Rosewill Computer Case 422 Informacje Techniczne Pobierz pdf (Strona 37)

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Chapter 4 • Disassembly and Power

Tech

Tip

Disassembly Overview

It is seldom necessary to completely disassemble a computer. However, when a technician

is first learning about PCs, disassembly can be both informative and fun. Technicians might

disassemble parts of a computer to perform preventive cleaning or to troubleshoot a problem.

It may also be appropriate to disassemble a computer when it has a problem of undetermined

cause. Sometimes, the only way to diagnose a problem is to disassemble the computer out-

side the case or remove components one by one. Disassembling a computer outside the case

may help with grounding problems. A grounding problem occurs when the motherboard

or adapter is not properly installed and a trace (a metal line on the motherboard or adapter)

touches the computer frame, causing the adapter and possibly other components to stop work-

ing. Don’t forget to remove jewelry and use proper lifting techniques, as described in Figure

1.1 (see Chapter 1) before disassembling a computer.

Electrostatic Discharge (ESD)

You must take many precautions when disassembling a computer. The electronic circuits

located on the motherboard and adapters are subject to ESD. ESD (electrostatic discharge) is

a difference of potential between two items that causes static electricity. Static electricity can

damage electronic equipment without the technician’s knowledge. The average person requires

a static discharge of 3,000 volts before he or she feels it. An electronic component can be dam-

aged with as little as 30 volts. Some electronic components may not be damaged the first time

static electricity occurs. However, the effects of static electricity can be cumulative, weakening

or eventually destroying a component. An ESD event is not recoverable—nothing can be done

about the damage it induces. Electronic chips and memory modules are most susceptible to

ESD strikes.

Atmospheric conditions affect static electricity. When humidity is low, the potential for

ESD is greater than at any other time; however, too much humidity is bad for electronics. Keep

humidity between 45 and 55 percent to reduce the threat of ESD.

A technician can prevent ESD by using a variety of methods. The most common tactic is

to use an antistatic wrist strap. One end encircles the technician’s wrist. At the other end,

an alligator clip attaches to the computer. The clip attaches to a grounding post or a metal part

such as the power supply. The electronic symbol for ground follows:

An antistatic wrist strap allows the technician and the computer to be at the same voltage

potential. As long as the technician and the computer or electronic part are at the same poten-

tial, static electricity does not occur. An exercise at the end of the chapter demonstrates how to

attach an antistatic wrist strap and how to perform maintenance on it. Technicians should use

an ESD wrist strap whenever possible.

A resistor inside an antistatic wrist strap protects the technician in case something acci-

dentally touches the ground to which the strap attaches while he or she is working inside a

computer. This resistor cannot protect the technician against the possible voltages inside a

monitor. See Figure 4.1 for an illustration of an antistatic wrist strap. Figure 4.2 shows a good

location for attaching an antistatic wrist strap.

When not to wear an antistatic wrist strap

Technicians should not wear an ESD wrist strap when working inside a CRT monitor because

of the high voltages there.

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