chapter 4

4CHAPTER

Electricity and Power Supplies

his chapter focuses on the power supply,which provides power to all other compo-

nents inside the computer case. To troubleshootproblems with the power system of a PC, youneed a basic understanding of electricity. Thischapter begins by describing the measurementsof electricity and the form in which it comes toyou as house current. The chapter then addressesthe power supply, backup power sources, andhow to change a defective power supply. Finally,it introduces you to form factors and explainshow Energy Star devices save energy.

In this chapter, you will learn:

• How electricity is measured

• How to protect your computersystem against damaging changesin electrical power

• About different form factors andcomputer cases

• How to detect and correct powersupply problems

• About Energy Star specifications

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Copyright © 2004 by Course Technology. All rights reserved.This publication is protected by federal copyright law. No part of this publication

Measures and Properties of Electricity

Electrical energy has properties that you can measure in various ways. These mea-surements are listed in Table 4-1.

See Appendix E, “Electricity and Multimeters,” for an explanation of how volts, amps, ohms, andwatts measure the four properties of electricity.

Unit Measures Computer Example

Volt (for example, 110 V) Potential difference in acircuit

An AT power supplyprovides four separatevoltages: +12 V, –12 V,+5 V, and –5 V. An ATXpower supply providesthese voltages and +3.3 Vas well.

Amp or ampere (for example, 1.5 A) Electrical current A 17-inch monitorrequires less than 2 A tooperate. A small laserprinter uses about 2 A. ACD-ROM drive uses about1 A.

Ohm (for example, 20 �) Resistance Current can flow intypical computer cablesand wires with aresistance of near zero �.

Watt (for example, 20 W) Power (watts arecalculated by multiplyingvolts by amps)

A computer power supplyis rated at 200 to 600 W.

Table 4-1 Measures of electricity

While volts and amps are measured to determine their value, watts are calculated by multiplyingvolts by amps.

116 CHAPTER 4 Electricity and Power Supplies



AC and DC

Electricity can be either AC, alternating current, or DC, direct current. Alternatingcurrent (AC) cycles, or oscillates, back and forth rather than traveling in only onedirection. House current in the United States oscillates 60 times in one second(60 hertz), changing polarity from +110 V to –110 V and causing current to flow indifferent directions, depending on whether it’s positive or negative in the cycle. AC isthe most economical way to transmit electricity to our homes and workplaces. Bydecreasing current and increasing voltage, we can force alternating current to travelgreat distances. When alternating current reaches its destination, it is made more suit-able for driving our electrical devices by decreasing voltage and increasing current.

Direct current (DC) travels in only one direction and is the type ofcurrent that most electronic devices require, including computers. Arectifier is a device that converts alternating current to direct current.A transformer is a device that changes the ratio of current to voltage.Large transformers reduce the high voltage on power lines coming toyour neighborhood to a lower voltage before the current enters yourhome. The transformer does not change the amount of power in this

closed system; if it decreases voltage, then it increases current. The overall powerstays constant, but the ratio of voltage to current changes.

A computer power supply changes and conditions the house electrical current inseveral ways, functioning as both a transformer and a rectifier (see Figure 4-1). Itsteps down the voltage from the 110-volt house current to 3.3, 5, and 12 volts, or to5 and 12 volts, and changes incoming alternating current to direct current, which thecomputer and its peripherals require. The monitor, however, receives the full 110volts of AC voltage, converting that current to DC.

Vents for cooling fan

Label lists voltages formotherboard connector

External power source

Connector for floppy drive

Connectors for hard drivesand other drives

P1 power connector to motherboard

Figure 4-1 Computer power supply with connections

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✔✔ A+ EXAM TIPThe A+ Core exam expectsyou to know the differencebetween a rectifier and atransformer.

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Direct current flows in only one direction, from hot to ground. For a PC, a linemay be either +5 or –5 volts in one circuit, or +12 or –12 volts in another circuit,depending on whether the circuit is on the positive side or negative side of the poweroutput. Several circuits coming from the power supply accommodate differentdevices with different power requirements.

Hot, Neutral, and Ground

When AC comes from the power source at the power station to your house, it travelson a hot line and completes the circuit from your house back to the power source ona neutral line, as shown in Figure 4-2.

Neutral

HotHotNeutral

Neutra

l

Hot

HotNeutral

Power station

GroundGround

Ground

Ground

Hot contacts neutralin the lamp

Figure 4-2 Normally hot contacts neutral to make a closed circuit in the controlled environment ofan electrical device such as a lamp. An out-of-control contact is called a short, and theflow of electricity is then diverted to the ground.

When the two lines reach your house and enter an electrical device, such as alamp or radio, electricity flows through the device to complete the circuit betweenthe hot line and the neutral line. The device contains resistors and other electricalcomponents that control the flow of electricity between the hot and neutral lines. The


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hot source seeks and finds ground by returning to the power station on the neutralline.

A short circuit, or a short, occurs when uncontrolled electricity flows from the hotline to the neutral line or from the hot line to ground. Electricity naturally finds theeasiest route to ground. Normally that path is through some device that controls thecurrent flow and then back through the neutral line. If an easier path (one with lessresistance) is available, the electricity follows that path. This can cause a short, a sud-den increase in flow that can also create a sudden increase in temperature—enoughto start a fire and injure both people and equipment. Never put yourself in a positionwhere you are the path of least resistance between the hot line and ground!

A fuse is a component included in a circuit and designed to prevent too much cur-rent from flowing through the circuit. A fuse is commonly a wire inside a protectivecase, which is rated in amps. If too much current begins to flow, the wire gets hotand eventually melts, breaking the circuit, as an open switch would, and stopping thecurrent flow. Many devices have fuses, which can be easily replaced when damaged.

To prevent the uncontrolled flow of electricity from continuing indefinitely, whichcan happen because of a short, the neutral line is grounded. Grounding a line meansthat the line is connected directly to the earth, so that, in the event of a short, the elec-tricity flows into the earth and not back to the power station. Grounding serves as anescape route for out-of-control electricity. The earth is at no particular state of chargeand so is always capable of accepting a flow of current.

The neutral line to your house is grounded many times along its way (in fact, ateach electrical pole) and is also grounded at the breaker box where the electricityenters your house. You can look at a three-prong plug and see the three lines: hot,neutral, and ground (see Figure 4-3). Generally, electricians use green or bare wirefor the ground wire, white for neutral, and black for hot in home wiring for 110-voltcircuits. In a 220-volt circuit, black and red are hot, white is neutral, and green orbare is ground. To verify that a wall outlet is wired correctly, use a simple receptacletester, as shown in Figure 4-4.

Beware of the different uses of black wire. In PCs, black is used for ground, but in home wiring,black is used for hot!

Even though you might have a three-prong outlet in your home, the ground plugmight not be properly grounded. To know for sure, test the outlet with areceptacle tester.


4



Figure 4-3 A three-prong plug showing hot, neutral, and ground

Figure 4-4 Use a receptacle tester to verify that hot, neutral, and ground are wired correctly


Hot

Neutral

Ground



It’s very important that PC components be properly grounded. Never connect a PC to an outlet oruse an extension cord that doesn’t have the third ground plug. The third line can prevent a shortfrom causing extreme damage. In addition, the bond between the neutral and ground helps elim-inate electrical noise (stray electrical signals) within the PC sometimes caused by other electricalequipment sitting very close to the computer.

Some Common Electronic Components

Understanding what basic electronic components make up a PC and how they workis important. Basic electronic components in a PC include transistors, capacitors,diodes, ground, and resistors. Figure 4-5 shows the symbols for these components.

Resistor

Diode

Capacitor

Transistor

Ground

Figure 4-5 Symbols for some electronic components and ground

Materials used to make these and other electronic components can be:

� Conductors. Material that easily conducts electricity, such as gold or copper� Insulators. Material that resists the flow of electricity, such as glass or ceramic� Semiconductors. Material such as silicon whose ability to conduct electricity,

when a charge is applied, falls between that of a conductor and an insulator

A transistor is an electronic device that can serve as a gate or switch for an electri-cal signal and can amplify the flow of electricity. Invented in 1947, the transistor ismade of three layers of semiconductor material. A charge (either positive or negative,depending on the transistor’s design) placed on the center layer can cause the twoouter layers of the transistor to complete a circuit to create an “on” state. Anopposite charge placed on the center layer can make the reverse happen, causing thetransistor to create an “off” state. Manipulating these charges to the transistor allowsit to hold a logic state, either on or off (translated to binary 0 or 1). When the transis-tor maintains this state, it requires almost no electrical power. Because the initialcharge sent to the transistor is not as great as the resulting current that the transistorcreates, sometimes a transistor is used as a small amplifier. The transistor is the basicbuilding block of an integrated circuit (IC), which is used to build a microchip.


4



A capacitor is an electronic device that can hold an electrical charge for a period oftime and can smooth the uneven flow of electricity through a circuit. Capacitorsinside a PC power supply create the even flow of current the PC needs. Capacitorsmaintain their charge long after current is no longer present, which is why the insideof a power supply can be dangerous even when it is unplugged.

A diode is a semiconductor device that allows electricity to flow in only one direc-tion. (A transistor contains two diodes.) One to four diodes used in various configura-tions can be used to convert AC to DC. Singularly or collectively, depending on theconfiguration, these diodes are called a rectifier.

