some analytical thinking. Many problems associated with consumer electronic equipment do not require a schematic (though one may be useful). The majority of problems with CD are mechanical and can be dealt with using nothing more than a good set of precision hand tools; some alcohol, degreaser, contact cleaner, light oil and grease; and your powers of observation (and a little experience). Your built in senses and that stuff between your ears represents the most important test equipment you have. A DMM or VOM is necessary for checking of power supply voltages and testing of sensors, LEDs, switches, and other small components. This does not need to be expensive but since you will be depending on its readings, reliability is important. Even a relatively inexpensive DMM from Radio Shack will be fine for most repair work. For servo and other electronic problems, an oscilloscope will be useful. However, it does not need to be fancy. A 10 to 20 MHz dual trace scope with a set of 10X probes will be more than adequate for all but the most esoteric troubleshooting of CD players and CDROM drives. To determine if the laser diode is working properly, a laser power meter is very useful. Such a device is expensive but is often essential to properly and safely adjust laser power on many CD players and CDROM drives. However, for many problems, simply knowing that an IR laser beam is being emitted is enough. For this, the simple device described in the section: "IR detector circuit" is more than adequate. Alternatively, an inexpensive IR detector card or even some camcorders can perform the same function. A stereo amplifier and loudspeakers is essential to allow your most important piece of audio test equipment to function effectively - your ears. A lot can be determined by listening to the audio output to distinguish among dirt, lubrication, servo, control, and other mechanical or electronic problems. I would caution against the use of headphones as a sudden burst of noise could blow your eardrums and spoil your entire day. For testing of optical pickups, some additional equipment will be needed. However, this will be detailed in the section: "Testing of Optical Pickup Assemblies".
An inexpensive test CD is nice to have just to be able to play known frequencies and volume levels. However, it is not essential - any half decent CD will work just fine for most tests. For many players, even an old CDROM disc will be adequate to diagnose startup problems. However, to fully exercise the limits of the player, a disc with a full 74 minutes of music will be needed - Beethoven's Ninth Symphony is a good choice (even if you are not into classical music) since it is usually very close (or sometimes slightly over) this length of time. Keep those old demo CDs or even obsolete CDROM discs - they can be used for testing purposes. Where an optical deck has a servo problem, the disc will end up spinning out of control. Stopping this suddenly may result is the CD scraping itself against the drawer or or base of the deck and getting scratched. Therefore, some 'garbage' discs are always handy for testing purposes. To evaluate tracking and error correction performance, any CD can be turned into a test CD with multiple width strips of black tape, a felt tip marker, or even a hand drill! In fact, some professional test discs are made in exactly this manner. Also see the sections: "Comments on test discs" and "Custom test CDs using CD-Rs".
These suggestions will allow you to put some of those AOL CDs to good use (well, besides making high tech coasters)! * For portable CD players where the designers in their infinite wisdom put some of the servo adjustments *under* the spinning disc, a 3-1/2" CD 'single' is extremely handy. A normal CD can be cut down as well - to whatever size you need as long as enough actual tracks are left so that the directory and a few minutes of music/data remain - this could be as little as about 2-1/2" to gain access to the adjustments on some models. This surgery is best done on a band saw with a narrow fine tooth blade. However, tiny cracks may grow in from the edge (overnight, even) if the disc is subjected to any heating or stress from cutting or smoothing. Perhaps some annealing is needed to prevent these from getting started. Note that the lower mass (actually the lower moment of inertia for you purists) of the small CDs may alter the servo response somewhat. Putting a heavy metal ring or washer on top should help. However, this is still much much better than continually having to remove a normal CD to get at the adjustments, incrementally moving them one way or another, and then replacing the CD to see how you made out. One can grow old doing this! The little CDs will enable you to monitor the test points as the adjustments are made which is also a definite advantage :-). The RCA RP-7903A Portable CD Player is an example of a design where this type of modified CD is invaluable for testing. * A handy special miniature CD can be made to permit viewing of the focusing action on any CD player or CDROM drive as long as you can get to the top of the deck while testing. Using a band saw, cut a garbage disc down so as to leave only a 1-1/2" diameter center hub with a 1/2" by 1/2" tab sticking out from it. This can then be positioned by hand to just cover the lens while it is supposed to be doing its focus search. * An alternative that will permit you to view both the laser output (from a safe distance) and the focusing action is to create a window in a garbage CD by removing the label and aluminum layers from an area of the CD at the inner tracks - at least a square inch worth. Lacquer thinner (nail polish remover, with adequate ventilation) will probably work to remove the label. Fine sand paper or steel wool will remove the aluminum and information pits/lands (grooves). Then polish with a buffing wheel or old rag. Caution: when using any of these cut-down or windowed test CDs, or 3-1/2" 'singles', avoid staring into the lens when the laser is powered. See the section: "SAFETY".
