OBJECTIVES

OBJECTIVESOBJECTIVES

1. Demonstrate proper cleaning procedures for various system components. 2. Describe electrostatic discharge hazards and methods of preventing ESD. 3. List the steps for proper IC handling. 4. Define the term ground. 5. Describe the two types of uninterruptible power supplies (UPS) and state their qualities. 6. State typical precautions that should be observed when working on computer

equipment. 7. Perform generic preventive maintenance routines as required (for example, remove excess toner, defragment hard drives, and create back-up copies). 8. Detail routine preventive maintenance procedures as they apply to hard and floppy disks. 9. Perform basic disk management functions on a hard drive, including using ScanDisk, CHKDSK, and Defrag utilities.10. Use backup software to create backups of important data.11. Use software utilities to identify and remove viruses from computer systems.12. List precautionary steps that should be taken when handling floppy disks.(continued)

OBJECTIVES (CONTINUED)OBJECTIVES (CONTINUED)

13. List steps to clean a dot-matrix, ink-jet, or laser printer.14. Establish and maintain preventive maintenance schedules for users.15. Differentiate between various UPS specifications and state how they apply to a given situation.16. State potential hazards that are present when working with laser printers, monitors, and other equipment.

Liquid cleaning compounds

Identify the purpose of various types of preventive maintenance measures, products and procedures, and when and how to use them. Content may include the following:

Types of materials to clean contacts and connections

Non-static vacuums (chassis, power supplies, fans)

Cleaning monitors

Cleaning removable media devices

Ventilation, dust, and moisture control on the PC hardware interior.

(continued)

Hard disk maintenance (defragging, ScanDisk, CHKDSK)

Identify the purpose of various types of preventive maintenance measures, products and procedures, and when and how to use them. Content may include the following: (continued)

Verifying UPS (Uninterruptible Power Supply) and suppressors

Cleaning is a major part of keeping a Cleaning is a major part of keeping a computer system healthy. Therefore, the computer system healthy. Therefore, the technician’s tool kit should also contain a technician’s tool kit should also contain a collection of cleaning supplies. Along collection of cleaning supplies. Along with hand tools, it will need a lint-free, with hand tools, it will need a lint-free, soft cloth (chamois) for cleaning the soft cloth (chamois) for cleaning the plastic outer surfaces of the system.plastic outer surfaces of the system.

Know the common methods of cleaning various computer components.

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Know what types of materials/techniques can be used to clean different areas of the computer system.

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Figure 8-1: How to Handle a PC Board

The environment around a computer system The environment around a computer system and the manner in which the computer is used and the manner in which the computer is used determine greatly how many problems it will determine greatly how many problems it will have. Occasionally dedicating a few moments of have. Occasionally dedicating a few moments of care to the computer can extend its Mean Time care to the computer can extend its Mean Time Between Failures (MTBF) period considerably. Between Failures (MTBF) period considerably. This activity, involving maintenance not This activity, involving maintenance not normally associated with a breakdown, is called normally associated with a breakdown, is called Preventive Maintenance (PM).Preventive Maintenance (PM).

Know what environmental conditions or activities are most likely to lead to equipment failures.

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Be aware of the effect that missing expansion slot covers have on the operation of the system unit.

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Know that computer vacuums have special grounding to dissipate static buildup that can damage computer devices.

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CHALLENGE #1CHALLENGE #1

When you arrive at a customer’s office to repair one of their key computers, you trace the problem down to a defective microprocessor. The system has apparently been upgraded several times over its lifetime there are several open expansion slots and loose cables inside the system unit. There is also a layer of dust on all the internal components. What should you tell the manager when she asks you about what you have found?

Figure 8-2: Caution Areas Inside the Monitor

Figure 8-3: Proper Packing of a Hard Drive for Shipment

Figure 8-4: Data Backup Systems

Be aware of the precautions that should be employed with storing system backups.

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Unlike hard-disk drives, tape drives, floppy Unlike hard-disk drives, tape drives, floppy drives, and CD-ROM/DVD drives are at least drives, and CD-ROM/DVD drives are at least partially open to the atmosphere, and their partially open to the atmosphere, and their media may be handled on a regular basis. This media may be handled on a regular basis. This opens these drive units up to a number of opens these drive units up to a number of maintenance concerns not found in hard disk maintenance concerns not found in hard disk drives. Also, the removable cartridges, disks, drives. Also, the removable cartridges, disks, or discs can be adversely affected by extremes or discs can be adversely affected by extremes in temperature, exposure to magnetic and in temperature, exposure to magnetic and electromagnetic fields, bending, and airborne electromagnetic fields, bending, and airborne particles that can lead to information loss.particles that can lead to information loss.

