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 damaged 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 potential, 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 accidentally 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.