A resistor is an electronic device that limits the amount of current that can flowthrough it.

Protecting Your Computer System

Now that you have learned some basic information about how electricity is measuredand managed, understanding how power is supplied to a computer will be easier. Butfirst, let’s look at ways to protect your computer system. As you read the rest of thechapter and when you work on the projects at the end of this chapter, you will beginto look inside a computer and start taking it apart and putting it back together.While working on a computer, it is possible to harm both the computer and yourself.The most common accident when someone attempts to fix a computer problem iserasing software or data. Experimenting without knowing what you are doing cancause damage. You can take many safety precautions to prevent these sorts of acci-dents, as well as the ones that put you in physical danger. Here are a few generalsafety precautions to keep in mind:

� Make notes as you work so that you can backtrack later if necessary.� When unpacking hardware or software, remove the packing tape and cello-

phane from the work area as soon as possible.� Keep components away from your hair and clothing.� Keep screws and spacers orderly and in one place, such as a cup or tray.� Don’t stack boards on top of each other: You could accidentally dislodge a chip

this way.� When handling motherboards and expansion cards, don’t touch the chips on

the boards. Hold expansion cards by the edges. Don’t touch any soldered com-ponents on a card, and don’t touch chips or edge connectors unless it’sabsolutely necessary.

� Don’t touch a chip with a magnetized screwdriver.� Don’t use a graphite pencil to change DIP switch settings, because graphite is a

conductor of electricity, and the graphite can lodge in the switch. � In a classroom environment, after you have reassembled everything, have your

instructor check your work before you put the cover back on and power up.

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� Always turn off a computer before moving it. A computer’s hard drive alwaysspins while it is on, unless it has a sleep mode. Therefore, it is important not tomove, kick, or jar a computer while it is running.

� To protect disks, keep them away from magnetic fields, heat, and extreme cold.Don’t open the shuttle window on a floppy disk or touch the disk’s surface.

You will learn about additional safety precautions in the remainder of this section.

To protect both yourself and the equipment when working inside a computer, turn off the power,unplug the computer, and always use a ground bracelet (which you will learn more about later).Never touch the inside of a computer that is turned on. In addition, consider the monitor andthe power supply to be “black boxes.” Never remove the cover or put your hands inside thisequipment unless you know about the hazards of charged capacitors and have been trained todeal with them. Both the power supply and the monitor can hold a dangerous level of electricityeven after you turn them off and disconnect them from a power source. The power supply andmonitor contain enough power to kill you, even when they are unplugged.

Static Electricity

Electrostatic discharge (ESD), commonly known as static electricity, is an electricalcharge at rest. A static charge can build up on the surface of an ungrounded conduc-tor and on nonconductive surfaces such as clothing or plastic. When two objects withdissimilar electrical charges touch, static electricity passes between them until the dis-similar charges become equal. To see how this works, turn off the lights in a room,scuff your feet on the carpet, and touch another person. Occasionally you can seeand feel the charge in your fingers. If you can feel the charge, then you discharged atleast 3,000 volts of static electricity. If you hear the discharge, then you released atleast 6,000 volts. If you see the discharge, then you released at least 8,000 volts ofESD. A charge of much less than 3,000 volts can damage electronic components. Youcan touch a chip on an expansion card or motherboard, damage the chip with ESD,and never feel, hear, or see the discharge.

ESD can cause two types of damage in an electronic component:catastrophic failure and upset failure. A catastrophic failure destroysthe component beyond use. An upset failure damages the componentso that it does not perform well, even though it may still function tosome degree. Upset failures are more difficult to detect because theyare not as easily observed.

A monitor can also damage components with ESD. Do not place or store expansion cards on topof or next to a monitor, which can discharge as much as 29,000 volts onto the screen.

✔✔ A+ EXAM TIPThe A+ Core exam empha-sizes that you should knowhow to protect computerequipment as you work on it.

Protecting Your Computer System 123

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To protect the computer against ESD, always ground yourself before touching elec-tronic components, including the hard drive, motherboard, expansion cards, proces-sors, and memory modules. Ground yourself and the computer parts, using one ormore of the following static control devices or methods:

� Ground bracelet or static strap. A ground bracelet is a strap you wear aroundyour wrist. One end attaches to a grounded conductor such as the computercase or a ground mat or plugs into a wall outlet. (Only the ground prong makesa connection!) The bracelet also contains a resistor that prevents electricityfrom harming you. Figure 4-6 shows a ground bracelet.

Figure 4-6 A ground bracelet, which protects computer components from ESD, can clip to the side ofthe computer case and eliminates ESD between you and the case

� Ground mats. Ground mats can come equipped with a cord to plug into a walloutlet to provide a grounded surface on which to work. If you lift the compo-nent off the mat, it is no longer grounded and is susceptible to ESD. Figure 4-7shows a ground mat.


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Alligator clip connectsground bracelet tocomputer case

Resistor that preventsthe flow of electricity



Snaps toconnectground bracelet

Ground bracelet

Ground mat

To ground linein wall outlet

Ground braceletsnaps to mat

Figure 4-7 A ground bracelet can be connected to a ground mat, which is grounded by the wall outlet

� Static shielding bags. New components come shipped in static shieldingbags.These bags are a type of Farady Cage, which is any device that protectsagainst an electromagnetic field. Save the bags to store other devices that arenot currently installed in a PC. When working on a PC, you can also lay com-ponents on these bags (see Figure 4-8).

Figure 4-8 Static shielding bags help protect components from ESD

The best way to guard against ESD is to use a ground bracelet together with aground mat. Consider a ground bracelet essential equipment when working on acomputer. However, if you are in a situation where you must work without one,touch the computer case or the power supply before you touch a component. Whenpassing a chip to another person, ground yourself and then touch the other personbefore you pass the chip. Leave components inside their protective bags until you areready to use them. Work on hard floors, not carpet, or use antistatic spray on the


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carpets. Generally, don’t work on a computer if you or the computer have just comein from the cold, because the potential for ESD is higher.

Besides using a ground mat, you can also create a ground for the computer case by leaving thepower cord to the case plugged into the wall outlet. This is safe enough because the power isturned off when you work inside the case. However, if you happen to touch an exposed area ofthe power switch inside the case, you may get a shock. Because of this risk, this book directsyou to unplug the power cord to the PC before you work inside the case.

There are exceptions to the rule of always being grounded when you work with PCs. You don’twant to be grounded when working inside a monitor, with a power supply, or with high-voltageequipment such as a laser printer. These devices maintain high electrical charges, even when thepower is turned off. Inside a monitor case, the electricity stored in capacitors poses substantialdanger. When working inside a monitor, you don’t want to be grounded, because you would pro-vide a conduit for the voltage to discharge through your body. In this situation, be careful notto ground yourself. The situation is similar when working with a power supply. Don’t wear aground bracelet when working inside these devices, because you don’t want to be the ground forthese charges!

EMI (Electromagnetic Interference)

Another phenomenon that can cause electrical problems with computers is electro-magnetic interference (EMI). EMI is caused by the magnetic field produced as a sideeffect when electricity flows. EMI in the radio frequency range, which is called radiofrequency interference (RFI), can cause problems with radio and TV reception. Datain data cables that cross an electromagnetic field can become corrupted, causingcrosstalk. Using shielded data cables covered with a protective material can partiallycontrol crosstalk. Power supplies are also shielded to prevent them from emitting EMI.

PCs can emit EMI to other nearby PCs, which is one reason a computer needs to be inside a case.To help cut down on EMI between PCs, always install face plates in empty drive bays or slot cov-ers over empty expansion slots.

If mysterious, intermittent errors persist on a PC, one thing to suspect is EMI. Trymoving the PC to a new location. If the problem continues, try moving it to alocation that uses an entirely different electric circuit. Using an inexpensive AM radiois one simple way to detect the presence of EMI. Turn the tuning dial away from astation into a low-frequency range. With the radio on, you can hear the static thatEMI produces. Try putting the radio next to several electronic devices to detect theEMI they emit.

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If EMI in the electrical circuits coming to the PC poses a significant problem, youcan use a line conditioner to filter the electrical noise causing the EMI. Line condi-tioners are discussed later in the chapter.

Surge Protection and Battery Backup

In addition to protecting your PC against ESD and EMI, you need to consider howpower coming into a computer is regulated. A wide range of devices on the marketfilter the AC input to computers and their peripherals (that is, condition the AC inputto eliminate highs and lows) and provide backup power when the AC fails. Thesedevices, installed between the house current and the computer, fall into three generalcategories: surge suppressors, power conditioners, and uninterruptible power sup-plies (UPSs). All these devices should have the UL (Underwriters Laboratory) logo,which ensures that the laboratory, a provider of product safety certification, hastested the device.

Surge suppressors protect equipment against sudden changes in power level, suchas spikes from lightning strikes. Power conditioners and uninterruptible power sup-plies condition the power passing through them (that is, alter it to provide continu-ous voltages). Both provide a degree of protection against spikes (temporary voltagesurges) and raise the voltage when it drops during brownouts (temporary voltagereductions). These devices are measured by the load they support in watts, volt-amperes (VA), or kilovolt-amperes (kVA).

