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📄 Contents

  1. Foundation Topics
  2. Exam Preparation Tasks
This chapter is from the book

Exam Preparation Tasks

Review All the Key Topics

Review the most important topics in the chapter, noted with the key topics icon in the outer margin of the page. Table 4-4 lists a reference of these key topics and the page numbers on which each is found.


Table 4-4. Key Topics for Chapter 4

Key Topic Element


Page Number


Power supply converts AC to DC



A typical ATX power supply


Figure 4-1

Power supply ratings



Determining the wattage rating needed for a replacement power supply



Voltage ranges supported by power supplies


Figure 4-4

20-pin, 24-pin, and ATX12V and AUX connectors


Figure 4-5

Power supply pinouts


Figure 4-6

Power supply connectors for peripheral and modern motherboards



Steps for removing the power supply



Symptoms of an overloaded power supply



Fan failure indicators



Causes for a “dead” system



Diagnosing power supply problems



Causes of overheating



Multimeter test procedures


Table 4-3

Acceptable voltage levels



Power supply hazards



Surge suppressors



Battery backup units



Power conditioning units



Cooling motherboard chipsets


Complete the Tables and Lists from Memory

Print a copy of Appendix A, “Memory Tables,” (found on the CD), or at least the section for this chapter, and complete the tables and lists from memory. Appendix B, “Memory Tables Answer Key,” also on the CD, includes completed tables and lists to check your work.

Define Key Terms

Define the following key terms from this chapter, and check your answers in the glossary.

power supply, AC, DC, multimeter, surge suppressor, battery backup, thermal compound

Complete Hands-On Lab

Complete the hands-on labs, and then see the answers and explanations at the end of the chapter.

Lab 4-1: Check Power Supply Voltages

Scenario: You are a technician working at a PC repair bench. You need to determine whether the power supply is supplying correct voltage to the motherboard without opening the system.

Procedure: Start the system, open the BIOS setup program, and open the dialog that displays power levels (System Health, PC Health, System Monitor are typical names). Check the voltage levels listed against those listed in Table 4-3.

Lab 4-2: Check for Airflow Problems Inside the System

Scenario: You are a technician working at a PC repair bench. You need to determine whether the cable layout inside the system may be causing overheating.

Procedure: Use the procedure for Lab 4-1 to check system temperature after running the system for about a half-hour. Record the current temperature. Shut down the system, unplug it from AC power, and open the system. Compare the interior of the system to Figures 4-11 and 4-12. If the system resembles Figure 4-11, the system needs better cable organization.

Answer Review Questions

Answer these review questions and then see the answers and explanations at the end of the chapter.

  1. Which of the following would you use to keep the power supply working properly? (Choose two.)
    1. Surge protector
    2. Extra power supply
    3. UPS units
    4. Multimeter
  2. Power supplies are rated using which of the following units?
    1. Amps
    2. Volts
    3. Watts
    4. Output
  3. Newer tower-case computers’ power supplies typically have which of the following power output ratings?
    1. 300 watts
    2. 400 watts
    3. 250 watts
    4. 500 watts or higher
  4. Most power supplies in use today are designed to handle which two voltage ranges? (Choose two.)
    1. 115
    2. 300
    3. 230
    4. 450
  5. Which of the following are causes of power supply overheating?
    1. Overloading the power supply.
    2. Fan failure.
    3. Dirt or dust.
    4. All of these options are correct.
  6. How many pins are used for the main power connection by recent ATX/BTX motherboards with ATX12V 2.2 power supplies?
    1. 24
    2. 48
    3. 32
    4. 16
  7. What is the four-pin square power connector on the motherboard used for?
    1. Extra power to PCIe slots
    2. 5-volt power for fans
    3. 12-volt power for processors
    4. 12-volt power for fans
  8. What is the six-pin power lead on the power supply used for?
    1. Extra power to PCIe x16 cards
    2. Extra power for PCI cards
    3. Power for case fans
    4. Power supply diagnostics
  9. Which of the following steps would you use to remove a power supply?
    1. Shut down the computer. If the power supply has an on/off switch, turn it off as well.
    2. Disconnect the AC power cord from the computer.
    3. Disconnect power connections from the motherboard, hard drives, and optical drives.
    4. All of these options are correct.
  10. To avoid power supply hazards you must never do which of the following? (Choose two.)
    1. Disassemble the power supply.
    2. Put metal tools through the openings.
    3. Switch the voltage to 220.
    4. Put a smaller power supply in the computer.
  11. Which device provides emergency power to a computer in case of a complete power failure?
    1. UTP
    2. UPS
    3. Power strip
    4. Surge protector
  12. What is the minimum time recommendation for a UPS to supply power for an individual workstation?.
    1. 30 minutes
    2. 45 minutes
    3. 1 hour
    4. 15 minutes
  13. Which of the following correctly describe an SPS? (Choose all that apply.)
    1. An SPS is on all the time.
    2. The battery on an SPS is only used when the AC power fails.
    3. A momentary gap in power occurs between loss of AC power and when the SPS comes online.
    4. An SPS is far less expensive than a UPS.
  14. When a system is dead and gives no signs of life when you turn on the computer, which of the following might be the cause? (Choose all that apply.)
    1. Defects in AC power to the system
    2. Power supply failure or misconfiguration
    3. Temporary short circuits in internal or external components
    4. Power button or other component failure
  15. Processors and other components use a finned metal device to help with cooling. What is this device called? (Choose two.)
    1. Passive heat sink
    2. Thermal compound
    3. Active heat sink
    4. Chassis heat sink
  16. What is the purpose of thermal compound?
    1. Provides the best possible thermal transfer between a component and its heat sink
    2. Provides the best possible thermal transfer between a component’s heat sink and its fan
    3. To negate the effects of thermal contraction and expansion in adapter cards
    4. Provides the best possible thermal transfer between the northbridge and its fan

