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1 Fast Facts: Core Hardware Service Tech... > Preventive Maintenance, Safety, and ...

3.0. Preventive Maintenance, Safety, and Environmental Issues

The 3.0 domain requires knowledge of safety and preventive maintenance. With regard to safety, this domain covers the potential hazards to personnel and equipment when working with high-voltage equipment and items that require special disposal procedures to comply with environmental guidelines. With regard to preventive maintenance, this domain covers knowledge of preventive maintenance products, procedures, environmental hazards, and precautions you should take when working on computer systems. The main points follow:

  • Outer-surface cleaning can be accomplished with a simple soap-and-water solution, followed by a clear water rinse.

  • A damp cloth is the best general-purpose cleaning tool for use with computer equipment.

  • Socket-mounted devices should be reseated (that is, removed and reinstalled to establish a new electrical connection) as part of an anticorrosion effort. Doing this overcomes the chip-creep effect that thermal cycling has on socket-mounted devices.

  • Computer equipment is susceptible to failures caused by dust buildup, rough handling, and extremes in temperature.

  • Missing expansion slot covers adversely affect a system in two ways. First, a missing cover permits dust to accumulate in the system, forming an insulating blanket that causes components to overheat. Second, the heat problem is complicated further by the fact that the missing slot cover interrupts the designed airflow patterns inside the case, causing components to overheat due to lack of or inadequate airflow.

  • If you use a vacuum for cleaning computer systems, you should use a static-free vacuum because normal vacuums are, by nature, static generators. A static-free vacuum has special grounding to remove the static buildup it generates. You should not use a normal vacuum to clean toner from a laser printer.

  • You should check for sources of heat buildup around a computer and its peripherals, including direct sunlight from an outside window.

  • Copies of the system backup should be stored in a convenient but secure place. In the case of secure system backups, such as those for client/server networks, backup copies should be stored where the network administrators can access them but others cannot (for example, in a locked file cabinet). Left unsecured, these copies could be used by someone without authority to gain access to the system or to its data.

  • A keyboard's electronic circuitry is open to the atmosphere and should be vacuumed when you are cleaning around your computer area. Dust buildup on the keyboard circuitry can cause its ICs to fail due to overheating.

  • A mouse's trackball should be removed and cleaned periodically. You should use a lint-free swab to clean the X and Y trackball rollers inside the mouse.

  • Typical power supply variations fall into two categories: transients and sags. Transients are overvoltage conditions, and sags are undervoltage conditions. Transients can be classified as spikes (measured in nanoseconds) or as surges (measured in milliseconds). Sags can include voltage sags (which typically last only a few milliseconds) and brownouts (which can last for a protracted period of time).

  • Inexpensive power line filters called surge suppressers are good for cleaning up dirty commercial power.

  • In the case of a complete shutdown or a significant sag, the best protection against losing programs and data is a UPS.

  • A battery-based UPS cannot keep a system running infinitely. For this reason, you should not connect nonessential, power-hungry peripheral devices such as laser printers to a UPS supply.

  • Monitors, printers, scanners, and other peripheral devices should be stored in their original boxes, using their original packing foam and protective storage bags.

  • Extremely high voltage levels (in excess of 25,000 volts) may be present inside the CRT housing, even up to a year after electrical power has been removed from the unit.

  • In repair situations, the high voltage charge associated with video displays must be discharged. This is accomplished by creating a path from the tube's high-voltage anode to the chassis. With the monitor unplugged from the commercial power outlet, you clip one end of an insulated jumper wire to the chassis ground of the frame, and you clip the other end to a long, flat-blade screwdriver that has a well-insulated handle.

  • In laser printers, the laser light is a hazard to eyesight, the fuser assembly is a burn hazard, and the power supply is a shock hazard.

  • A potential burn hazard is the printhead mechanism of a dot-matrix printer.

  • A Class C fire extinguisher should be present in the work area. Class C extinguishers are the type specified for use around electrical equipment.

  • Laser printer toner cartridges can be refilled and recycled.

  • For both batteries and printer cartridges, the desired method of disposal is recycling.

  • ESD is the most severe form of EMI. The human body can build up static charges that range up to 25,000 volts. These buildups can discharge very rapidly into an electrically grounded body or device. A 25,000-volt surge can be damaging to any electronic device.

  • The ability of the voltage associated with a video monitor to push current through the human body is significant (several amps), but the same ability associated with static is very low (micro-amps—that is, thousandths of an amp). Therefore, it is possible for a lower-voltage device with a higher current rating (such as a 110-volt AC power supply) to be much more dangerous than a higher-voltage source that has a lower current-producing capability (such as static).

  • Some repair shops do not permit compressed air to be used for blowing dust out of keyboards and other computer equipment because it has erroneously been linked to creating ESD.

  • ESD is most likely to occur during periods of low humidity. If the relative humidity is below 50%, static charges can accumulate easily. ESD generally does not occur when the humidity is above 50%. Normal air-conditioning works by removing moisture from the atmosphere, creating low-humidity conditions. Therefore, humidifiers are often used to correct this condition.

  • You should never wear antistatic wrist or ankle straps while working on high-voltage components, such as monitors and power-supply units.

  • Normal operating vibrations and temperature cycling can degrade the electrical connections between ICs and sockets over time. This gradual deterioration of electrical contact between chips and sockets is referred to as chip creep.

  • Good grounding routes the induced EMI signals away from logic circuitry and toward ground potential, preventing the signals from disrupting normal operations. Unlike ESD effects, which are destructive, EMI effects can be corrected without damage.

  • Because a computer system is connected to an actual earth ground, it should always be turned off and disconnected (along with its peripherals) from the power outlet during electrical storms.

  • Technicians normally use antistatic grounding straps that may be placed around the wrist or ankle to ground them to the system they're working on. These straps release any static present on the technician's body and pass it harmlessly to ground potential.

  • Antistatic straps should never be worn while working on higher-voltage components, such as monitors and power-supply units. Some technicians wrap a copper wire around their wrist or ankle and connect it to the ground side of an outlet. This practice is not safe because the resistive feature of a true wrist strap is missing.

  • Most technicians' work areas include antistatic mats as an alternative to wrist or ankle straps; these mats are made out of rubber or other antistatic materials that the technicians stand on while working on the equipment. These mats are particularly helpful in carpeted work areas because carpeting can be a major source of ESD buildup. Some antistatic mats have ground connections that should be connected to the safety ground of an AC power outlet.


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