A+ Guide to Hardware, 4e
Chapter 3
Form Factors and Power Supplies
Objectives
• Learn about different form factors and computer
cases
• Learn how electricity is measured
• Learn how to protect your computer system against
damaging changes in electrical power
• Learn about Energy Star specifications
• Learn how to troubleshoot electrical problems
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Introduction
• Power supply: passes power to PC components
• Elements driving type of power supply used in a PC:
– The motherboard
– The form factor of the computer case
• Energy Star devices: designed to save energy
• Electricity topics covered:
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Measurements of electricity
How electricity is delivered
Protecting a PC from electrical damage
Changing a defective power supply
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Computer Case, Motherboard, and
Power Supply Form Factors
• Form factor
– Specifies size, shape, features of a hardware device
• Form factor for motherboard is chosen first
– Same form factor is used for case and power supply
• Using the same form factor assures you that:
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The motherboard fits the case
The powers supply cords provide proper voltage
Holes in the motherboard align with holes in the case
Holes in the case align with ports off the motherboard
Wires on the case match connections on motherboard
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Types of Form Factors
• AT (Advanced Technology) form factor
– Specified motherboard dimensions of 12” x 13.8”
– Utilized by IBM AT PC in the 1980s
• Baby AT form factor
– Specified motherboard dimensions of 13” x 8.7”
– Industry standard form factor from 1993 to 1997
• ATX form factor
– Specified motherboard dimensions of 12” x 9.6”
– Open specification that is most commonly used today
– Includes all AT voltages plus a +3.3-volt circuit
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Figure 3-4 The CPU on an ATX motherboard sits opposite the
expansion slots and does not block the room needed for long
expansion cards
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Types of Form Factors (continued)
• MicroATX form factor
– Reduces number of I/O slots on the motherboard
• BTX (Balanced Technology Extended) form factor
– Focuses on reducing heat and supporting motherboard
• LPX and Mini-LPX form factors
– Designed for low-end PC motherboards
• NLX form factor
– Developed to improve the LPX form factor
• Backplane Systems (Active and Passive)
– Use boards with slots, but little or no circuitry
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Figure 3-8 Improved airflow in a BTX case and
motherboard makes it unnecessary to have a fan
on top of the processor
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Types of Cases
• Computer case (chassis)
– Houses power supply, motherboard, cards, drives
– Panel switches/lights are used to control/monitor PC
• Desktop cases
– Motherboard on the bottom, power supply to the rear
• Tower cases
– Are up to 2 feet high and can contain several drives
• Notebook cases
– Used for all portables and have desktop components
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Figure 3-13 Tower and desktop cases
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Measures and Properties of Electricity
• Successful PC technicians:
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Understand electricity
Know how to use electricity
Know how to measure electricity
Can protect computer equipment from electricity
• Units used to measure characteristics of electricity
– Volt, amp, ohm, and watt
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Table 3-2 Measures of electricity
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AC and DC
• Alternating current (AC)
– Oscillatory current driven by an alternating voltage
– Example: house current oscillates at 60 Hz
• Direct current (DC)
– Single direction current driven by constant voltage
– Required by computer in small amounts, such as 5 V
• Rectifier: converts AC to DC
• Transformer: changes ratio of current to voltage
• Power supply acts as a transformer and rectifier
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Figure 3-15 A transformer keeps power constant but
changes the ratio of current to voltage
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Hot, Neutral, and Ground
• Completing a circuit:
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AC travels from power station to house on a hot line
AC travels from panel to device using black (hot) wire
AC flows out of device circuit in a white (neutral) wire
AC returns to power station on a neutral line
• Short circuit: failure due to excess flow of electricity
– Fuses protect circuits by melting wire (breaking circuit)
– Grounded neutral lines pass detoured AC to earth
• Lines in three-prong plugs: hot, neutral, and ground
– Verify wiring of outlet for plug using a receptacle tester
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Figure 3-16 Normally, electricity flows from hot to neutral to make
a closed circuit in the controlled environment of an electrical
device such as a lamp
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Figure 3-18 Use a receptacle tester to verify that hot,
neutral, and ground are wired correctly
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Some Common Electric Components
• Materials used to make components:
– Conductors: weakly resist flow of current; e.g., copper
– Insulators: highly resist flow of current; e.g., ceramics
– Semiconductors: allow flow if charged; e.g., silicon
• Transistor
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Used to switch current on (1) and off (0)
Also used to amplify current
Made of three layers of semiconductor material
