1. A+ Guide to Hardware, 4e
Chapter 3
Form Factors and Power Supplies

2. 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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3. 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:
– Measurements of electricity
– How electricity is delivered
– Protecting a PC from electrical damage
– Changing a defective power supply
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4. 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:
– 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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5. 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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6. 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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7. 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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8. 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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9. 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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10. Figure 3-13 Tower and desktop cases
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11. Measures and Properties of Electricity
• Successful PC technicians:
– 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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12. Table 3-2 Measures of electricity
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13. 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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14. Figure 3-15 A transformer keeps power constant but
changes the ratio of current to voltage
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15. Hot, Neutral, and Ground
• Completing a circuit:
– 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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16. 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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17. Figure 3-18 Use a receptacle tester to verify that hot,
neutral, and ground are wired correctly
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18. 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
– 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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19. Figure 3-19 Symbols for some electronic components and for ground
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20. 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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21. Figure 3-20 Capacitors on a motherboard or other circuit
board often have embedded crossed lines on top
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22. 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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23. 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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24. 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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25. 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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26. Surge Suppressors
• Also called a surge protector
• Protects equipment from sudden changes in power
– Works by absorbing and/or blocking the surge
• Recommended features:
– 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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27. Figure 3-21 This surge suppressor has six electrical outlets,
two phone jacks, and a power protection light
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28. 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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29. 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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30. 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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31. 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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32. Figure 3-24 A power management BIOS setup screen
showing power-management features
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33. 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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34. Figure 3-25 Changing power options in Windows XP
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35. Troubleshooting the Electrical System
• Problems can occur before or after boot
• Problems can be consistent or inconsistent
• Possible symptoms of an electrical problem:
– 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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36. 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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37. 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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38. 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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39. Problems that Come and Go
• Intermittent symptoms indicating a post-boot
problem
– 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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40. 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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41. 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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42. 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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43. 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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44. Problems with Overheating
• 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:
– 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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45. Figure 3-27 Install one exhaust fan on the rear of the case
to help pull air through the case
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46. 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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47. 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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48. 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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