To determine the VA required to support your system, multiply the amperage ofeach component by 120 volts and then add up the VA for all components. Forexample, a 17-inch monitor has “1.9 A” written on its back, which means 1.9 amps.Multiply that value by 120 volts, and you see that the monitor requires 228 VA. APentium PC with a 17-inch monitor and tape backup system requires about 500 VAor 500 watts of support.

Surge Suppressors

A surge suppressor, also called a surge protector, provides a row of power outletsand an on/off switch that protects equipment from overvoltages on AC power linesand telephone lines. A surge suppressor might be a shunt type that absorbs the surge,a series type that blocks the surge from flowing, or a combination of the two. Asuppressor is measured by clamping voltage, a term that describes the let-throughvoltage, or in joules, a measure of the amount of energy a surge suppressor canabsorb. Surge suppressors can come as power strips (note that not all power stripshave surge protection), wall-mounted units that plug into AC outlets, or consolesdesigned to sit beneath the monitor on a desktop. Some provide RJ-11 telephonejacks to protect modems and fax machines from spikes.

A data line protector serves the same function for your telephone line to yourmodem that a surge suppressor does for the electrical lines. Telephone lines carry asmall current of electricity and need protection against spikes, just as electrical lines

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do. The let-through rating for a data line protector for a phone line should be nomore than 260 volts.

Whenever a power outage occurs, unless you have a reliable power conditioner or UPS installed,unplug all power cords to the PC, printers, monitors, and the like. Sometimes when the powerreturns, sudden spikes are accompanied by another brief outage. You don’t want to subject yourequipment to these surges. When buying a surge suppressor, look for those that guaranteeagainst damage from lightning and that reimburse for equipment destroyed while the surge sup-pressor is in use.

Surge suppressors are not always reliable, and once the fuse inside the suppressor blows, a surgesuppressor no longer protects equipment from a power surge. It might continue to provide powerwithout warning that you have lost protection.

When shopping for a surge protector, consider the let-through voltage rating, joules rating(more than 600 joules), warranty for connected equipment, line noise filtering, and phone lineprotection. Also, when you plug in a surge protector, know that if the protector is not groundedusing a three-prong outlet, the protector cannot do its job.

Power Conditioners

In addition to providing protection against spikes, power conditioners also regulate,or condition, the power, providing continuous voltage during brownouts. These volt-age regulators, sometimes called line conditioners, can come as small desktop units.

These electricity filters are a good investment if the AC in your community suffersexcessive spikes and brownouts. However, a device rated under 1 kVA will probablyprovide corrections only for brownouts, not for spikes. Line conditioners, like surgesuppressors, provide no protection against a total blackout (complete loss of power).

Uninterruptible Power Supply

Unlike a power conditioner, the uninterruptible power supply (UPS) provides backuppower in the event that the AC fails completely. The UPS also offers some filtering ofthe AC. The power supplies in most computers can operate over a wide range of elec-trical voltage input; however, operating the computer under these conditions forextended periods of time can shorten not only the power supply’s life, but also thecomputer’s. UPSs offer these benefits:

� Condition the line for both brownouts and spikes� Provide backup power during a blackout� Protect against very high spikes that could damage equipment

A UPS device suitably priced for personal computer systems is designed as either astandby device, an inline device, or a line-interactive device (which combines features


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of the first two). Several variations of these three types of UPS devices are on the mar-ket at widely varying prices.

A common UPS device is a rather heavy box that plugs into an AC outlet and pro-vides one or more outlets for the computer and its peripherals (see Figure 4-9). It hasan on/off switch, requires no maintenance, and is very simple to install.

Figure 4-9 Uninterruptible power supply (UPS)

The Smart UPS

Some UPSs can be controlled by software from a computer, to allow additional func-tionality. For example, from the front panel of some UPSs you can check for a weakbattery. If the UPS is a smart UPS (also called an intelligent UPS), you can performthe same function from utility software installed on your computer. To accommodatethis feature, a UPS must have a serial port or USB connection to the PC and a micro-processor on board. Some tasks this utility software and a smart UPS can do are:

� Diagnose the UPS� Check for a weak battery� Monitor the quality of electricity received� Monitor the percentage of load the UPS is carrying during a blackout� Automatically schedule the weak-battery test or UPS diagnostic test� Send an alarm to workstations on a network to prepare for a shutdown� Close down all servers protected by the UPS during a blackout� Provide pager notification to a facilities manager if the power goes out� After a shutdown, allow for startup from a remote location over phone lines


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Uninterruptible powersupply



Windows NT, Windows 2000, and Windows XP offer support for smart UPSs. Youcan monitor and control the devices from the UPS dialog box accessible through theControl Panel. Microsoft and American Power Conversion (APC), a leading manufac-turer of UPSs, developed the Windows 2000 controls.

What to Consider When Buying a UPS

When you purchase a UPS, cost often drives the decision about how much and whatkind of protection you buy. However, do not buy an inline UPS that runs at fullcapacity. A battery charger operating at full capacity produces heat, which canreduce the battery’s life. The UPS rating should exceed your total VA or wattage out-put by at least 25 percent. Also, be aware of the degree of line conditioning that theUPS provides. Consider the warranty and service policies as well as the guarantee theUPS manufacturer gives for the equipment that the UPS protects. Table 4-2 lists someUPS manufacturers.

Manufacturer Web Site

MGE UPS Systems www.mgeups.com

American Power Conversion Corp. (APC) www.apcc.com

Tripp Lite www.tripplite.com

Belkin Components www.belkin.com

Invensys www.powerware.com

Liebert Corporation www.liebert.com

Para Systems, Inc. www.minuteman-ups.com

Toshiba International Corp. www.tic.toshiba.com

Table 4-2 UPS manufacturers

The Computer Case and Form Factors

Power supplies and computer cases are often sold together and must be compatiblewith each other. Also, the power supply and case must fit the motherboard. For thesereasons, you can now turn your attention to the computer case. When you puttogether a new system, or replace components in an existing system, the form factorsof the motherboard, power supply, and case must all match. The form factordescribes the size, shape, and general makeup of a hardware component.

When you are deciding which form factor to use, the motherboard drives thedecision because it determines what the system can do. After you’ve decided to use acertain form factor for the motherboard, then you must use the same form factor for

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the case and power supply. Using a matching form factor for the power supply andcase assures you that:

� The motherboard fits in the case.� The power supply cords to the motherboard provide the correct voltage, and

the connectors match the connections on the board.� The holes in the motherboard align with the holes in the case for anchoring the

board to the case.� Holes in the case align with ports coming off the motherboard.� For some form factors, wires for switches and lights on the front of the case

match up with connections on the motherboard.

Case, Power Supply, and Motherboard Form Factors

Several form factors apply to power supplies, cases, and mother-boards: the AT, ATX, LPX, NLX, and backplane systems. Each ofthese form factors has several variations. The four most commonform factors used on personal computers today are the AT, Baby AT,ATX, and Mini-ATX. The most popular form factor is the ATX.This form factor and earlier, less common, and up-and-coming formfactors are discussed next.

AT Form Factor

The AT form factor, sometimes called full AT, is used on older motherboards thatmeasure 12" × 13.8". This form factor uses the full-size AT cases that the originalIBM AT (Advanced Technology) personal computer used. A smaller, more conve-nient version of AT called the Baby AT came later. Full AT motherboards cannot beused with smaller AT cases or with newer ATX cases. Their dimensions andconfiguration make full AT systems difficult to install, service, and upgrade. Anotherproblem with the AT form factor is that the CPU is placed on the motherboard infront of the expansion slots; long cards might not fit in these slots because they willbump into the CPU. You can visualize this problem by looking at the AT mother-board in Figure 4-10.

Recall that power supplies for AT systems supply +5, –5, +12, and –12 volts to themotherboard and other components. The AT board uses two power connections, theP8 connector and the P9 connector (see Figure 4-11). Most manufacturers no longerproduce full AT boards.

✔✔ A+ EXAM TIPThe A+ Core exam expectsyou to recognize and knowthe more important featuresof the AT and ATX boards.

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Figure 4-10 The CPU on the AT motherboard sits in front of the expansion slots

Figure 4-11 ATX uses a single P1 power connector (A), but AT-type motherboards use P8 and P9 powerconnectors (B)


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RAM slots withtwo SIMMS

Connections topower supply

16-bit ISAexpansionslots (4)

PCI expansionslots (3)

CPU and fan

Keyboard port

P1 on an ATX motherboard

(A)

P8 and P9 on an AT motherboard

(B)



Baby AT Form Factor

Improved flexibility over full AT made Baby AT the industry standard form factorfrom about 1993 to 1997. Power supplies designed for the Baby AT form factorblow air out of the computer case. At 13" × 8.7", Baby AT motherboards are smallerthan full AT motherboards and fit in many types of cases, including newer ATXcases designed to provide backward compatibility. The design of Baby AT mother-boards did not resolve the problem with the position of the CPU in relation toexpansion slots. In addition, because of the motherboard’s configuration andorientation within the case, drives and other devices are not positioned close to theirconnections on the motherboard. This means that cables might have to reach acrossthe motherboard and not be long enough.

