3.14.3 Troubleshooting Power Supplies

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Following are tips for troubleshooting power supplies.

• Familiarize yourself with the symptoms of a bad power supply.
  • The computer does not turn on.
  • The computer sporadically shuts off or reboots.
  • A broken or noisy fan.
• Rule out the obvious before opening the computer. Make sure:
  • The power cord is plugged into the wall.
  • The power switch is in the on position.
  • The voltage switch is set to the correct voltage.
• Test the power supply using a multimeter or power supply tester. Voltage levels should be within +/- 5% of normal. If they aren't, the power supply is bad or failing and you should replace it.
  • 12 V rail should be between 11.4 and 12.6 volts.
  • 5 V rail should be between 4.7 and 5.25 volts.
  • 3.3 V rail should be between 3.1 and 3.4 volts.
• Take proper safety precautions. Power supplies carry dangerous levels of electrical current. You should:
  • Never ground yourself when working on a power supply.
  • Never open or disassemble a power supply. Always replace the entire unit.

Some computer manufacturers, such as Dell or HP, produce proprietary power supplies. These power supplies might have a unique shape or use different wiring schematics on connectors. When replacing a power supply, identify whether a standard ATX or a proprietary power supply is required.

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