Figure 8-5: Cleaning the R/W Heads

Input peripherals generally require very Input peripherals generally require very little in the way of preventive maintenance. little in the way of preventive maintenance. An occasional dusting and cleaning should An occasional dusting and cleaning should be all that’s really required. There are, be all that’s really required. There are, however, a few common-sense items to however, a few common-sense items to keep in mind when using an input device keep in mind when using an input device that should prevent damage to the device, that should prevent damage to the device, and ensure its longevity.and ensure its longevity.

Remember that dust can settle into the keyboard through the cracks between the keys.

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Figure 8-6: Cleaning the Keyboard

Figure 8-7: Cleaning the Rollers in a Mouse

Know how to clean a trackball mouse.

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Because printers tend to be much more Because printers tend to be much more mechanical than other types of computer mechanical than other types of computer peripherals, they require more effort to peripherals, they require more effort to maintain. Printers generate pollutants, such maintain. Printers generate pollutants, such as paper dust and ink droplets, in everyday as paper dust and ink droplets, in everyday operation. These pollutants can build up on operation. These pollutants can build up on mechanical parts and cause them to wear. mechanical parts and cause them to wear. As the parts wear, the performance of the As the parts wear, the performance of the printer diminishes. Therefore, printers printer diminishes. Therefore, printers require periodic cleaning and adjustments require periodic cleaning and adjustments to maintain good performance.to maintain good performance.

WARNINGWARNING

Cleaning the printer and its mechanisms periodically adds to its productivity by removing contaminants that cause wear. Vacuum the inside of the unit, after applying antistatic solution to the vacuum’s hose tip. Wipe the outside with a damp cloth, also using antistatic solution. Brush any contaminant buildup from the printer’s mechanical components, using a soft-bristled brush. Never lubricate the platen assembly of the printer.

Adjust the printhead spacing.11

Check the tension on the printhead positioning belt.

22

Clean the printer and its mechanisms.33

Clean the printer’s roller surfaces.44

Clean the surface of the platen.55

Clean the surface of the dot-matrix printhead.66

The steps to cleaning a dot-matrix printer are described in the following steps:

(continued)

Apply light oil to the gears using a swab.88

Turn the platen to distribute the oil.99

Apply a light coating of oil to the rails.1010

Move the carriage assembly to distribute the oil.

1111

The steps to cleaning a dot-matrix printer are described in the following steps: (continued)

Clean the paper-handling motor’s gear train.77

Adjust the printhead spacing.11

Check the tension on the printhead positioning belt.

22

Clean the printer and its mechanisms.33

Clean the printer’s roller surfaces.44

Clean the surface of the platen.55

Clean the surface of the ink-jet printhead.66

The steps to cleaning an ink-jet printer are provided by the following steps:

(continued)

Apply light oil to the gears using a swab.88

Turn the platen to distribute the oil.99

Apply a light coating of oil to the rails.1010

Move the carriage assembly to distribute the oil.

1111

The steps to cleaning an ink-jet printer are provided by the following steps:


Remember acceptable methods for cleaning laser printers.

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Remove dust build-up, and excess toner, from the interior.

11

Clean the laser printer’s rollers.22


Apply light oil to the gears, using a swab.44

Distribute the oil throughout the gear train.55

Clean the corona wires.66

Steps to cleaning a laser printer are described in the following hands-on activity:

Direct sunlight from an outside window

Locations of portable heaters in the winter

Papers/books piled up around the equipment

Check for other sources of heat buildup around the computer and its peripherals. These sources include:

Verifying UPS (uninterruptible power supply) and suppressors

Identify various types of preventive maintenance measures, products, and procedures and when and how to use them. Content may include the following:

Avoid power variations Avoid power variations Digital systems Digital systems tend to be sensitive to power variations tend to be sensitive to power variations and losses. Even a very short loss of and losses. Even a very short loss of electrical power can shut a digital electrical power can shut a digital computer down, resulting in a loss of any computer down, resulting in a loss of any current information that has not been current information that has not been saved to a mass storage device.saved to a mass storage device.