ATX Form Factor

ATX is the most commonly used form factor today. It is an open, nonproprietaryindustry specification originally developed by Intel in 1995. ATX improved upon ATby making adding and removing components easier, providing greater support forI/O devices and processor technology, and lowering costs. Components on the moth-erboard are arranged so they don’t interfere with each other and for better positioninside the case. Also, the position of the power supply and drives inside the casemakes connecting them to the motherboard easier and makes it possible to reducecable lengths, which can help reduce the potential for EMI and corrupted data. Con-necting the switches and lights on the front of the case to components inside the caserequires fewer wires, making installation simpler and reducing the potentialfor mistakes.

An ATX motherboard measures 12" × 9.6", so it’s smaller than a full AT mother-board. On an ATX motherboard, the CPU and memory slots are rotated 90 degreesfrom the position on the AT motherboard. Instead of sitting in front of the expansionslots, the CPU and memory slots sit beside them, preventing interference with full-length expansion cards (see Figure 4-12).

The ATX power supply and motherboard use a single power connector called theP1 connector that includes, in addition to the voltages provided by AT, a +3.3-voltcircuit for a low-voltage CPU (refer back to Figure 4-11). In addition to the P1 con-nector, one or more auxiliary connectors can be used to supply power to the CPU orCPU fan. Cases designed for Baby AT and LPX cannot accommodate ATX mother-boards and power supplies, although many ATX cases can accommodateBaby AT motherboards.

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Figure 4-12 The CPU on an ATX motherboard sits beside the expansion slots and does not block theroom needed for long expansion cards

An additional difference between AT and ATX systems is that the power supplyfan blows air out of the case rather than into it, which provides better air circulationand cooling for the processor. You’ll learn more about case fans later in the chapter.

Another feature of an ATX motherboard not found on AT boards is a soft switch,sometimes called the soft power feature. Using this feature, an OS, such as Windows98 or Windows 2000/XP, can turn off the power to a system after the shutdown pro-cedure is done. Also, CMOS can be configured to cause a keystroke or network activ-ity to power up the system (wake on LAN). On older AT systems, when the PC isrunning and a user presses the power switch on the front of the case, the power turnsoff abruptly. The operating system has no opportunity to close down gracefully and,on the next power up, the system might have errors. With a soft switch controllingan ATX system and an operating system supporting the feature, if the user pressesthe power switch on the front of the case while the computer is on, the OS goesthrough a normal shutdown procedure before powering off.

In addition to regular ATX, there are several other types of ATX boards. Mini-ATX, a smaller ATX board (11.2" × 8.2"), can be used with ATX cases and powersupplies. MicroATX addresses some technologies that have emerged since the origi-nal development of ATX. FlexATX allows for maximum flexibility in the design ofsystem cases and boards and therefore can be a good choice for custom systems.


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P1 power connector

Slot 1 for Pentium III withsupporting braces

16-bit ISA expansion slot

Five PCI expansion slots

AGP slot

Parallel portTwo serial portsTwo USB ports

Keyboard andmouse ports

Four RAM slots with oneDIMM installed



NLX Form Factor

NLX is a form factor for low-end personal computer motherboards and is used withlow-profile cases. In NLX systems, the motherboard has only one expansion slot, inwhich a riser card, or bus riser, is mounted (see Figure 4-13). Expansion cards aremounted on the riser card, and the card also contains connectors for the floppy andhard drives. The motherboard itself includes a low-end video controller. The NLXform factor is designed to be flexible and to use space efficiently.

MotherboardREAR

Ports on rear of board forperipheral devices

Memorymodules

FRONT

CPU with heat sinkattached

Riser card for expansion slotsand other connectors

Two PCIslots

Two ISAslots

Figure 4-13 The NLX form factor uses a riser card that connects to the motherboard. The riser cardprovides expansion slots for the expansion cards.

LPX and Mini-LPX Form Factors

Western Digital originally developed LPX and Mini-LPX, which each have a risercard similar to NLX systems, and are often used in low-cost systems sold in largeelectronics stores. Difficult to upgrade, they cannot handle the size and operatingtemperature of today’s faster processors. In addition, a manufacturer often makesproprietary changes to the standard LPX motherboard design, forcing you to useonly the manufacturer’s power supply. LPX and Mini-LPX use small cases calledlow-profile cases and slimline cases, which the next section discusses.

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Backplane Systems

Backplane systems do not use a true motherboard. The backplane is a board thatnormally sits against the back of a proprietary case with slots on it for other cards.Active backplanes contain no circuits other than bus connectors and some buffer anddriver circuits. Passive backplanes contain no circuitry at all; the circuits are all on amothercard, a circuit board that plugs into the backplane and contains a CPU. Thesesystems are generally not used in personal computers. Passive backplanes are some-times used for industrial rack-mounted systems and high-end file servers. A rack-mounted system is not designed for personal use, and often several of these systemsare mounted in cases stacked on a rack for easy access by technicians.

Types of Cases

Several types and sizes of cases are on the market for each form factor. The computercase, sometimes called the chassis, houses the power supply, motherboard, expansioncards, and drives. The case has lights and switches on the front panel that can beused to control and monitor the PC. Generally, the larger the case, the larger thepower supply and the more amps it carries. These large cases allow for the extraspace and power needed for a larger number of devices, such as multiple hard drivesneeded in a server.

Cases for personal computers and notebooks fall into three major categories: desk-top cases, tower cases, and notebook cases.

Desktop Cases

The classic case with four drive bays and around six expansion slots that sits on yourdesktop doing double duty as a monitor stand is called a desktop case. The mother-board sits on the bottom of a desktop case, and the power supply is near the back.Because of the space a desktop case takes, it has fallen out of favor in recent yearsand is being replaced by smaller and more space-efficient cases.

For low-end desktop systems, compact cases, sometimes called low-profile or slim-line cases, follow either the NLX, LPX, or Mini-LPX form factor. Likely to havefewer drive bays, they generally still provide for some expansion. You can see therear of a compact case in Figure 4-14. An LPX motherboard that uses this case has ariser card for expansion cards, which is why the expansion card slots in the figurerun parallel to the motherboard sitting on the bottom of the case.

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Fan

Power cordconnectors

Expansion slots

Keyboard portSerial ports

Printer port

Video port

Figure 4-14 Because the expansion slots are running parallel to the motherboard on the bottom ofthis desktop case, you know a riser card is used

Tower Cases

A tower case can be as high as two feet and has room for several drives. Often usedfor servers, this type of case is also good for PC users who anticipate upgrading,because tower cases provide maximum space for working inside a computer and mov-ing components around. Variations in tower cases include the minitower, midsizetower, and full-size tower.

Midsize towers, also called miditowers, are the most popular. They are midrangein size and generally have around six expansion slots and four drive bays, providingmoderate potential for expansion. The minitower, also called a microtower, is thesmallest type of tower case and does not provide room for expansion. Figure 4-15shows a minitower that accommodates a Baby AT or a full ATX system. Full-sizetowers are used for high-end personal computers and servers. They are usually builtto accommodate ATX, Mini-ATX, and Baby AT systems. Figure 4-16 shows exam-ples of each of the three main tower sizes, as well as two desktop cases.


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Figure 4-15 Minitower for Baby AT or full ATX motherboard

MinitowerMidsize tower

Full-size tower

Slimline desktopDesktop

Figure 4-16 Tower and desktop cases

Notebook Cases

Notebook cases are used for portable computers that have all the components of adesktop computer. The cost and power of notebook systems varies widely. As withother small systems, notebooks can present difficulties in expansion. The smallestnotebook cases are called subnotebooks. Notebook designs are often highly propri-etary, but are generally designed to conserve space, allow portability, use less power,and produce less heat. The case fan in a notebook usually attaches to a thermometer


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and runs only when temperature needs to be lowered. Additionally, the transformerand rectifier functions of the power supply are often moved to an AC adapter on thepower cable.

In summary, when selecting a computer case, remember that the case needs to fitits intended use. Many different manufacturers make cases and power supplies. Somespecialize in high-end custom systems, while others make a variety of cases, fromrack-mounted servers to low-profile desktops. Table 4-3 lists a few case and powersupply vendors.

Manufacturer Web Site

Alien Media www.alienmedia.com.au/cases

Axxion Group Corporation www.axxion.com

Sunus Suntek www.suntekgroup.com

Enlight Corporation www.enlightcorp.com

PC Power and Cooling www.pcpowerandcooling.com

PCI Case Group www.pcicase.co.uk/menu.htm

Casse Industry Corp. www.kingspao.com

Colorcase www.colorcase.com

Table 4-3 Manufacturers of cases and power supplies for personal computers

Detecting and Correcting Power Supply Problems

If you assemble a PC from parts, most often you purchase a computer case with thepower supply already installed. However, you might need to exchange the powersupply of an existing PC because it is damaged or you need to upgrade to one withmore power. In this section, you will learn how to troubleshoot the power systemand power supply in your computer as well as how to upgrade and installpower supplies.

Upgrading Your Power Supply

Sometimes a power supply upgrade is necessary when you add new devices. If youare installing a hard drive or DVD drive and are concerned that the power supply isnot adequate, test it after you finish the installation. Make as many as possible of thedevices in your system work at the same time. For example, you can make both thenew drive and the floppy drive work at the same time by copying files from one to

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Detecting and Correcting Power Supply Problems 139

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the other. If the new drive and the floppy drive each work independently, but dataerrors occur when both work at the same time, suspect a shortage of electrical power.