WARNING: you will void the warranty, if any. You may make the problem worse, possibly much worse. If the player partially worked, it may no longer even recognize the disc directory. You may accidentally damage parts that were perfectly fine. If you should decide to then have the unit professionally serviced, you may find that the shop simply refuses to touch it if they suspect your tampering. There is nothing worse than having to undo 'fixes' introduced by a well intentioned do-it-yourselfer where the state of the player is now a total unknown. At best you will be charged for this effort on a time and materials basis. It may be very costly. It may not be worth the expense. A CD player still under warranty should probably be returned for service for any covered problems except those with the most obvious and easy solutions. On the other hand, it is possible that you will do a better job than some repair shops. You will probably have a better understanding of the basic theory and will certainly be able to spend much more time on the problem. And, of course, hobbiest/handyman's time is cheap - as in free. * Component CD players. It is generally very easy to remove the top cover on most CD players. There are usually some very obvious screws on the sides and possibly back as well. These are nearly always Philips head type - use the proper screwdriver. Once all the screws are out, the top cover will lift up or slide back and then come off easily. If it still does not want to budge, recheck for screws you may have missed. Once the top cover is removed, the optical deck and electronics board will usually be readily accessible. In rare cases, removing the bottom cover will provide access to the solder side of the electronics board. However, with most CD players, the bottom is solid sheet metal and the entire board would need to be unmounted. On some, the electronics board is mounted upside-down so there is full access to the wiring side once the cover is removed. * With most single play designs, the entire optical deck can be lifted out after removing 3 or 4 screws. One screw may have a grounding contact under it. Replace this in exactly the same position. There may be fragile flexible cables. Be careful so as not to damage any. Usually, these cables plug in to connectors on the electronics board and permit the entire optical deck to be easily replaced if needed (not very common, however, despite what you may have heard). * For changers, details will depend on the particular model but in general, it is more likely that removal of the entire changer mechanism will be more involved. However, this is usually not needed unless there is an actual mechanical problem with it. With Pioneer cartridge changes, for example, the optical deck is easily removed with just 4 screws. * For portables, the bottom plate or top cover usually comes off after removing several very tiny screws - use the proper size Philips blade jeweler's screwdriver and don't lose them. Then, you either have access to the bottom of the mainboard or the top of the mainboard blocked mostly by the optical deck. With the RCA RP-7903A Portable CD Player, it is the latter and the pickup and/or normal size CD conveniently block all access to servo adjustments and test points (which as is often the case, are ummarked in this RCA unit). These types of CD players are usually quite a pain to troubleshoot! Of course, there are also many components including most of the large multilegged ICs surface mounted on the *bottom* side of the mainboard which makes for even more fun should probing be required! You can easily see all the 'stuff' packed into a box just slightly larger than a CD! * For CDROM drives, both top and bottom covers may be removable depending on model. These are more wide open than portables, especially the newer models where everything has been shrunk to a tiny optical pickup and circuit board with a few large ICs. Unfortunately, adjustments (if any) and test points are even less likely to be labeled on CDROM drives. All testing will also require a working PC unless your model has built-in audio play capability. Make notes of screw location and type and immediately store the screws away in a pill bottle, film canester, or ice cube tray. When reassembling the equipment make sure to route cables and other wiring such that they will not get pinched or snagged and possibly broken, or have their insulation nicked or pierced, and that they will not get caught in moving parts. Replace any cable ties that were cut or removed during disassembly and add additional ones of your own if needed. Some electrical tape may sometimes come in handy to provide insulation insurance as well. (This applies mostly to portables and CDROM drives - component CD players are very wide open.
The process of reading a CD is digital. I have seen and heard advertisements for sonic rings or special magic markers to improve the quality of the digital audio reproduction. This is total bunk. Don't waste your money. These products do nothing beyond depleting your pocketbook - and enhancing those of the vendors. For more amusement, see the section: "Totally worthless gadgets for CD enthusiasts".Go to [Next] segment
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