Charge applied to center layer controls switching
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Figure 3-19 Symbols for some electronic components and for ground
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Some Common Electric Components
(continued)
• Capacitor
– Holds electrical charge for a period of time
– Used to create even flow of current in a PC
• Diode
– Allows electricity to flow in one direction only
– Used to rectify current (convert AC to DC)
• Resistor
– Controls the amount of current flowing through device
– Degree of resistance is measured in ohms
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Figure 3-20 Capacitors on a motherboard or other circuit
board often have embedded crossed lines on top
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Protecting Your Computer System
• Electrical threats to a computer system:
– Static electricity
– Electromagnetic interference
– Power surges
• Objectives in this section:
– Understand nature of each threat
– Learn how to protect your system from these threats
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Static Electricity
• Static electricity (electrostatic discharge or ESD)
– Due to charge difference between user and device
– Touching device causes discharge, damaging device
• ESD is particularly severe in dry and cold climates
• How to protect system from ESD:
– Use ground bracelet or ESD gloves
– Touch computer case before touching components
• Safety rule: unplug power cord before working in case
– Residual power in plugged device can cause damage
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EMI (Electromagnetic Interference)
• Caused by magnetic fields generated by current flow
• RFI (radio frequency interference):
– EMI in radio frequency range affecting reception
• The crosstalk problem
– Data in cables crossing EM fields gets corrupted
– Control crosstalk by shielding cables and power supply
• Use a tuned-down AM radio to detect EMI
• Other ways to protect a device from EMI:
– Use line conditioners to filter out electrical noise
– Move the PC to a new location
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Surge Protection and Battery Backup
• Storms and uneven AC flow cause power surges
• Prevent power surges by installing an AC filter
• Types of devices used to manage power surges:
– Surge suppressors
– Power conditioners
– Uninterruptible power supplies (UPSs)
• Use devices with UL (Underwriters Laboratory) logo
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Surge Suppressors
• Also called a surge protector
• Protects equipment from sudden changes in power
– Works by absorbing and/or blocking the surge
• Recommended features:
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Joules rating that is greater than 600 joules
Protection activated in less than 2 nanoseconds
Warranty for connected equipment and UL seal
Light indicating that surge protection is working
Data line protector for telephone line to modem
Let-through voltage rating and line noise filtering
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Figure 3-21 This surge suppressor has six electrical outlets,
two phone jacks, and a power protection light
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Power Conditioners
• Sometimes called line conditioners
• Functions:
– Protect against spikes or swells (voltage surges)
– Raise voltage during brownouts (voltage sags)
• Load supported measured in watts or volt-amps (VA)
• Determining the VA needed to support your system:
– Multiply the amperage of each component by 120 V
– Add up the VA for each component
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Uninterruptible Power Supply
• UPS offers three benefits:
– Conditions line to account for brownouts and spikes
– Provides power backup when AC fails (blackout)
– Provides protection against very high spikes
• Designs: standby, inline, and line-interactive
• Smart (intelligent) UPS: controlled with software
• What to consider when buying a UPS:
– UPS rating should exceed VA load by at least 25 %
– Degree of line conditioning
– Warranties, guarantees, and service policies
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Energy Star Systems (The Green Star)
• Energy Star systems have the U.S. Green Star
– Indicates device meets energy conserving standards
– Devices: computers, monitors, printers, copiers, faxes
• Goals of Energy Star (a.k.a. Green) standards:
– Reduce overall electricity consumption
– Protect and preserve natural resources
• How computer components meet standards
– Uses standby program for switching to sleep mode
– No more than 30 watts used during sleep mode
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Power-Management Methods and
Features
• Methods used to meet Energy Star standards:
– Advanced Configuration and Power Interface (ACPI)
• Standard used by most desktops and notebooks
• Comprises four power-saving modes: S1 - S4
• Some features controlled by BIOS, others by Windows
– Advanced Power Management (APM) specification
– AT Attachment (ATA) for various drives
– Display Power Management Signaling (DPMS)
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Figure 3-24 A power management BIOS setup screen
showing power-management features
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Energy Star Monitors
• Display Power Management Signaling (DPMS)
– Specifications applying to video card and monitor
– Allow both devices to simultaneously enter sleep mode
• Accessing energy settings in Windows 2000/XP
– Right-click the desktop and select Properties
• The Display Properties dialog box opens
– Click the Screen Saver tab
• If monitor is Energy Star–compliant, logo is at bottom
– Click Power button to open Power Options Properties
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Figure 3-25 Changing power options in Windows XP