If you prefer a more technical approach, you can estimate how much total wattageyour system needs by calculating the watts required for each device and adding themtogether. (Calculate watts by multiplying volts in the circuit by amps required foreach device.) However, in most cases, the computer’s power supply is more than ade-quate if you add only one or two new devices.

Most often you purchase a computer case with a power supply already installed,but you can purchase power supplies separately from cases. Power supplies for micro-computers range from 200 watts for a small desktop computer system to 600 wattsfor a tower floor model that uses many multimedia or other power-hungry devices.Most case vendors also make power supplies (refer back to Table 4-3).

The easiest way to fix a power supply you suspect is faulty is to replace it. You candetermine if the power supply really is the problem by turning off the PC, openingthe computer case, and setting the new power supply on top of the old one. Discon-nect the old power supply’s cords and plug the PC devices into the new power sup-ply. Turn on the PC and verify that the new power supply solves your problembefore installing it.

Follow this procedure to install a power supply:

1. Turn off the power to the computer.

2. Remove all external power cables from the power supply connections.

3. Remove the computer case cover.

4. Disconnect all power cords from the power supply to other devices.

5. Determine which components must be removed before the power supply can besafely removed from the case. You might need to remove the hard drive, severalcards, or the CD-ROM drive. In some cases, you may even need to remove themotherboard.

6. Remove all the components necessary to get to the power supply. Remember toprotect the components from static electricity as you work.

7. Unscrew the screws on the back of the computer case that hold the power sup-ply to the case.

8. Look on the bottom or back of the case for slots that hold the power supply inposition. Often the power supply must be shifted in one direction to free it fromthe slots.

9. Remove the power supply.

10. Place the new power supply in position, sliding it into the slots the old powersupply used.

11. Replace the power supply screws.


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12. Replace all other components.

13. Before replacing the case cover, connect the power cords, turn on the PC, andverify that all is working.

14. Turn off the PC and replace the cover.

In a project at the end of this chapter, you will see additional instructions for tak-ing a computer apart and putting it back together.

Introduction to Troubleshooting

Troubleshooting a PC problem begins with isolating it into one of two categories:problems that prevent the PC from booting and problems that occur after a success-ful boot. Begin by asking the user questions like these to learn as much as you can:

� Please describe the problem. What error messages, unusual displays, or failuresdid you see?

� When did the problem start?� What was the situation when the problem occurred?� What programs or software were you using?� Did you move your computer system recently?� Has there been a recent thunderstorm or electrical problem?� Have you made any hardware, software, or configuration changes?� Has someone else used your computer recently?� Can you show me how to reproduce the problem?

Next, ask yourself, “Does the PC boot properly?” Figure 4-17 shows you the direc-tion to take, depending on the answer. If the screen is blank and the entire system is“dead”—no lights, no spinning drive or fan—then proceed to troubleshoot thepower system.

Recall from Chapter 3 that when POST completes successfully, it sounds a singlebeep indicating that all is well, regardless of whether the monitor is working or evenpresent. If you hear the beep, then the problem is with the video, and the next step isto troubleshoot the video. If you don’t hear the beep or you hear more than one, thenPOST encountered an error. In that case, proceed to troubleshooting the mother-board, a subject Chapter 5 covers.

If an error message appears on the screen, then the obvious next step is to respondto the message. An example of such an error is “Keyboard not present.” If the errormessage occurs as the OS loads, and you don’t understand the message or know howto respond to it, begin by troubleshooting the OS.

If video works but the boot message is confusing or unreadable, then begin to elim-inate the unnecessary. Perform a clean boot. For Windows 9x or Windows 2000/XP,the simplest way is to boot to Safe Mode. If that doesn’t work, use your bootablerescue disk or disks.

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If the PC boots properly, turn your attention to the system that is not working andbegin troubleshooting there. In this chapter, since you are learning about electricityand power supplies, you will look more closely at how to troubleshoot thepower system.

Does the PC boot properly?

Is the screen blank?

Can you hear the drive or fanspinning, or see lights?

Start by troubleshootingthe motherboard.

Start by trouble-shooting video.

Eliminate the unnecessary:Perform a “clean boot.”

Can you hear a singlebeep during boot?

Respond tothe error message.

Start by troubleshootingthe power system.

Troubleshoot the systemthat is not working.

No Yes

NoYes

NoYes

NoYes

YesNo

Is there an errormessage on the screen?

Figure 4-17 Begin PC problem solving by asking the question, “Does the PC boot properly?”

APPLYING CONCEPTSYour friend Sharon calls to ask your help with a computer problem. Her system has been work-ing fine for over a year, but now strange things are happening. Sometimes the system powersdown while she is working for no apparent reason, and sometimes Windows locks up. As youread this section, look for clues as to what the problem might be. Also, as you read, think ofquestions to ask your friend that will help you.

Troubleshooting the Power System

First, let’s look at some general guidelines and some questions to ask when you havepower problems:

� Are there any burnt parts or odors? (Definitely not a good sign!)� Is everything connected and turned on? Are any cable connections loose? Is the

computer plugged in?


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� Are all the switches turned on? Computer? Monitor? Surge protector? Uninter-ruptible power supply? Separate circuit breaker? Is the wall outlet (or surge pro-tector) in working condition?

� If the fan is not running, turn off the computer, open the case, and check theconnections to the power supply. Are they secure? Are all cards securely seated?

For most of the newer ATX power supplies, a wire runs from the power switch onthe front of the ATX case to the motherboard. This wire must be connected to thepins on the motherboard and the switch turned on before power comes up. Checkthat the wire is connected correctly to the motherboard. Figure 4-18 shows the wire,which is labeled “REMOTE SW,” connected to pins on the motherboard labeled“PWR.SW.” If you are not sure of the correct connection on the motherboard, seethe motherboard documentation.

Figure 4-18 For an ATX power supply, the remote switch wire must be connected to the motherboardbefore power will come on

Then remove all nonessential expansion cards (modem, sound card, mouse) one ata time. This verifies that they are not drawing too much power and pulling the sys-tem down. It is possible that the expansion cards are all good but that the power sup-ply cannot provide enough current for all the add-on boards. Perhaps there are toomany cards and the computer is overheating. The temperature inside the case shouldnot exceed 113 degrees F (45 degrees C). You might need to add extra case fans,which is discussed later in the chapter.


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4

Remote SW



Vacuum the entire unit, especially the power supply’s fan vent, or use compressedair to blow out dust. Excessive dust insulates components and causes them to over-heat. Use an ESD-safe service vac that you can purchase from electronictools suppliers.

Remember from earlier in the chapter that strong magnetic or electrical interference can affecthow a power system functions. Sometimes an old monitor emits too much static and EMF (elec-tromagnetic force) and brings a whole system down. When you troubleshoot power problems,remember to check for sources of electrical or magnetic interference such as an old monitor orelectric fan sitting near the computer case.

Troubleshooting the Power Supply Itself

Problems with the PC’s power supply, the house current, or overheating can expressthemselves in the following ways:

� The PC sometimes halts during booting. After several tries, it boots successfully.� Error codes or beeps occur during booting, but they come and go.� The computer stops or hangs for no reason. Sometimes it might even reboot

itself.� Memory errors appear intermittently.� Data is written incorrectly to the hard drive.� The keyboard stops working at odd times.� The motherboard fails or is damaged.� The power supply overheats and becomes hot to the touch.

An overheated system can cause intermittent problems. Use com-pressed air or an antistatic vacuum to remove dust from the powersupply and the vents over the entire computer. Check that the powersupply fan and the fan over the CPU both work. A brownout (reduced current) of the house current or a faultypower supply might cause symptoms of electrical power problems. Ifyou suspect the house current could be low, check other devices that

are using the same circuit. A copy machine, laser printer, or other heavy equipmentmight be drawing too much power. Remove the other devices from the samehouse circuit.

A system with a standard power supply of about 250 watts that has multiple harddrives, multiple CD-ROM drives, and several expansion cards is most likely operat-ing above the rated capacity of the power supply, which can cause the system tounexpectedly reboot or give intermittent, otherwise unexplained errors. Upgrade thepower supply as needed to accommodate an overloaded power system.

If these suggestions don’t correct the problem, check the power supply by exchang-ing it for one you know is good. For an AT motherboard, be certain to follow theblack-to-black rule when attaching the power cords to the motherboard.

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✔✔ A+ EXAM TIPThe A+ Core exam expectsyou to recognize that agiven symptom is possiblypower or heat related.


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You can use a multimeter to measure the voltage output of a power supply anddetermine if it is supplying correct voltages, but know that a power supply that givescorrect voltages when you measure it might still be the source of problems, becausepower problems can be intermittent. See Appendix E, “Electricity and Multimeters,”to learn how to use a multimeter to measure voltage output from a power supply.

An electrical conditioner might solve the problem of intermittent errors caused bynoise in the power line to the PC. Try installing an electrical conditioner to monitorand condition voltage to the PC.

Troubleshooting the Power Supply Fan

An improperly working fan sometimes causes power supply problems. Usually justbefore a fan stops working, it hums or whines, especially when the PC is first turnedon. If this has just happened, replace the fan if you are trained to service the powersupply. If not, then replace the entire power supply, which is considered a fieldreplaceable unit (FRU) for a PC support technician. If you replace the power supplyor fan and the fan still does not work, the problem might not be the fan. A shortsomewhere else in the system drawing too much power might cause the problem.Don’t operate the PC if the fan does not work. Computers without cooling fans canquickly overheat and damage chips. To troubleshoot a nonfunctional fan, whichmight be a symptom of another problem and not a problem of the fan itself, followthese steps:

1. Turn off the power and remove all power cord connections to all components,including the connections to the motherboard, and all power cords to drives.Turn the power back on. If the fan works, the problem is with one of the sys-tems you disconnected, not with the power supply or its fan.

