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tools might also come in handy. One of the big issues when working with a PC occurs if you find yourself pulling out parts from the PC and setting them aside. The moment you take a piece out of the PC, it no longer has contact with the systems and may pick up static from other sources. Techs use anti-static mats to eliminate this risk. An anti-static mat acts as a point of common potential; it’s very common to purchase a combination anti-static wrist strap and mat that all connect to keep you, the PC, and any loose components at the same electrical potential (Figure 2-7).

Anti-static wrist straps and mats use tiny resistors—devices that stop or resist the flow of electricity—to prevent anti-static charge from racing through the device. These resistors can fail over time, so it’s always a good idea to read the documentation that comes with your anti-static tools to see how to test those small resistors properly.

Figure 2-7 Anti-static wrist strap and mat combination

Any electrical component not in a PC needs to be stored in an anti-static bag, a specially designed bag that sheds whatever static electricity you have when you touch it, thus preventing any damage to components stored within (Figure 2-8). Almost all PC components come in an anti-static bag when purchased. Experienced techs never throw these bags away, as you never know when you’ll want to pull a part out and place it on a shelf for a while.

Figure 2-8 Anti-static bag

EXAM TIP Always put components in an anti-static bag, not on the bag.

Although having an anti-static wrist strap with you at all times would be ideal, the reality is that from time to time you’ll find yourself in a situation where you lack the proper anti-static tools. This shouldn’t keep you from working on the PC—if you’re careful! Before working on a PC in such a situation, take a moment to touch the power supply every once in a while as you work—I’ll show you where it is in Chapter 3, “The Visible PC”—to keep yourself at the same electrical potential as the PC. Although this isn’t as good as a wrist strap, it’s better than nothing at all.

The last issue when it comes to preventing ESD is that never-ending question—should you work with the PC plugged in or unplugged? The answer is simple: Do you really want to be physically connected to a PC that is plugged into an electrical outlet? Granted, the chances of electrocution are slim, but why take the risk?

* * *

EXAM TIP Always unplug a PC when working inside it.

Electromagnetic Interference (EMI)

A magnetic field interfering with electronics is electromagnetic interference (EMI). EMI isn’t nearly as dangerous as ESD, but it can cause permanent damage to some components and erase data on some storage devices. You can prevent EMI by keeping magnets away from computer equipment. Certain components are particularly susceptible to EMI. Never get a magnet close to:

Floppy disks

Hard drives

Flash drives

CRT (tube) monitors

The biggest problem with EMI is that we often use magnets without even knowing we are doing so. Any device with an electrical motor has a magnet. Many telephones have magnets. Power bricks for laptops and speakers also have magnets. Keep them away!

Radio Frequency Interference (RFI)

Do you ever hear strange noises on your speakers even though you aren’t playing any sounds? Do you ever get strange noises on your cell phone? If so, you’ve probably run into radio frequency interference (RFI). Many devices emit radio waves:

Cell phones

Wireless network cards

Cordless phones

Baby monitors

Microwave ovens

In general, the radio waves that these devices emit are very weak, and almost all electronic devices are shielded to prevent RFI. A few devices, speakers in particular, are susceptible to RFI. RFI will never cause any damage, but it can be incredibly irritating. The best way to prevent RFI is to keep radio-emitting devices as far away as possible from other electronics.

RFI becomes a big problem when two devices share the same frequencies. Cordless phones, baby monitors, and