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Troubleshooting Power Supply Issues

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This document pertains to HP and Compaq desktop computers.
Power supply problems can easily be mistaken for other startup issues. Before assuming the power supply is at fault, it is important to first diagnose the nature of the problem in order to find correct troubleshooting steps. To diagnose the problem, plug a grounded power cord from the computer into a grounded power outlet. Once the cable is connected, press the power button on the front of the computer and look at the small light (LED) and fan on the power supply at the back of the computer. Use one of the following links that matches what you see and hear.
Figure 1: Power supply light
Image of the power supply light

Power supply light does not turn on

Perform the following steps until power is restored or it is determined that there is a hardware failure:
NOTE:If the power supply fan spins when the computer is turned on but the light does not turn on, see Power supply light comes on or flashes .
  1. Disconnect everything from the computer, including the power cord.
  2. With the power cord disconnected, press the power button on the front of the computer.
  3. Plug in the power cord to see if the computer turns on. If the computer does not turn on, continue using these steps.
  4. Swap the computer's power cord with the monitor's power cord, and then test to see if the computer can turn on. If the computer does not turn on, continue using these steps.
  5. With the power cord removed, flip the red voltage selector switch to the opposite position. Wait about five seconds, and then switch the red voltage selector switch back to its original location. Ensure that the voltage selector switch is on the correct setting.
    Show me how
    NOTE:Connecting a power supply to a 220V outlet while it is switched to 115V can damage the computer.
    Performing this step ensures that the voltage switch is engaged and set correctly for your country/region.
    Figure 2: Voltage selector switch
  6. Plug in the power cord and test to see if the computer can turn on. If not, continue using these steps.
  7. Plug a lamp into the same outlet to see if the wall outlet has power. Try the computer in a different outlet in order to eliminate the outlet as a possible source of the issue. Test both to see if the wall outlets have power.
    Show me how
  8. Remove all extension cords, power strips, surge protectors and any converters that remove ground. Plug the power cable directly to the wall outlet. Test for power. If this fixes the issue, find the device that is causing the issue and do not use it.
    Show me how
  9. Use a vacuum cleaner to remove the build-up of dust from the power supply fan vent holes. Make sure that the computer is turned off and that the power cord is plugged into a grounded outlet. Only use the end of the vacuum hose near the outside of the fan entrance.
    Show me how
    Figure 3: Power supply vent
    Plug in the power cord and test to see if the computer can turn on. If not, continue using these steps.
  10. If all of the above steps have been tried and the power supply light remains off, use the steps in the next section, Power supply light comes on or flashes , to reseat the cables and check the power switch connector.
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Power supply light is on or flashes

Perform the following steps, in order, until power is restored or it is determined that there is a hardware failure:
CAUTION:This product contains components that are easily damaged by ElectroStatic Discharge (ESD). To reduce the chance of ESD damage, work over a non-carpeted floor, use a static dissipative work surface (like a conductive foam pad), and wear an ESD wrist strap that is connected to a grounded surface, like the metal frame of a PC.
  1. Disconnect everything from the computer, including the power cord.
  2. With the power cord disconnected , press the power button on the front of the computer and wait for ten seconds.
    Show me how
    Plug in the power cord and test to see if the computer can turn on. If not, continue using these steps.
    NOTE:If the power supply fan makes an inconsistent grinding sound or stops and starts erratically, replace the power supply.
  3. With the power cord removed, flip the red voltage selector switch to the opposite position. Wait about five seconds, and then switch the red voltage selector switch back to its original location. Ensure that the voltage selector switch is on the correct setting.
    Show me how
    NOTE:Connecting a power supply to a 220V outlet while it is switched to 115V can damage the computer.
    Performing this step ensures that the voltage switch is engaged and set correctly for your country/region.
    Figure 4: Voltage selector switch
    Plug in the power cord and test to see if the computer can turn on. If not, continue using these steps.
  4. Plug a lamp into the same outlet to see if the wall outlet has power. Try the computer in a different outlet in order to eliminate the outlet as a possible source of the issue. Test both to see if the wall outlets have power.
    Show me how
  5. Remove all extension cords, power strips, surge protectors and any converters that remove ground. Plug the power cable directly to the wall outlet. Test for power. If this fixes the issue, find the device that is causing the issue and do not use it.
    Show me how
    NOTE:If you find the device that was causing the problem was a surge protector, resetting a breaker or fuse on the surge protector might fix the issue.
  6. Remove all attached devices except for keyboard, mouse, and monitor.
  7. Remove any internal component that was recently added, such as video card, memory, CD, DVD, and hard drives. An added device takes more power. The additional power needs can exceed than the power supply is rated for. If the problem goes away when the component is removed, the only option is to upgrade the power supply to a power supply with a higher wattage rating.
  8. Check the power switch:
    Show me how
    With the power cord disconnected, press the power button on the front of the computer. The button should release easily and not stick in the socket.
    If the button sticks, it should be replaced or serviced.
    If the power button does not stick and appears to be functioning, continue using these steps.
    With the power cord disconnected, remove the case or side panel.
    Follow the wires from the power button on the front of the computer to their connection on the motherboard.
    Look at the power switch cables connected to the motherboard. If the cable has become disconnected, connect the power switch cable connector to the connector on the motherboard.
    Figure 5: Power switch connector on Motherboard
    Replace the side panel, plug in the power cord and test to see if the computer can turn on. If not, continue using these steps.
  9. Find the defective part:
    1. With the power cord disconnected, remove the case or side panel.
    2. Disconnect all power cable connectors from their connectors on the motherboard and from the back of internal devices (the back of drives). Make sure to label or remember where each cable connects for future reference.
      Figure 6: Example of common power connections
    3. Replace the side panel, plug in the power cord, and examine the light on the back of the power supply:
      If the LED is on solid and is not flashing, the power supply is probably good and the problem is most likely caused by a defective component (processor, memory, PCI card) or a defective motherboard. Have the computer serviced, or remove the components and replace them, one at a time, to find and replace the defective component.
      If the LED is still flashing (it should not flash with all connectors removed), plug the power cable into a different power outlet that is known to be good. If the LED still flashes, the power supply should be replaced.
      If the LED light is now off, plug the power cable into a different power outlet that is known to be good. If the LED stays off, the power supply should be replaced.
      NOTE: If an electrical storm or power surge has recently occurred, then it is more likely that the power supply, the modem, or motherboard is damaged and requires replacement. If the power supply was damaged due to power outage or storm, this might not be covered under the "act of nature" policy in the warranty statement. Refer to the warranty statement that came with your computer for more information.
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Finding a power supply for upgrade or replacement

