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PC Repair and Maintenance: In-depth Look at Power Supply

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Scott Mueller shows you how to test, remove, and install a power supply. Includes power supply specifications and troubleshooting tips.

Student Learning Objectives

In this chapter, you will

  • Learn about the various power supply form factors used in PCs today

  • Study the connectors used with power supplies, including a connector used by one major manufacturer that could destroy your motherboard if you're not careful

  • Learn how to understand power supply ratings and specifications

  • Troubleshoot power supply problems, which are oft-overlooked culprits when tracking pesky system problems

  • Learn how to test, remove, and install a power supply

  • Study power protection systems, surge suppressors, and uninterruptible power supplies

Terms to Study

The following terms are just a few of the terms used in this chapter. Watch for these terms as you read. Definitions for each can be found in the UPGRADE.HLP file located on the CD-ROM or in Appendix A, "Glossary." Reviewing these terms before and after you read this chapter will deepen your understanding of this chapter.


You will get more from this chapter if you spend a few minutes thinking about each term before you start reading. See how many you can define before you read the chapter. After you have finished the chapter, look at the list of terms and see whether you were right.

  1. Step Power good signalStep
  2. Step DCStep
  3. Step ACPIStep
  4. Step BrownoutStep
  5. Step Power supplyStep
  6. Step Back probingStep
  7. Step Surge protectorStep
  8. Step Form factorStep
  9. Step POSTStep
  10. Step UPSStep
  11. Step full towerStep
  12. Step Mini-towerStep

Considering the Importance of the Power Supply

The power supply is not only one of the most important parts in a PC, but it is unfortunately also the most overlooked. In the words of a famous comedian, the power supply gets no respect! People spend hours discussing their processor speeds, memory capacity, disk storage capacity and speed, video adapter performance, monitor size, and so forth, but rarely even mention or consider their power supply. When a system is put together to meet the lowest possible price point, what component do you think the manufacturer will skimp on? Yes, the power supply. To most people, the power supply is a rather nondescript, unglamorous metal box that sits inside their systems, something to which they pay virtually no attention at all. The few who do pay any mind seem concerned only with how many watts of power it is rated to put out (even though no practical way exists to verify those ratings), without regard as to whether the power being produced is clean and stable, or whether it is full of noise, spikes, and surges.

I have always placed great emphasis on selecting a power supply for my system. I consider the power supply the core of the system and am willing to spend more to get a better unit. The power supply function is critical because it supplies electrical power to every other component in the system. In my experience, the power supply is also one of the most failure-prone components in any computer system, especially due to the fact that so many system assemblers use the cheapest ones they can find. A malfunctioning power supply can not only cause other components in the system to malfunction, but it also can damage the other components in your computer by delivering an improper or erratic voltage. Because of its importance to proper and reliable system operation, you should understand both the function and limitations of a power supply, as well as its potential problems and their solutions.

This chapter covers the power supply in detail. I focus on the electrical functions of the supply and the mechanical form factors and physical designs that have been used in PC systems in the past, as well as today. Because the physical shape (form factor) of the power supply relates to the case, some of this information also relates to the type of chassis or case you have.

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