Transients — an over-voltage condition, while sags are an under-voltage condition. Over-voltage conditions can be classified as spikes (measured in nanoseconds), or as surges (measured in milliseconds).

Typical power supply variations fall into two categories:

Sags — can include voltage sags and brownouts. A voltage sag typically lasts only a few milliseconds, while a brownout can last for a protracted period of time.

Be aware of how undervoltage and overvoltage situations are categorized (i.e., time lengths).

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Clamping speed

Clamping voltage

There are two factors to consider when choosing a surge suppresser:

Know what type of devices will protect systems from minor power sags and power surges.

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Know what type of device prevents power interruptions that can corrupt data.

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Uninterruptible power supplies are Uninterruptible power supplies are battery-based systems that monitor battery-based systems that monitor the incoming power and kick in the incoming power and kick in when unacceptable variations occur when unacceptable variations occur in the power source. The term UPS in the power source. The term UPS is frequently used to describe two is frequently used to describe two different types of power backup different types of power backup systems.systems.

Figure 8-8: UPS System

Figure 8-10: Connecting the UPS in the System

High-power-consumption peripheral devices, such as laser printers, should not be connected directly to the UPS. These devices can overload the UPS and cause data loss.

NOTENOTE

The On/Off switch

The commercial AC power supply

The UPS input circuit breaker

The UPS battery connector

If the UPS system does not come on, there are several items that should be checked. These items include:

Remember that nonessential peripheral devices should not be connected to UPS supplies.

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Of course, you should be aware that any UPS testing should be performed while the computer is not in active use and when there is no chance of data loss due to unexpected test results.

NOTENOTE

Be aware that the UPS system will not be able to control the operation of the computer without the serial communications cable installed.

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Know that the best device for transporting computer equipment is the original manufacturer’s packaging, including the antistatic foam and bags used to pack it.

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Situations that could present a danger or hazard

Identify various safety measures and procedures, and when/how to use them. Content may include the following:

Potential hazards and proper safety procedures relating to:

High-voltage equipment

Power supply

CRTs

In most IBM compatibles, there are only In most IBM compatibles, there are only two potentially dangerous areas. One of two potentially dangerous areas. One of these is inside the CRT display, and the these is inside the CRT display, and the other is inside the power supply unit. Both other is inside the power supply unit. Both of these areas contain electrical voltage of these areas contain electrical voltage levels that are lethal. However, both of levels that are lethal. However, both of these areas reside in self-contained units, these areas reside in self-contained units, and you will usually not be required to and you will usually not be required to open either unit.open either unit.

Be aware of the voltage levels that are present inside a CRT cabinet.

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Laser printers contain many hazardous Laser printers contain many hazardous areas. The laser light can be very areas. The laser light can be very damaging to the human eye. In addition, damaging to the human eye. In addition, there are multiple high-voltage areas in there are multiple high-voltage areas in the typical laser printer, and a high-the typical laser printer, and a high-temperature area to contend with as well.temperature area to contend with as well.

Know the areas of the computer system that are dangerous for personnel and how to prevent injury from these areas.

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Remember the type of fire extinguisher that must be used with electrical systems, such as a PC.

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Special disposal procedures that comply with environmental guidelines

Identify environmental protection measures and procedures, and when/how to use them. Content may include the following:

Batteries

CRTs

Chemical solvents and cans

MSDS (Material Safety Data Sheet)

Most computer components contain some Most computer components contain some level of hazardous substances. Printed level of hazardous substances. Printed circuit boards consist of plastics, precious circuit boards consist of plastics, precious metals, fiberglass, arsenic, silicon, gallium, metals, fiberglass, arsenic, silicon, gallium, and lead. CRTs contain glass, metal, and lead. CRTs contain glass, metal, plastics, lead, barium, and rare earth plastics, lead, barium, and rare earth metals. Batteries from portable systems metals. Batteries from portable systems can contain lead, cadmium, lithium, can contain lead, cadmium, lithium, alkaline manganese, and mercury.alkaline manganese, and mercury.

Remember that toner cartridges from a laser printer should be recycled.

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Remember that the proper disposal method for batteries is to recycle them.