2. Turn off the power and reconnect the power cords to the drives. If the fancomes on, you can eliminate the drives as the problem. If the fan does not comeon, try one drive after another until you identify the drive with the short.

3. If the drives are not the problem, suspect the motherboard subsystem. With thepower off, reconnect all power cords to the drives.

4. Turn off the power and remove the power to the motherboard by disconnectingP1 or P8 and P9. Turn the power back on.

5. If the fan works, the problem is probably not the power supply but a short inone of the components powered by the power cords to the motherboard. Thepower to the motherboard also powers interface cards.

6. Remove all interface cards and reconnect plugs to the motherboard.

7. If the fan still works, the problem is one of the interface cards. If the fan doesnot work, the problem is the motherboard or something still connected to it.


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Power Problems with the Motherboard

The motherboard, like all other components inside the computer case, should begrounded to the chassis. Look for a metal screw that grounds the board to the com-puter case. However, a short might be the problem with the electrical system if somecomponent on the board makes improper contact with the chassis. This short canseriously damage the motherboard. Check for missing standoffs (small plastic ormetal spacers that hold the motherboard a short distance away from the chassis), theproblem that most often causes these improper connections.

Shorts in the circuits on the motherboard might also cause problems. Look fordamage on the bottom of the motherboard. These circuits are coated with plastic,and quite often damage is difficult to spot.

Frayed wires on cable connections can also cause shorts. Disconnect hard drivecables connected directly to the motherboard. Power up with P1 or P8 and P9connected but all cables disconnected from the motherboard. If the fan works, theproblem is with one of the systems you disconnected.

Never replace a damaged motherboard with a good one without first testing or replacing thepower supply. You don’t want to subject another good board to possible damage.

Overheating

If your computer hangs after it has been running for a while, you may have an over-heating problem. First, check whether there is airflow within the case. Open the caseand make sure the CPU and power supply fans are turning and that cables will notfall into the fans and prevent them from turning when you close the case. While youhave the case open, use an antistatic vacuum designed to be used around electronicequipment or a can of compressed air (both available at most computer supplystores) to blow dust off the motherboard and the CPU heat sink. Check the vents ofthe case, and clear any foreign material that may be blocking airflow.

After you close the case, leave your system off for a few hours. When you powerup the computer again, let it run for 10 minutes, go into CMOS setup, check the tem-perature readings, and reboot. Next, let your system run until it shuts down. Power itup again and check the temperature in setup again. A significant difference in thisreading and the first one you took after running the computer for 10 minutes indi-cates an overheating problem.

The problem might be caused by poor air circulation inside the case. The powersupply fan in ATX cases blows air out of the case, pulling outside air from the ventsin the front of the case across the processor to help keep it cool. Another exhaust fanis usually installed on the back of the case to help the power supply fan pull airthrough the case (see Figure 4-19). A third fan mounted on the processor is used tokeep air circulating near the processor to prevent hot air pockets from formingaround the processor. Air circulation problems can be caused by poor placement of

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vents and fans. Figure 4-20 shows a good arrangement of vents and fans for properairflow and a poor arrangement.

Figure 4-19 Install one exhaust fan on the rear of the case to help pull air through the case

Good arrangement for proper airflow

Power supplyProcessor

Driv

e ba

ys

Exhaustfan

Rearof case

Frontvents

Frontof case

airflow

Processor

Sidevents

Drivebays

Powersupply

Rear of case

Front of case

Poor arrangement for poor airflow

Figure 4-20 Vents and fans need to be arranged for best airflow

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For better ventilation, use a power supply that has vents on the bottom and frontof the power supply. Note in Figure 4-20 airflow is coming into the bottom of thepower supply because of these bottom vents. The power supply in Figure 4-19 hasvents only on the front and not on the bottom. Compare that to the power supply inFigure 4-21, which has vents on both the front and bottom.

Exhaust fan

Vents on the bottomof power supply

Figure 4-21 This power supply has vents on the bottom to provide better airflow inside the case

An intake fan on the front of the case might help pull air into the case. Intel rec-ommends you use a front intake fan for high-end systems, but AMD says a front fanis not necessary. Check with the processor manufacturer for specific instructions asto the placement of fans and what type of fan and heat sink to use. You will see someexamples of processor fans in the next chapter. Here are some general guidelines tohelp solve an overheating problem:

� Check your system that vents and at least one exhaust fan are in the right posi-tion so that air flows across the processor without expansion cards or ribboncables obstructing the flow.

� Check with the processor manufacturer Web site that you are using the rightsize processor fan and heat sink and the right thermal compound recommendedfor the specific processor.

� Check that your power supply has vents on the bottom.� Use tie wraps to secure cables and cords so that they don’t block airflow across

the processor.� An AGP video card generates a lot of heat. Leave the PCI slot next to the AGP

slot open to better ventilate the AGP card.

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� Install hard drives in large bays using a bay kit to make the small drive fit in thelarge bay, thus improving airflow around the drive.

� Monitor the temperature inside the case using a temperature sensor that soundsan alarm when a high temperature is reached or uses software to alert you of aproblem.

Be careful when trying to solve an overheating problem. Excessive heat itself maydamage the CPU and the motherboard, and the hard reboots necessary when yoursystem hangs may damage the hard drive. If you suspect damaged components, trysubstituting comparable components that you know are good.

APPLYING CONCEPTSBack to Sharon’s computer problem. Here are some questions that will help you identify thesource of the problem:

� Have you added new devices to your system? (These new devices might be drawing toomuch power from an overworked power supply.)

� Have you moved your computer recently? (It might be sitting beside a heat vent or electri-cal equipment.)

� Does the system power down or hang after you have been working for some time?

Intermittent problems like the one Sharon described are often heat related. If the systemonly hangs but does not power off, the problem might be caused by faulty memory or badsoftware, but because it actually powers down, you can assume the problem is related topower or heat.

If Sharon tells you that the system powers down after she’s been working for several hours,you can probably assume overheating. Check that first. If that’s not the problem, the nextthing to do is replace the power supply.

Energy Star Systems (The Green Star)

As you build or maintain a computer, one very important power consideration isenergy efficiency and conservation. Energy Star systems and peripherals have the U.S.Green Star, indicating that they satisfy certain energy-conserving standards of theU.S. Environmental Protection Agency (EPA). Devices that can carry the Green Starare computers, monitors, printers, copiers, and fax machines. Qualifying devices aredesigned to decrease overall electricity consumption in the United States, to protectand preserve natural resources. These standards, sometimes called the Green Stan-dards, generally mean that the computer or the device has a standby program thatswitches the device to sleep mode when it is not in use. During sleep mode, the devicemust use no more than 30 watts of power.

Energy Star Systems (The Green Star) 149

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Office equipment is among the fastest growing source of electricity consumption in industrial-ized nations. Much of this electricity is wasted, because people often leave computers and otherequipment on overnight. Because Energy Star devices go into sleep mode when they are unused,they create overall energy savings of about 50 percent.

Power Management Methods and Features

Computer systems use several different power management methods to conserveenergy. Some are listed below:

� Advanced Power Management (APM), championed by Intel and Microsoft� AT Attachment (ATA) for IDE drives� Display Power Management Signaling (DPMS) standards for monitors and

video cards� Advanced Configuration and Power Interface (ACPI), used with Windows 98

and Windows 2000/XP and supported by system BIOS

These energy-saving methods are designed to work incrementally, depending onhow long the PC is idle. The following sections discuss several specific features thatcan sometimes be enabled and adjusted using CMOS setup or using the OS. InCMOS setup, a feature might not be available, setup might include additional fea-tures, or a feature might be labeled differently from those described next. (How tochange these settings is covered in the next chapter.)

� Green timer on the motherboard. This sets the number of minutes of inactivitythat must pass before the CPU goes into sleep mode. You can enable or disablethe setting and select the number of minutes.

� Doze time. Doze time is the time that elapses before the system reduces 80 per-cent of its power consumption. Different systems accomplish this in differentways. For example, when one system enters doze mode, the system BIOS slowsdown the bus clock speed.

� Standby time. Standby time is the time that elapses before the system reduces92 percent of its power consumption. For example, a system might accomplishthis by changing the system speed from turbo to slow and suspending the videosignal.

� Suspend time. Suspend time is the time that elapses before the system reducesits power consumption by 99 percent. The way this reduction is accomplishedvaries. The CPU clock might be stopped and the video signal suspended. Afterentering suspend mode, the system needs warm-up time so that the CPU, moni-tor, and other components can reach full activity.

� Hard drive standby time. Hard drive standby time is the amount of time beforea hard drive shuts down.

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Figure 4-22 shows the Power Management Setup screen of the CMOS setup forAward BIOS for an ATX Pentium II motherboard.

ROM PCI/ISA BIOS (<<P2B>>)POWER MANAGEMENT SETUP

AWARD SOFTWARE, INC.

