ESD Prevention

Whenever you open a Macintosh or other electrical device, you are exposing its internal components to potential damage from the static electricity that builds up in your body through normal activity. Electrostatic discharge occurs when static electricity is discharged from one conductor (such as your finger) to another conductor (such as a memory chip) of a different potential. Exposing an integrated circuit (IC) to as little as 10 volts of static electricity can damage the IC irreparably—and you wouldn't even know it happened, because humans can't perceive static electricity less than 1500 volts.

Since imperceptible ESD can damage integrated circuits found in computer and communications equipment, you must be particularly careful whenever working on Macintosh hardware. Plastics, utensils, polystyrene products, polyester clothing, and even the ungrounded touch of your hand carry sufficient electrostatic charges to damage electronic components, even if you don't feel a spark. This section provides guidelines for preventing ESD damage and describes how to set up an ESD-safe workstation.

ESD Safety Guidelines

Follow these guidelines to reduce the risk of ESD damage:

• Before working on any device containing a printed circuit, ground yourself and the equipment you are working on to an earth or building ground. Use a grounded conductive workbench mat and a grounding wrist strap, and ground the equipment to the mat.

  NOTE

  Make sure you are not grounded when:

  • You work on plugged-in equipment

  • You discharge a cathode-ray tube

  • You work on an unplugged CRT that has not been discharged

  • You are performing live adjustments

  
  

• Handle all integrated circuits by the body, not by the pins. Also, do not touch the edge connectors, exposed circuitry, or printed circuits on boards or cards. Handle ICs, boards, and cards by the edges, or extract them using an ESD-safe pair of pliers or other (safe) tool.

• Never place components on any metal surface. Metal surfaces can hold a static charge that will damage sensitive electronic parts. Use antistatic, conductive, or foam rubber mats.

• Do not touch anyone who is working on integrated circuits. If you touch someone who is properly grounded, your “zap,” or body charge, might cause some damage. Just to be safe, keep your own body charge away from other technicians.

• Use static-shielding storage bags for boards and integrated circuits. Before you leave your bench to take a board to a storage place, put the board in a static-shielding bag. Leave all Apple replacement modules in their ESD-safe packaging until you need them.

• Don't wear polyester clothing or bring plastic, vinyl, or Styrofoam into the work environment. The electrostatic field that surrounds these nonconductors cannot be totally removed without the use of an ionized air generator.

• If possible, keep the humidity in the service area between 70 and 90 percent, and use an ionized air generator if available. Charge levels are reduced (but not eliminated) in high-humidity environments. Using an ionized air generator helps neutralize the charge surrounding nonconductors. However, this type of device can't provide total protection because the static charges often cause ESD damage before the neutralizing process eliminates the charge.

Workstation Setup

Before you start to work on any task involving circuit boards, you must verify that your workstation is ESD safe—that is, that it has equipment and materials designed to prevent ESD damage.

You need the following equipment to set up an ESD-safe workstation:

• A conductive workbench mat and wire lead. When properly grounded, the workbench mat provides a safe place on which to set sensitive components and equipment.

• A wrist strap with a built-in 1-megohm resistor and wire lead. The wrist strap grounds you so that you can safely touch sensitive components without zapping them.

• An equipment wire lead with alligator clips. This wire lead grounds the equipment so that an electrostatic charge cannot build up; it is especially important when you are working on CRTs, which can build up an electrostatic charge even when they are not plugged in.

• A ground polarity tester. The ground polarity tester verifies proper grounding of power outlets.

Setting Up an ESD-Safe Workstation

We all know that setup can be the least exciting, most tedious part of a job. At the same time, setup is a critical aspect of getting that job done properly, and nowhere is that more important than when dealing with electrical systems. Don't overlook the following safe-setup procedure.

1.	Remove all ESD hazards from the area, including nonconductive materials such as Styrofoam, synthetic clothing, plastics, and vinyl. (These materials can't be grounded and can retain a charge for a surprisingly long time—up to a few days.)
2.	Use a ground polarity tester to verify proper grounding of the power outlet. Just because an outlet has three prongs is no assurance that the electrician properly grounded the outlet. Though ground polarity testers vary slightly in design, they are all very easy to use. To use a tester, simply insert the three prongs of the tester into the three-pronged outlet. Most testers display a light pattern that, when matched to the code on the tester, indicates whether the outlet has proper grounding.
3.	If the outlet is grounded, connect the wire lead of the workbench mat to ground. Connect the end of the wire lead that contains the solderless terminal to ground.
4.	Attach the snap fastener of the wire lead to the snap on the workbench mat. Then, slip the wrist strap onto your wrist, allowing the metal part of the wrist strap to touch your skin. All objects in the service area should be grounded to the same potential. Touching the chassis of a machine will bring you to the same potential as the machine. However, since the act of shifting your weight from one foot to the other can generate static charge, momentary touch grounding is not enough. You need the continuous grounding provided by a grounding wrist strap. NOTE Always use a properly grounded mat and wrist strap. Use touch grounding only as a last resort.
5.	Ground the equipment you are working on. The product should not be plugged into the wall outlet. If you have a wire lead with alligator clips, attach the clip to any metal part of the device you are working on. If you do not have proper grounding in your work environment and you are working on a product that has a three-pronged power cord, you can attach the ground pin to the conductive workbench mat using a wire lead with alligator clips. Put one clip on the snap of the mat and the other on the ground pin. Do this only if your work area does not have proper grounding.