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What the material is

Its hazardous ingredients

Its physical properties

Fire and explosion data

Reactivity data

Spill or leak procedures

Health hazard information

Any special protection information

Any special precaution information

The MSDS contains information about:

ESD (Electrostatic Discharge) precautions and procedures

Identify various safety measures and procedures, and when/how to use them. Content may include the following:

What ESD can do, how it may be apparent or hidden

Common ESD protection devices

What is ESD What is ESD Electrostatic Discharges Electrostatic Discharges (ESD) are the most severe form of (ESD) are the most severe form of Electromagnet Interference (EMI). The Electromagnet Interference (EMI). The human body can build up static charges that human body can build up static charges that range up to 25,000 volts. These buildups can range up to 25,000 volts. These buildups can discharge very rapidly into a electrically discharge very rapidly into a electrically grounded body, or device. Placing a 25,000-grounded body, or device. Placing a 25,000-volt surge through any electronic device is volt surge through any electronic device is potentially damaging to it.potentially damaging to it.

Remember what the acronym ESD stands for.

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Moving people

Improper grounding

Unshielded cables

Poor connections

Moving machines

Low humidity (hot and dry conditions)

The most common causes of ESD are:

Memorize the conditions that make ESD more likely to occur.

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Be aware that compressed air can be used to blow dust out of components and that it does not create ESD.

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Memorize conditions and actions that produce electrostatic discharge.

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You may be a little confused by the fact that we You may be a little confused by the fact that we warn you about the lethal 25,000 volts present inside warn you about the lethal 25,000 volts present inside the monitor and then say that the 10,000 to 25,000 the monitor and then say that the 10,000 to 25,000 volts of ESD is not harmful to humans. The reason volts of ESD is not harmful to humans. The reason for this is the difference in current-delivering for this is the difference in current-delivering capabilities created by the voltage. For example, the capabilities created by the voltage. For example, the circuitry in the monitor and the power supply is circuitry in the monitor and the power supply is capable of delivering amps of current, while the capable of delivering amps of current, while the current-producing capability of the electrostatic current-producing capability of the electrostatic charge is less than a thousandth of that. Therefore, charge is less than a thousandth of that. Therefore, the 120 Vac, 1-amp current produced by the power the 120 Vac, 1-amp current produced by the power supply unit is lethal, while the 25,000 Vdc, supply unit is lethal, while the 25,000 Vdc, microamps of current produced by ESD is not.microamps of current produced by ESD is not.

Remember that the current capabilities of electrical devices establish the potential danger levels associated with working around them.

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You have been asked to consult on the design of your company’s new repair facility near Phoenix, Arizona. In particular, management wants to know how to equip the work areas of their new facility. You have not been to the site, but you know that it is in a hot desert environment. Also, the building will be air-conditioned. How should you advise them about precautions that should be taken with the work area?

Figure 8-10: Typical Antistatic Devices

Know when not to wear an antistatic wrist strap.

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Before touching any components inside the system, touch an exposed part of the chassis or the power supply housing with your finger. Grounding yourself in this manner will ensure that any static charge present on your body is removed. This technique should be used before handling a circuit board or component. Of course, you should be aware that this technique will only work safely if the power cord is attached to a grounded power outlet. The ground plug on a standard power cable is the best tool for overcoming ESD problems.

To avoid damaging static-sensitive devices, the following procedures will help to minimize the chances of destructive static discharges:

(continued)

Figure 13-8: Discharging Through the Power Supply Unit

Do not remove ICs from their protective tubes (or foam packages) until you are ready to use them. If you remove a circuit board or component that contains static-sensitive devices from the system, place it on a conductive surface, such as a sheet of aluminum foil.

To avoid damaging static-sensitive devices, the following procedures will help to minimize the chances of destructive static discharges: (continued)

(continued)

In the event that you have to replace a hard-soldered IC, you may want to install an IC socket along with the chip. Be aware that 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. It is a good practice to reseat any socket-mounted devices when handling a printed circuit board. Before removing the IC from its protective container, touch the container to the power supply of the unit in which it is to be inserted.


(continued)

Be aware of the effects that temperature cycling can have on socket-mounted devices.

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Use antistatic sprays or solutions on floors, carpets, desks, and computer equipment. An antistatic spray or solution, applied with a soft cloth, is an effective deterrent to static.


(continued)

Install static-free carpeting in the work area. You can also install an antistatic floor mat as well. Install a conductive tabletop to carry away static from the work area. Use antistatic tablemats.

Use a room humidifier to keep the humidity level above 50% in the work area.


The term ground is often a source of The term ground is often a source of confusion for the novice, because it confusion for the novice, because it actually encompasses a collection of actually encompasses a collection of terms. Generically, ground is simply any terms. Generically, ground is simply any point from which electrical point from which electrical measurements are referenced. However, measurements are referenced. However, the original definition of ground actually the original definition of ground actually referred to the ground. This ground is referred to the ground. This ground is called earth ground.called earth ground.