Power Management : User DefineVideo Off Option : Suspend -> OffVideo Off Method : DPMS OFF

** PM Timers **HDD Power Down : DisableSuspend Mode : Disable

** Power Up Control **PWR Button < 4 Secs : Soft OffPWR Up On Modem Act : EnabledAC PWR Loss Restart : DisabledWake On LAN : EnabledAutomatic Power Up : Disabled

: Select ItemPU/PD/+/- : Modify(Shift)F2 : Color

** Fan Monitor **Chasis Fan Speed : 3300RMPCPU Fan Speed : 3800RMPPower Fan Speed :

::

Ignore

** Thermal Monitor **CPU Temperature 50C/ 112FMB Temperature 25C/ 77F

** Voltage Monitor **VCORE Voltage : 3.3V+3.3V Voltage : 3.3V+5V Voltage : 5.0V+12V Voltage : 12.0V-12V Voltage : -12.0V-5V Voltage : -5.0V

ESC : QuitF1 : HelpF5 : Old ValuesF6 : Load BIOS DefaultsF7 : Load Setup Defaults

Figure 4-22 A Power Management Setup screen showing power management features

Using the Video options on the left of the screen, you can enable or disable powermanagement of the monitor. With power management enabled, you can controlEnergy Star features. The PM Timers feature controls doze, standby, and suspendmodes for the hard drive. The Power Up Control determines the way the system canbe controlled when it starts or when power to the computer is interrupted. The fea-tures on the right side of the screen monitor the power supply fan, CPU fan, optionalchassis fan, temperatures of the CPU and the motherboard (MB), and voltage outputto the CPU and motherboard.

Energy Star Monitors

Most computers and monitors sold today are Energy Star compliant, displaying thegreen Energy Star logo onscreen when the PC is booting. In order for a monitor’spower-saving feature to function, the video card or computer must also support thisfunction. Most monitors that follow the Energy Star standards adhere to the DisplayPower Management Signaling (DPMS) specifications developed by Video ElectronicsStandards Association (VESA), which allow for the video card and monitor to gointo sleep mode simultaneously.

To view and change energy settings of an Energy Star monitor using Windows XPor 2000, right-click the desktop and select Properties. The Display Properties dialog

Energy Star Systems (The Green Star) 151

A+CORE4.4

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box opens. Click the Screen Saver tab. If your monitor is Energy Star compliant, youwill see the Energy Star logo at the bottom. When you click the Power button, thePower Options Properties dialog box opens, and you can change your power options(see Figure 4-23). Your power options might differ depending on the power manage-ment features your BIOS supports.

Figure 4-23 Changing power options in Windows 2000

Problems might occur if system BIOS is turning off the monitor because of power managementsettings, and Windows 9x is also turning off the monitor. If the system hangs when you try toget the monitor going again, try disabling one or the other setting. It is best to use the OS orBIOS for power management, but not both.

CHAPTER SUMMARY

� Electrical voltage is a measure of the potential difference in an electrical system.

� Electrical current is measured in amps, and electrical resistance is measuredin ohms.




� Wattage is a measure of electrical power. Wattage is calculated by multiplyingvolts by amps in a system.

� Microcomputers require direct current (DC), which is converted from alternatingcurrent (AC) by the PC’s power supply inside the computer case.

� A PC power supply is actually a transformer and rectifier, rather than a supplier,of power.

� Materials used to make electrical components include conductors, insulators, andsemiconductors.

� A transistor is a gate or switch for an electrical signal, a capacitor holds an electri-cal charge, a diode allows electricity to flow in one direction, and a resistor limitselectrical current.

� To protect a computer system against ESD, use a ground bracelet, ground mat,and static shielding bags.

� Protect a computer system against EMI by covering expansion slots (which alsoreduces dust inside the case), by not placing the system close to or on the same cir-cuit as high-powered electrical equipment, and by using line conditioners.

� Devices that control the electricity to a computer include surge suppressors, lineconditioners, and UPSs.

� A surge suppressor protects a computer against damaging spikes inelectrical voltage.

� Line conditioners level the AC to reduce brownouts and spikes.

� A UPS provides enough power to perform an orderly shutdown during a blackout.

� There are two kinds of UPSs: the true UPS (called the inline UPS), and thestandby UPS.

� The inline UPS is more expensive, because it provides continuous power. Thestandby UPS must switch from one circuit to another when a blackout begins.

� Utility software at a remote computer or a computer connected to the UPSthrough a USB or serial cable can control and manage a smart UPS.

� Data line protectors are small surge suppressors designed to protect modems fromspikes on telephone lines.

� A form factor is a set of specifications for the size and configuration of hardwarecomponents such as cases, power supplies, and motherboards.

� The most common form factor today is ATX. There is an ATX variation calledMini-ATX. ATX superseded the earlier AT and Baby AT form factors.

� Other form factors include LPX and NLX, in which expansion cards are mountedon a riser card that plugs into the motherboard.

Chapter Summary 153

4



� Case types include desktop, low-profile or slimline desktops, minitower, midi-tower, full-size tower, and notebook. The most popular case type in use today isthe miditower.

� A faulty power supply can cause memory errors, data errors, system hangs, orreboots; it can damage a motherboard or other components.

� To reduce energy consumption, the U.S. Environmental Protection Agency hasestablished Energy Star standards for electronic devices.

� Devices that are Energy Star compliant go into sleep mode, in which they use lessthan 30 watts of power.

� PCs that are Energy Star compliant often have CMOS settings that affect theEnergy Star options available on the PC.

KEY TERMS

For explanations of key terms, see the Glossary near the end of the book.

active backplanealternating current (AC)ampere or amp (A)ATATXBaby ATbackplane systembrownoutbus risercapacitorclamping voltagecompact casedata line protectordiodedirect current (DC)Display Power Management Signaling

(DPMS)doze timeelectromagnetic interference (EMI)electrostatic discharge (ESD)Energy Star

field replaceable unit (FRU)FlexATXform factorfull ATGreen Standardsground bracelethard drive standby timeintelligent UPSline conditionerline-interactive UPSlow-profile caseLPXMicroATXMini-ATXMini-LPXNLXohm (��)P1 connectorP8 connectorP9 connectorpassive backplane

power conditionerrectifierresistorriser cardsleep modeslimline casesmart UPSsoft powersoft switchspikestandby timestatic electricitysurge protectorsurge suppressorsuspend timetower casetransformertransistoruninterruptible power supply (UPS)volt (V)watt (W)




REVIEWING THE BASICS

1. Volts are a measure of what characteristic of electricity?

2. What is the normal voltage of house electricity in the U.S.?

3. Hot wires in home wiring are normally colored ____ and ground wires in com-puters are normally colored _____.

4. What is the difference between a transformer and a rectifier? Which are foundin a PC power supply?

5. What are the five voltages produced by an ATX power supply?

6. What are the four voltages produced by an AT power supply?

7. When working inside a computer, why is it important to not stack boards ontop of each other?

8. Describe the purpose of the ground line in a house circuit. Show the electricalsymbol for ground.

9. What is the basic electronic building block of an integrated circuit?

10. Why is a power supply dangerous even after the power is disconnected?

11. What is the symbol for a diode?

12. What is a simple way to detect EMI?

13. What is an unintended, high-current, closed connection between two points in acircuit called?

14. Which form factors use a riser card on the edge of the motherboard?

15. List five types of computer case form factors. What is the most popular type ofform factor for PCs today?

16. List three advantages an ATX system has over a baby AT system.

17. List four computer symptoms that indicate a faulty power supply.

18. How much power can a device use in sleep mode if it complies with GreenStandards?

19. Name one thing that can be set in CMOS that pertains to power management.

20. How can you easily tell if a computer is designed to comply with GreenStandards?

21. Name two surge suppressor specifications.

22. What are the two main types of uninterruptible power supplies?

23. How does a smart UPS differ from one that is not smart?

Reviewing the Basics 155

4



24. If you are asked to identify the form factor of a motherboard, what are two cri-teria you can use to help you identify the board?

25. What are three motherboard form factors that can be used with a compact case?

THINKING CRITICALLY

1. How much power is consumed by a load drawing 15 A with 120 V across it?

2. You suspect that a power supply is faulty, but you use a multimeter to measureits voltage output and find it to be acceptable. Why is it still possible that thepower supply may be faulty?

3. Someone asks you for help with a computer that hangs at odd times. You turnit on and work for about 15 minutes, and then the computer freezes and pow-ers down. What do you do first?

a. Replace the surge protector.

b. Replace the power supply.

c. Turn the PC back on, go into CMOS setup, and check the temperaturereading.

d. Install an additional fan.

4. In Figure 4-24, which motherboard is an AT board? An ATX board?

✔✔ A+ EXAM TIPThe A+ Core exam expectsyou to identify motherboardform factors, ports, connec-tors, and other featuresusing rough drawings likethe ones in Figure 4-24.


Motherboard A Motherboard B

Figure 4-24 Motherboard form factor identification



PROJECT 4-1: Exploring Energy Star Features on a PC

Write down each power management and Energy Star feature that can be set throughCMOS on your home or lab computer.

PROJECT 4-2: Making Price and Value Comparisons

At your local computer vendor(s), compare the prices and ratings of two differentsurge suppressors. Write down your findings.