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Troubleshooting the Electrical System
• Problems can occur before or after boot
• Problems can be consistent or inconsistent
• Possible symptoms of an electrical problem:
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The PC appears “dead”
The PC sometimes halts during booting
Error codes or beeps occur during booting
You smell burnt parts or odors
• Check the simple things first
– Example: determine whether all switches are on
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Problems with External Power
• Brownout (reduced current) may create issues
– Check out other devices using the same circuit
– Remove other devices to see if voltage increases
• Dealing with intermittent errors caused by noise:
– Use a line monitor to monitor and condition voltage
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Problems with Loose Internal
Connections
• Can cause a system to appear dead or reboot itself
• Troubleshooting tasks:
– Remove the cover of the case
– Check all power connections
• Check cables linking power supply to motherboard
• Check cables linking power supply to drives
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Figure 3-26 For an ATX or BTX power supply, the
remote switch wire must be connected to the
motherboard before power will come on
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Problems that Come and Go
• Intermittent symptoms indicating a post-boot problem
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The computer stops or hangs or reboots for no reason
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
Power supply overheats and becomes hot to the touch
The power supply fan becomes very noisy or stops
• Intermittent problems are often difficult to solve
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Problems with an Inadequate Power
Supply
• Power supply may not meet needs of new devices
• Testing for an adequate power supply
– Make all devices in the system work at the same time
– Example: copy files from new drive to old drive
• Simple solution: upgrade to a higher power supply
• Calculating total wattage needed by system
– Multiply volts in circuit by amps required for device
– Add all products to determine total wattage
• Power supply range: 200 watts to 600 watts
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Problems with the Power Supply,
Boards, or Drives
• Issues:
– Inadequate or faulty power supply
– Components drawing power might be bad
• Problems caused:
– System hangs or gives intermittent errors
– System reboots or does not boot at all
• Actions to take:
– Isolate and remove any faulty expansion cards
– Upgrade or switch the power supply
– Test voltage output of power supply with a multimeter
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Problems with the Power Supply Fan
• Defective fans usually hum before they stop working
• Response to diagnosis of defective fan
– Replace fan or the entire power supply
• If replacement does not work, suspect another short
• Do not operate a PC if the fan does not work
– Computers will overheat, damaging circuit boards
• Indirect sources of fan problems:
– Shorts in drives, motherboard, or expansion cards
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Power Problems with the Motherboard
• Bad contact between board component and chassis
– Short can seriously damage the motherboard
– Check for missing or extra standoffs (spacers)
• Shorts in the circuit on the motherboard
– Look for damage to the bottom of the motherboard
– Look for burned-out capacitors
• Frayed wires on connections can also cause shorts
– Test hard drive cables connected to motherboard
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Problems with Overheating
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Causes intermittent problems
May also cause the system to reboot or not boot
Temperature in a case should not exceed 100° F
Some possible solutions:
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Remove dust from power supply, vents, heat sink
Secure cables and cords with tie wraps
Install another exhaust fan on the rear of the case
Install a fan in expansion slot next to video card
Replace component that is damaged
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Figure 3-27 Install one exhaust fan on the rear of the case
to help pull air through the case
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Replacing the Power Supply
• The power supply is a field replaceable unit (FRU)
• Criteria for replacement power supply to meet:
– Uses the correct form factor
– Adequately rated for power in watts
– Has all power connectors needed by your system
• Before replacing power supply, test new device
– Connect components to new power supply
– Turn on PC and observe whether problem is solved
– If problem is solved, perform replacement procedure
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Summary
• Form factor: specifies size, shape, features of device
• Motherboard, power supply, and case share the same
form factor, such as ATX
• Three types of cases: desktop, tower, and notebook
• Quantities that characterize electricity: voltage,
current, resistance, and power
• Current flows from hot wires to neutral wires; excess
current escapes through grounds
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Summary (continued)
• AC supplied by power station is transformed and
rectified before flowing into the PC
• Major components in a circuit board: transistor,
capacitor, diode, resistor
• Electrical threats: ESD, EMI, uneven current flow,
sudden power surges (or spikes)
• Energy Star standards promote energy conservation
• PCs comply with Energy Star standards by enabling
devices to enter into a low power sleep mode
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