Figure 8-12: Power Transmission System

Figure 8-13: Grounds on IC Chips

Remember that ESD is destructive and EMI is not.

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Know the best protection for a computer system during an electrical storm.

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A boot-sector virus - This type of virus copies itself onto the boot sector of floppy and hard disks. The virus replaces the disk’s original boot-sector code with its own code. This allows it to be loaded into memory before anything else is loaded. Once in memory, the virus can spread to other disks.

There are basically three types of viruses, based on how they infect a computer system:

(continued)

A file infector - File infectors are viruses that add their virus code to executable files. After the file with the virus is executed, the virus spreads to other executable files. A similar type of virus, called a macro virus, hides in the macro programs of word processing document files. These files can be designed to load when the document is opened or when a certain key combination is entered. In addition, these types of viruses can be designed to stay resident in memory after the host program has been exited (similar to a TSR program), or they might just stop working when the infected file is terminated.

There are basically three types of viruses, based on how they infect a computer system:(continued)

(continued)

A Trojan horse - This type of virus appears to be a legitimate program that might be found on any system. Trojan horse viruses are more likely to do damage by destroying files, and they can cause physical damage to disks.

There are basically three types of viruses, based on how they infect a computer system: (continued)

Know how the different types of viruses attack the system.

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Hard disk controller failures.

Typical virus symptoms include the following:

Disks continue to be full even when files have been deleted.

System cannot read write-protected disks.

The hard disk stops booting and files are corrupted.

The system will boot to floppy disk, but will not access the HDD.

An Invalid Drive Specification message usually displays when attempting to access the C: drive.

(continued)

CMOS settings continually revert to default even though the system board battery is good.

Typical virus symptoms include the following:(continued)

System operation slows down noticeably.

Blank screen when booting (flashing cursor).

Windows crashes.

The hard drive is set to DOS compatibility, and 32-bit file access suddenly stops working.

Network data transfers and print jobs slow down dramatically.

Files change size for no apparent reason.

Know how viruses are spread.

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A customer calls you to his site complaining that the wide-carriage, dot-matrix printer in his accounting department is running very slowly and that they cannot get all their invoices printed for today’s shipping purposes. When you check their print queue, you see that the print jobs for the invoices are stacked up in the queue but are being processed. The accounting manager tells you that they typically don’t have any problems getting their invoices printed and that nothing out of the ordinary has been done to the computer to make it slow down. What items should you check to determine the cause of the slowdown?

KEY POINTSKEY POINTS

Cleaning is a major part of keeping a computer system healthy. Therefore, the technician’s tool kit should also contain a collection of cleaning supplies. Along with hand tools, it will need a lint-free, soft cloth (chamois) for cleaning the plastic outer surfaces of the system.


The environment around a computer system and the manner in which the computer is used determine greatly how many problems it will have. Occasionally dedicating a few moments of care to the computer can extend its Mean Time Between Failures (MTBF) period considerably. This activity, involving maintenance not normally associated with a breakdown, is called Preventive Maintenance (PM).


Unlike hard-disk drives, floppy drives are at least partially open to the atmosphere, and they may be handled on a regular basis. This opens floppy-disk drives to a number of maintenance concerns not found in hard-disk drives. Also, the removable disks are subject to extremes in temperature, exposure to magnetic and electromagnetic fields, bending, and airborne particles that can lead to information loss.


Input peripherals generally require very little in the way of preventive maintenance. An occasional dusting and cleaning should be all that’s really required.


Because printers tend to be much more mechanical than other types of computer peripherals, they require more effort to maintain. Printers generate pollutants, such as paper dust and ink droplets, in everyday operation. These pollutants can build up on mechanical parts and cause them to wear. As the parts wear, the performance of the printer diminishes. Therefore, printers require periodic cleaning and adjustments to maintain good performance.


Digital systems tend to be sensitive to power variations and losses. Even a very short loss of electrical power can shut a digital computer down, resulting in a loss of any current information that has not been saved to a mass storage device.


Uninterruptible power supplies are battery-based systems that monitor the incoming power and kick in when unacceptable variations occur in the power source. The term UPS is frequently used to describe two different types of power backup systems.