PROJECT 4-3: Finding PC Power Supply Facts

Remove the cover from your home or lab PC, and answer the following questions:

1. How many watts are supplied by your power supply? (The number is usuallyprinted on the label on the top of the power supply.)

2. How many cables are supplied by your power supply?

3. Where does each cable lead?

4. Does the back of the power supply have a switch that can be set for 220 volts(Europe) or 110 volts (U.S.)?

PROJECT 4-4: Building a Circuit to Turn On a Light

1. From the following components, build a circuit to turn on a light:

� An AC light bulb or LED (Note: An LED has polarity—it must be connectedwith the negative and positive terminals in the correct positions.)

� A double-A battery (Note: A 9-volt battery can burn out some bulbs.)

� A switch (A knife switch or even a DIP switch will work.)

� Three pieces of wire to connect the light, the switch, and the battery

Hands-on Projects 157

4

HANDS-ON PROJECTS



2. Add a second battery to the circuit, and record the results.

3. Add a resistor to the circuit, and record the results.

4. Place an extra wire in the middle of the circuit running from the battery to theswitch (thus making a short), and record the results.

PROJECT 4-5: Researching the Market for a UPS for Your Computer System

For a computer system you can access, determine how much wattage output a UPSshould have in the event of a total blackout, and estimate how long the UPS shouldsustain power. Research the market and report on the features and prices of astandby UPS and an inline UPS. Include the following information in your report:

� Wattage supported

� Length of time the power is sustained during total blackout

� Line-conditioning features

� AC backup present or not present for the inline UPS

� Surge suppressor present or not present

� Number of power outlets on the box, and other features

� Written guarantees

� Brand name, model, vendor, and price of the device

PROJECT 4-6: Detecting EMI

Use a small, inexpensive AM radio. Turn the dial to a low frequency, away from astation. Put the radio next to several electronic devices. List the devices in order, fromthe one producing the most static to the one producing the least static. Listen to thedevices when they are idle and in use.

PROJECT 4-7: Calculating Wattage Used by Your Drives

Fill in the following table, and then calculate the total wattage requirements of alldrives in your system. Look for a wattage rating printed somewhere on the device.




Component Wattage

Hard drive

Floppy drive

CD-ROM drive

DVD drive

Zip drive

Other drive

Total wattage requirements for all drives: _______________

PROJECT 4-8: Exploring Computer System Form Factors

You will need to open your computer case to answer these questions about yourcomputer system:

1. What type of case do you have?

2. What are the dimensions of your motherboard in inches?

3. What form factor does your motherboard use?

4. What is the power rating of your power supply?

PROJECT 4-9: Taking Apart a Computer and Putting It Back Together

A PC technician needs to be comfortable with taking apart a computer and putting itback together. To learn the most from this project, do it using more than one system.Be sure to use a ground bracelet as you work, and follow the other safety precautionsin the chapter. You’ll also need a Phillips-head screwdriver, a flat-head screwdriver,paper, and a pencil.

1. Put the computer on a table with plenty of room. Have a plastic bag or cupavailable to hold screws. When you reassemble the PC, you will need to insertthe same screws in the same holes. This is especially important with the harddrive, because screws that are too long can puncture the hard drive housing.

2. Print out all CMOS settings or save them to a floppy disk. Make a bootabledisk if you don’t already have one. Turn off the PC and unplug it.

3. To remove the cover of your PC:

� Unplug the monitor, mouse, and keyboard, and move them out of your way.


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� For a desktop case or tower case, locate and remove the screws on the backof the case. Look for the screws in each corner and one in the top (see Figure4-25). Be careful not to unscrew any screws besides these. The other screwsprobably are holding the power supply in place (see Figure 4-26).

� After you remove the cover screws, slide the cover forward and up toremove it from the case, as shown in Figure 4-27.

� For tower cases, the screws are also on the back. Look for screws in all fourcorners and down the sides (see Figure 4-27). Remove the screws and thenslide the cover back slightly before lifting it up to remove it. Some towercases have panels on either side of the case, held in place with screws on theback of the case. Remove the screws and slide each panel toward the rear,then lift it off the case.

Figure 4-25 Locate the screws that hold the cover in place




Power supplymounting screws

Rear view

Figure 4-26 Power supply mounting screws

First, removethe screwsholding thecover in place

Then carefullypull the covertoward theback

Removing a standard case cover

Removing a tower case cover

Remove screws Pull cover back, then up, to remove

Figure 4-27 Removing the cover

4. Draw a diagram of all cable connections, DIP switch settings, and jumper set-tings. You might need the cable connection diagram to help you reassemble.You will not change any DIP switch settings or jumper settings in this project,but accidents do happen. Be prepared. If you like, use a felt-tip marker to makea mark across components, to indicate a cable connection, board placement,


4



motherboard orientation, speaker connection, brackets, and so on, so that youcan simply line up the marks when you reassemble.

5. Identify the following major components. (Drawings in this and previous chap-ters should help.)

� Power supply

� Floppy disk drive

� Hard drive

� Motherboard

6. Before removing any cables, note that each cable has a color or stripe down oneside. This edge color marks this side of the cable as pin 1. Look on the board ordrive that the cable is attached to. You should see that pin 1 or pin 2 is clearlymarked. (See Figure 4-28.)

1 2

19 20 33 34

21 1 12 2

2019 3433

1 2

19 20 33 34

21 1 12 2

2019 3433

Pin 1 is shown by square solderpads on the reverse side of the circuit board

Pin 1 is shownby a stencil onthe circuit board

Figure 4-28 How to find pin 1 on an expansion card

7. Verify that the edge color is aligned with pin 1. Look at the cable used to con-nect drive A to the floppy drive controller card. There is a twist in the cable.This twist reverses the leads in the cable, causing the addresses for this cable tobe different from the addresses for the cable that doesn’t have the twist. Theconnector with the twist is attached to drive A (see Figure 4-29). Remove thecables to the floppy drives and the hard drives. Remove the power supply cordsfrom the drives.




Controller Cable twist

Drive B Drive A

Reverses original twist

Drive BDrive A Tapedrive

Typical PC floppy cable

Controller

Figure 4-29 Twist in cable identifies drive A

8. Remove the expansion cards, following these procedures. (If you are workingwith a tower case, you can lay it on its side so the motherboard is on thebottom.)

a. Remove the cables from the card. There is no need to remove the otherend of the cable from its component (floppy disk drive, hard drive, orCD-ROM drive). Lay the cable over the top of the component or case.

b. Remove the screw holding the board to the case.

c. Grasp the board with both hands and remove it by lifting straight up androcking the board from end to end (not side to side). Rocking the boardfrom side to side might spread the slot opening and weaken the connection.

d. As you remove cards, don’t put your fingers on the edge connectors ortouch a chip, and don’t stack the cards on top of one another.

9. Examine the board connector for the cable. Can you identify pin 1? Lay theboard aside on a flat surface.

10. Remove the floppy drive next. Some drives have one or two screws on each sideof the drive attaching the drive to the drive bay. After you remove the screws,the drive usually slides to the front and out of the case. Sometimes there is acatch underneath the drive that you must lift up as you slide the drive forward.Be careful not to remove screws that hold the circuit card on top of the drive tothe drive housing. The whole unit should stay intact.

11. Remove the hard drive next. Look for the screws that hold the drive to the bay.Be careful to remove only these screws, not the screws that hold the drivetogether. Handle the drive with care.


4



12. You might need to remove the power supply before exposing the motherboard.Unplug the power supply lines to the motherboard. An ATX power supply onlyhas a single power line, but for an AT power supply, carefully note which lineis labeled P8 and which is labeled P9. You will want to be certain that youdon’t switch these two lines when reconnecting them, since this would cause thewrong voltage to flow in the circuits on the motherboard and could destroy theboard. Fortunately, most connections today only allow you to place the lines inthe correct order, which is always black leads on P8 next to black leads on P9.Remember, “black to black.” Look for screws that attach the power supply tothe computer case, as shown in Figure 4-30. Be careful not to remove anyscrews that hold the power supply housing together. You do not want to takethe housing apart. After you have removed the screws, the power supply stillmight not be free. Sometimes it is attached to the case on the underside byrecessed slots. Turn the case over and look on the bottom for these slots. If theyare present, determine in which direction you need to slide the power supply tofree it from the case.

Figure 4-30 Removing the power supply mounting screws

13. The motherboard is the last thing to be removed. It probably has spacers keep-ing it from resting directly on the bottom of the computer case. Carefully popoff these spacers and/or remove the three or four screws that hold the board tothe case.

14. You are now ready to reassemble. Reverse the preceding disassemblingactivities. Place each card in its slot (it doesn’t have to be the same slot, just thesame bus) and replace the screw. Don’t place the video card near the powersupply.

15. Replace the cables, being sure to align the colored edge with pin 1. (In somecases it might work better to connect the cable to the card before you put thecard in the expansion slot.)




16. Plug in the keyboard, monitor, and mouse.

17. In a classroom environment, have the instructor check your work before youpower up.

18. Turn on the power and check that the PC is working properly before youreplace the cover. Don’t touch the inside of the case while the power is on.

19. If all is well, turn off the PC and replace the cover and its screws. If the PC doesnot work, don’t panic! Just turn off the power and go back and check eachcable connection and each expansion card. You probably have not solidlyseated a card in the slot. After you have double-checked, try again.


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