Disc Repair 101

To understand how digital discs can be repaired, it helps to first know how they're made and what kinds of damages are repairable.

Here are the basics on what you should know about your music CDs, computer CDs, DVDs and game discs.

How CDs are Made

Polycarbonate Plastic Disc

First, data is stamped on the top side of a plastic disc creating millions of ons and offs or zeros and ones. On recordable CDs, data can be burned in at different levels within the plastic disc, for multi-session recording.

Reflective Foil Layer*

Second, a micro thin layer of aluminum (copper, silver or gold on higher quality CDs) is applied to the top of the CD covering the data. This layer reflects light back through the plastic disc, allowing the stamped data to be read.

Lacquer Layer*

Third, lacquer is dripped onto the disc and spun at a high speed to create a thin layer of sealant for the foil layer. This seals in the foil layer, but offers little or no protection for the foil or the data beneath.

Graphic Layer*

Finally, a layer of ink is screened onto the lacquer layer for dynamic graphic and/or sales impact.

*The reflective foil, lacquer, and graphic layers combined are only as thin as a human hair and offer little to no protection of the data beneath them.

If you scratch the bottom, get it repaired! If you scratch the top, you might as well throw it away!

CD Scratches: How CDs are Read

Although there are many different types of optical discs, they all function on the same general principle. The music, picture and/or computer data they store is in digital form. This means it is comprised of millions of ons and offs or zeros and ones – thus the term “digital”.

Digital information is “read” from discs by an infrared laser which projects through the clear protective plastic of a disc bottom, and is either reflected or not reflected back to the laser reader. The encoded surface is made up of microscopic pits and lands which create the ons and offs. By reading the reflected light beams, a disc drive decodes the information on a disc.

A scratch deflects the laser beam off track and information is never received by the laser reader. The smallest of scratches can effect many lines of data.* The most unprotected side of a CD is the top or graphic side!

A laser beam is sent through the bottom of a disc and reads the data stamped on the top side of the plastic disc.

*Most any scratch on the bottom side of the plastic disc can be resurfaced and polished out. A scratch on the top side means lost data. Protect the top with a CD Shield!

Disc Damage: How CDs are Damaged

Scratches are one of the worst enemies of data on an optical disc. Where a scratch occurs determines if your disc is repairable.

Data resides on the top side of the polycarbonate disc. It is extremely important to protect this side of the disc. Manufacturers, however, leave this side highly exposed. A scratch on the top, through the foil or the stamped data, will result in lost data and a nonrepairable disc.

A scratch that occurs on the bottom side of a disc, however, may be resurfaced and polished out. The depth of the scratch will determine the success of the repair. Keep an eye on these scratches during normal use and get them repaired.*

By holding your disc 24” away from a 40 watt light bulb, label side facing the bulb, you can determine which side is scratched. If you see light coming through, pin holes or scratches, this disc is scratched on the label side and is nonrepairable in that area! This disc is lost forever.

The total number of times a disc can be repaired is determined by how deep the scratches are each time you resurface and polish the disc.

How CDs are Repaired

The process uses a pad and polish combination that slowly but continuously removes layer after layer of plastic from the disc. The deeper the scratch, the longer the machine will take to go through the scratch - an average disc takes 3 - 5 minutes.

The most expensive factor in the cost of CD repair is not the machine or the consumables but the labor charge. By eliminating the need to dedicate an employee to CD repair machines like the OneStep help libraries to protect their media while freeing up resources.

Courtesy of Compact Disc Repairman, Inc. www.fixadisc.com