Answers to Hands-On Lab

Lab 4-1: Check Power Supply Voltages

Answer: If the voltage levels are within limits, the power supply is healthy. If any of the voltage levels are out of range, the power supply should be replaced with a power supply of the same or higher wattage rating.

Lab 4-2: Check for Airflow Problems Inside the System

Answer: Use cable ties and reroute long cables between the drive bays at the back wall of the system or along the edge of the motherboard to reduce snarls and improve airflow. After reassembling the system, reconnecting it to AC power, and booting the system to the BIOS setup program, recheck system temperature after running the system for a half-hour. If the temperature is lower, you have improved airflow inside the system. Even if the system temperature remains the same, you have made it easier to work inside the system in the future.

Answers and Explanations to Review Questions

  1. A, C. To keep your power supply up and running and to help prevent damage from power surges, you should use a surge protector. The UPS will supply power for a short period of time to the computer system in case of total power outage.
  2. C. Power supplies are rated in watts, and the more watts a power supply provides, the more devices it can safely power.
  3. D. Most newer tower computers have 500 watt or larger power supplies in them because of the greater number of drives and expansion cards that are available now.
  4. A, C. Standard North American power is 115 volts, and power in most parts of Europe and Asia is 230 volts. Some power supplies have a slider on the back to switch between the two voltages.
  5. D. All of the listed reasons can cause damage to the power supply as well as overheating your computer.
  6. A. Most of the newer power supplies in use today have 24 pins. Older motherboards have a 20-pin connection.
  7. C. This connector is the ATX12V connector, which provides 12V power dedicated to the processor (a voltage regulator on the motherboard reduces 12V to the actual power required by the processor).
  8. A. The six-pin (or 6+2 pin) power supply lead provides additional power needed by high-performance PCIe x16 cards, such as those used for SLI or for CrossFire X multi-GPU installations.
  9. D. All of the listed answers are correct. You must disconnect from the wall first; then once inside the computer unhook the connection to the motherboard, drives, and other devices.
  10. A, B. The capacitors inside the power supply retain potentially fatal voltage levels. To prevent shock you should not disassemble power supplies or stick in a metal object such as a screwdriver.
  11. B. A UPS (uninterruptible power supply) will keep a standard desktop up and running in case of a complete power outage.
  12. D. UPSs are designed to supply power to a computer long enough for you to complete a formal shutdown.
  13. A, C, D. When an SPS is used there is a momentary gap, usually about 1ms or less, between when the power goes off and when the SPS starts supplying power. SPSs are also less expensive and are not used at all times.
  14. A, B, C, D. When turning on a system that shows no signs of life you must consider all of these as potential problems.
  15. A, C. All processors require a heat sink. A heat sink is a finned metal device that radiates heat away from the processor. An active heat sink (a heat sink with a fan) is required for adequate processor cooling on current systems. Some older systems used a specially designed duct to direct airflow over a processor with a passive heat sink (a heat sink without a fan). Most motherboards’ northbridges use passive heat sinks or heat pipes.
  16. A. Thermal compound (also known as thermal transfer material, thermal grease, or phase change material) provides for the best possible thermal transfer between a component (for example a CPU) and its heat sink. This prevents CPU damage. The fan and adapter cards should not have thermal compound applied to them.

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