In most IBM compatibles, there are only two potentially dangerous areas. One of these is inside the CRT display, and the other is inside the power supply unit. Both of these areas contain electrical voltage levels that are lethal. However, both of these areas reside in self-contained units, and you will usually not be required to open either unit.


Laser printers contain many hazardous areas. The laser light can be very damaging to the human eye. In addition, there are multiple high-voltage areas in the typical laser printer, and a high-temperature area to contend with as well.


Most computer components contain some level of hazardous substances. Printed circuit boards consist of plastics, precious metals, fiberglass, arsenic, silicon, gallium, and lead. CRTs contain glass, metal, plastics, lead, barium, and rare earth metals. Batteries from portable systems can contain lead, cadmium, lithium, alkaline manganese, and mercury.


Electrostatic Discharges (ESD) are the most severe form of Electromagnet Interference (EMI). The human body can build up static charges that range up to 25,000 volts. These buildups can discharge very rapidly into a electrically grounded body or device. Placing a 25,000-volt surge through any electronic device is potentially damaging to it.


In general, MOS devices are sensitive to voltage spikes and static electricity discharges. This can cause many problems when you have to replace MOS devices, especially Complementary-Symmetry Metal Oxide Semiconductor (CMOS) devices. The level of static electricity present on your body is high enough to destroy the inputs of a CMOS device if you touch its pins with your fingers.


The term ground is often a source of confusion for the novice, because it actually encompasses a collection of terms. Generically, ground is simply any point from which electrical measurements are referenced. However, the original definition of ground actually referred to the ground. This ground is called earth ground.

REVIEW QUESTIONSREVIEW QUESTIONS

List the two most dangerous areas of a typical microcomputer system, and explain why they are so dangerous.

11


Name three devices used to minimize ESD in the repair area.

22


The best general-purpose cleaning tool for computer equipment is _______.

33


List at least three environmental conditions that can adversely affectmicrocomputer equipment.

44


A short undervoltage condition, lasting milliseconds, is called ________.

55


Are there any restrictions on disposing of a spent toner cartridge?

66


Which type of IC device is most likely to be damaged by ESD?

77


Can an effective ESD strap be constructed by simply wrapping a grounded bare wire around your wrist?

88


What is the most effective method of dealing with EMI problems?

99


The best method of protecting computer equipment from a thunderstorm is to _______.

1010


The best method for transporting electronic devices is _________.

1111


List computer-related PM items that should be performed annually.

1212


Name two characteristics that should be checked carefully before purchasing a UPS for a given computer system.

1313


Describe the normal duration of a voltage spike.

1414


Once a virus has infected a computer, where does it normally reside?

1515

EXAM QUESTIONSEXAM QUESTIONS

Do viruses normally attack the system’s CMOS settings?

a. Yes, this is how a virus attacks most computers.b. No, viruses do not normally attack CMOS settings.c. Yes, this is how viruses attack all computers.d. No, viruses never attack CMOS settings.

11


How are most computer viruses spread from computer to computer?

a. By downloading programs from networksb. By sharing infected files between individualsc. By not formatting disks before used. By transferring files over modems

22


What is the most common cause of ESD in microcomputer systems?

a. Moving peopleb. High humidityc. Rubber matsd. Grounded power supply cables

33


Where would it be inappropriate to use an ESD wrist strap?

a. While working on hard-disk drivesb. While working on system boardsc. While working on CRT video monitorsd. While working on printers

44


What is one of the best methods for protecting computer systems from ESD?

a. A water and fabric softener solutionb. A water and ammonia solutionc. A water and bleach solutiond. A hydrogen tetrachloride solution

55


A short overvoltage occurrence (nanoseconds) is called ________.

a. a spikeb. a surgec. a brownoutd. a sag

66


ESD is most likely to occur during periods of _________.

a. low humidityb. high humidityc. medium humidityd. rain

77


The best protection against power-failure data loss is _______.

a. a tape backupb. a surge suppresserc. a UPSd. a line filter

88


Define a voltage sag.

a. An overvoltage condition that lasts for a few millisecondsb. An undervoltage condition that lasts for an extended periodc. An overvoltage condition that lasts for an extended periodd. An undervoltage condition that lasts for a few milliseconds

99


The most effective grounding system for a microcomputer is _________.

a. an ESD wrist or ankle strapb. the safety ground plug at a commercial AC receptaclec. the ground plane of the system boardd. the chassis ground provided by brass standoffs

1010

OBJECTIVES

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