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Chapter 4 Form Factors & Power Supplies
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Chapter 4 Form Factors & Power Supplies


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  • 1. A+ Guide to Managing and Maintaining your PC, 6e Chapter 4 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
  • 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
  • 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
  • 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
  • 6. Figure 4-4 The CPU on an ATX motherboard sits opposite the expansion slots and does not block the room needed for long expansion cards
  • 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
  • 8. Figure 4-8 Improved airflow in a BTX case and motherboard makes it unnecessary to have a fan on top of the processor
  • 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
  • 10. Figure 4-13 Tower and desktop cases
  • 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
  • 12. Table 4-2 Measures of electricity
  • 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
  • 14. Figure 4-15 A transformer keeps power constant but changes the ratio of current to voltage
  • 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
  • 16. Figure 4-16 Normally, electricity flows from hot to neutral to make a closed circuit in the controlled environment of an electrical device such as a lamp
  • 17. Figure 4-18 Use a receptacle tester to verify that hot, neutral, and ground are wired correctly
  • 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
  • 19. Figure 4-19 Symbols for some electronic components and for ground
  • 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
  • 21. Figure 4-20 Capacitors on a motherboard or other circuit board often have embedded crossed lines on top
  • 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
  • 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
  • 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
  • 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
  • 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
  • 27. Figure 4-21 This surge suppressor has six electrical outlets, two phone jacks, and a power protection light
  • 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
  • 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
  • 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
  • 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)
  • 32. Figure 4-24 A power management BIOS setup screen showing power-management features
  • 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
  • 34. Figure 4-25 Changing power options in Windows XP
  • 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
  • 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
  • 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
  • 38. Figure 4-26 For an ATX or BTX power supply, the remote switch wire must be connected to the motherboard before power will come on
  • 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
  • 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
  • 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
  • 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
  • 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
  • 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
  • 45. Figure 4-27 Install one exhaust fan on the rear of the case to help pull air through the case
  • 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
  • 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
  • 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