Understanding and Troubleshooting the PC Power Supply

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The Desktop PC Power Supply

The power supply is the most important component in a desktop PC. It is responsible for providing constant and stable power to the motherboard, processor, video, storage devices and every other component in the system. The power supply can provide this constant power (also known as Direct Current, DC) because it is a transformer which converts Alternating Current (AC) from a standard outlet into Direct Current (DC) needed by the PC; in other words, it is an AC to DC converter.

A bad or poor power supply can cause numerous problems for a PC. A bad power supply can cause lockups, reboots, and generate excessive heat, not to mention shortening the life span of other components. An under powered power supply can also limit system expansion. Sometimes the problem may appear to be from a different component when in fact it is the power supply. We’ve observed installation of software or the operating system failing whenever a power supply is poor.

Another example of misdirection in troubleshooting is a memory error. If a parity check message appears frequently, but not at the same memory location, or is described as random by the end-user, then suspect a power problem.

American Power Conversion has spent millions of dollars advertising the importance of power. Ironically, the power supply is rarely discussed in technical publications and books. In fact, out of 13 computer books offered for sale in a local Barnes and Noble, only two devoted more than a paragraph or two to the topic of power.

Buying a Computer for Dummies doesn’t even list ‘power supply’ in its index. Robert Stephens and Dale Burg in The Geek Squad Guide to Solving any Computer Glitch only make reference to two types of troubleshooting:

  • Make sure the power supply is plugged in, and
  • Check the 115/220 switch.

The book Building Your Own PC, Pentium III edition shows the wrong power supply. The picture and text discuss the AT power supply, and in fact, the book devotes two pages to installing and troubleshooting the AT power supply. For those of you a bit confused, most Pentium III desktop PCs are equipped with an ATX power supply.

With such a dichotomy between the importance of the power supply and publications, it is no wonder that technicians rarely look toward the power supply as a cause for problems.

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