A Note on Working Off-Site

When you work at a customer site, you must take the same precautions to avoid ESD damage. Take time to make the work area ESD safe. Bring a workbench mat and a wrist strap with you. (For travel convenience, you may want to use a mat that folds up.) Be sure everything is properly grounded, and never set parts on the floor.

General Maintenance

A lot of general maintenance falls to end users, so it's always a good idea to remind them that it's in their best interest to give their computers the “spa treatment” to help ensure reliability and good performance. This section presents guidelines and hints to help maintain computer equipment in good working order.

Servicing Products That Use Translucent Plastics

Many Apple products are made with translucent or transparent polycarbonate plastic. This plastic is designed to be both aesthetically pleasing and tough; it should stand up to wear quite well.

While translucent plastics are as durable as those used in other computer equipment, scratches and other kinds of minor cosmetic damage may be more visible because the plastics are translucent, rather than opaque.

When servicing products that use translucent plastics, follow these general guidelines:

• Do not scratch the plastic with sharp items or rub it with abrasive materials.

• Do not drop anything heavy on the product or drop the product on the floor.

Cleaning Computer Equipment

Follow these steps for cleaning computers and displays.

To clean the case:

To clean the screen:

Maintaining the Display

While there are some specific differences in how you treat LCD and CRT displays, there are also some universal guidelines. Follow these basic procedures for maintaining the display:

• Turn off the display or turn down the brightness whenever the display is on but not being used. This will prevent the image on the screen from “burning in” and damaging the screen.

• Use Energy Saver preferences (or the Energy Saver control panel in Mac OS 9) to set the display to go to sleep after a specified period of inactivity. You may use Desktop & Screen Saver preferences or a third-party screen-saver program with CRTs; however, note that LCDs don't work the same way as CRTs, and screen savers do not reduce LCD energy consumption or preserve screen life. Refer to Knowledge Base document 10639, “Screen Savers: Using With Liquid Crystal Displays,” or search the Knowledge Base for “screen saver” for more information.

• Make sure the vents on the computer and display are clear and unobstructed.

• Don't let liquid get on or into the display.

If you are trying to eliminate a persistent image from an LCD screen, refer to Knowledge Base document 88343, “Avoiding image persistence on Apple LCD displays.”

Backing Up Files

Of course no one ever expects to lose data, whether for technical or other reasons. This is precisely why you should make backing up a standard part of any workflow. Backing up files helps you prevent the loss of important documents, applications, and other software.

You can back up your files using a dedicated application, such as Retrospect (www.dantz.com), that automatically archives the contents of your hard disk (or any portion you specify). Alternatively, you can back up important documents every day by copying the files to another disk such as an Iomega Zip disk, a volume on a network, an external hard disk, or a writeable optical disc.

Checking for Viruses

A computer virus is a program, usually hidden within another (seemingly innocuous) program, that produces copies of itself to insert into other programs and often performs malicious actions such as destroying data.

Use an antivirus program regularly to check for and delete viruses on the hard disk, especially if you download files from the Internet or share files with others. Choose an antivirus program that alerts you when an email attachment, shared file, or Internet download is infected.

Check periodically for updates to your antivirus program to ensure that the program scans for the latest known viruses.

Search the Knowledge Base for “antivirus.” You'll find, for example:

• “Mac OS: Antivirus Utilities” (document 4454)

• “Macintosh: Where To Find Virus List” (document 11907)

Optimizing the Hard Disk

As you may know, smaller hard disks have a habit of becoming full, and the operating system deals with this by writing bits and pieces of files wherever it can find free space—so while they are fully written, the files are logically fragmented over the surface of the disk. Because the drive's magnetic head has to move all over the place to read or write fragmented files, performance suffers. Third-party utilities, such as the Speed Disk component of Norton Utilities, cropped up to help optimize disks by rewriting files on contiguous tracks on the disks.

Fortunately, all that has changed in recent years. Multigigabyte drives are common and inexpensive, so the lack of storage space that led to fragmentation rarely occurs. Furthermore, Mac OS X contains intelligent routines that, essentially, constantly optimize the hard disk during normal use.

But if you need to know more, you can read Knowledge Base document 17933, “Defragmenting your Mac's hard disk” (for Mac OS 9), or Knowledge Base document 25668, “About disk optimization with Mac OS X.”

Proper Battery Disposal

Whenever you replace a battery—whether it be one from inside a Macintosh computer or a common flashlight—it is important that you dispose of old batteries appropriately. Always dispose of used batteries according to local hazardous waste ordinances. For current instructions, search for “battery disposal” in the Knowledge Base.