A Guide to Hardware, 4e

1
A Guide to Hardware, 4e

• Chapter 3
• Form Factors and Power Supplies

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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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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 3-13 Tower and desktop cases
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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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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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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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Figure 3-18 Use a receptacle tester to verify
that hot, neutral, and ground are wired correctly
12
Figure 3-19 Symbols for some electronic
components and for ground
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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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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 3-25 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
• 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
• 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

• 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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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