Taking Care Of DVD's - Maintenance and Repair

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DVD's are highly resilient but scratches may cause minor data errors but these are easily corrected. Data is stored on DVDs using powerful error correction techniques that can recover from even large scratches with no loss of data. A common misconception is that a scratch will be worse on a DVD than on a CD because of higher storage density and because video is heavily compressed. DVD data density is physically four times that of CD-ROM, so it's true that a scratch will affect more data. But DVD error correction is at least ten times better than CD-ROM error correction and more than makes up for the density increase. It's also important to realize that MPEG-2 and Dolby Digital compression are partly based on removal or reduction of imperceptible information, so decompression doesn't expand the data as much as might be assumed. Major scratches may cause uncorrectable errors that will produce an I/O error on a computer or show up as a momentary glitch in DVD-Video picture. Paradoxically, sometimes the smallest scratches can cause the worst errors because of the particular orientation and refraction of the scratch.

There are many schemes for concealing errors in MPEG video, which may be used in future players. Since DVDs are read by a laser, they are resistant to fingerprints, dust, smudges, and scratches. However, surface contaminants and scratches can cause data errors. On a video player, the effect of data errors ranges from minor video artifacts to frame skipping to complete unplayability. So it's a good idea to take care of your discs. In general treat them the same way as you would a CD ( If my sister is reading this please ignore that last bit of advice ) Your player can't be harmed by a scratched or dirty disc unless globs of nasty substances on it actually hit the lens. Still, it's best to keep your discs clean, which will also keep the inside of your player clean. Don't attempt to play a cracked disc, as it could shatter and damage the player. It doesn't hurt to leave the disc in the player, even if it's paused and still spinning, but leaving it running unattended for days on end might not be a good idea. In general, there's no need to clean the lens on your player, since the air moved by the rotating disc keeps it clean. I

If you use a lens cleaning disc in your CD player, you may want to do the same with your DVD player. ( I use an Allsop DVD lens cleaner which contains no liquids ) It's advisable to use a cleaning disc specifically designed for DVD players, because there are minor differences in lens positioning between DVD and CD players. Periodic alignment of the pickup head is not necessary. Sometimes the laser can drift out of alignment, especially after rough handling of the player, but this is not a regular maintenance item.

Handle only at the hub or outer edge of your DVD disc. Don't touch the shiny surface with your popcorn-greasy fingers.
Store in a protective case when not in use. Don't bend the disc when taking it out of the case, and be careful not to scratch the disc when placing it in the case or in the player tray. Make certain the disc is properly seated in the player tray before you close it.

Keep discs away from radiators, heaters, hot equipment surfaces, direct sunlight (near a window or in a car during hot weather), pets, small children, and other destructive forces ( especially small children as discs can theoretically survive doomsday but not small children) The DVD specification recommends that discs be stored at a temperature between -20 to 50 °C (-4 to 122 °F) with less than 15 °C (27 °F) variation per hour, at relative humidity of 5 to 90 percent. Artificial light and indirect sunlight have no effect on replicated DVDs since they are are made of polycarbonate, polymer adhesives, and metal (usually aluminum or gold), none of which are significantly affected by exposure to light. Exposure to bright sunlight may affect recordable DVDs, specifically write-once DVDs (DVD-R and DVD+R) that use light-sensitive dyes. Magnetic fields have no effect on DVDs, so it's ok to leave them sitting on your speakers. Coloring the outside edge of a DVD with a green marker (or any other color) makes no difference in video or audio quality. Data is read based on pit interference at 1/4 of the laser wavelength, a distance of less than 165 nanometers. A bit of dye that on average is more than 3 million times farther away is not going to affect anything.

If you notice problems when playing a disc, you may be able to correct them with a simple cleaning. Do not use strong cleaners, abrasives, solvents, or acids. With a soft, lint-free cloth, wipe gently in only a radial direction (a straight line between the hub and the rim). Since the data is arranged circularly on the disc, the micro scratches you create when cleaning the disc (or the nasty gouge you make with the dirt you didn't see on your cleaning cloth) will cross more error correction blocks and be less likely to cause unrecoverable errors. Don't use canned or compressed air, which can be very cold and may thermally stress the disc.

For stubborn dirt or gummy adhesive, use water with mild soap, or isopropyl alcohol. As a last resort, try peanut oil. Let it sit for about a minute before wiping it off. There are commercial products that clean discs and provide some protection from dust, fingerprints, and scratches. CD cleaning products work as well as DVD cleaning products. If you continue to have problems after cleaning the disc, you may need to attempt to repair one or more scratches. Sometimes even hairline scratches can cause errors if they just happen to cover an entire error correction (ECC) block. Examine the disc to find scratches, keeping in mind that the laser reads from the bottom.

There are essentially two methods of repairing scratches: 1) fill or coat the scratch with an optical material; 2) polish down the scratch. There are many commercial products that do one or both of these, or you may wish to do it yourself with polishing compounds or toothpaste. The trick is to polish out the scratch without causing new ones. A mess of small polishing scratches may cause more damage than a big scratch. As with cleaning, polish only in the radial direction. Keep in mind that the data layer on a DVD is only half as deep as on a CD, so a DVD can only be repolished about half as many times.

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