Use the following steps before ordering a new power supply:

Step 1: Find the Max Power Rating

Remove the side panel and find a sticker attached to the side of the power supply. This sticker should list a 4x4 part number and the wattage rating. The wattage rating appears as a 3-digit number followed by a W (such as 160w or 300W). The wattage numbers also appear as part of the product name (such as DPS350 or ATX-300). Write down the power wattage and part numbers. If there is more than one wattage number listed, make sure you use the number for MAX power wattage.
Figure 7: An example of text on a power supply label (your label can appear different).
Label showing max power wattage and wattage that you are not to exceed using the 12V leads.
1 - Total rated wattage for the power supply. This is what you use to gauge the overall rating of the power supply.
2 - Extra wattage numbers shown for information only. Numbers like these should not be used to gauge the overall rating.

Step 2: Get dimensions and power supply type

Measure the height, width and depth of the original power supply. You need this information if you are ordering from an online Web site. It also helps to know the type of power supply or case your computer has:
  • Most HP Desktop computers contain ATX power supplies that are 6 inches (15.25 cm) x 5 inches (12.7 cm) x 3.25 inches (8.25 cm). If your computer has a standard ATX power supply, you can replace it with standard ATX power supplies sold by most electronic stores.
  • HP Slimline computers use power supplies that fit into cases that are smaller than ATX. These power supplies are either micro-atx or are of a special design. When ordering a power supply for a slimline computer, make sure to use the original part number (or computer model number) when searching for a replacement or upgrade.

Step 3a: Ordering a replacement power supply

To find an exact replacement part from HP, use the HP Parts Ordering Web site as follows:
  1. Open an HP Parts Ordering Web site (in English). If necessary, select your country/region and language in the upper right corner of the page.
  2. Enter the computer's product name into the corresponding search field. The name of the computer is on a sticker attached to the computer case.
  3. Follow the instructions on the pages to find and view a list of all parts associated with the computer product name.
  4. From the list of parts, find a power supply.
    Figure 8: Example of a power supply part listed on the HP Parts Ordering Web site
  5. If the part is available (has a green check mark), you can order from HP by completing the instructions on the page.
    If you do not want to pay the listed price or the part is not available (has a red X), you can use the part number when searching the Internet or your favorite auction Web site to help find a replacement outside of HP.

Step 3b: Ordering an upgraded power supply

If you want to upgrade the power supply, there are additional things to consider. When adding or upgrading system components, such as memory, optical drives, or video cards, make sure that the power supply you purchase has a wattage rating equal or higher than the total combined wattage of all internal components. Since finding the wattage needed for each component can be extremely difficult, you can use the following general method to find a power supply that will properly provide power to an upgraded system:
  1. Find the power consumption rating of each new component that will be added to the computer.
  2. Total the power consumption ratings from all the new components.
  3. Add the power supply rating of the original power supply to the total. The formula for these three steps is:
    Original max power supply rating + Power consumption rating of new components <= New power supply max rating
    NOTE: You can subtract the power consumption rating for devices that will be removed when upgrading. However, it is better to have a higher wattage number in the event future upgrades are needed.
  4. Purchase and install a power supply that has the same or better wattage rating than the total.
    For example, when installing a new video card that has a power consumption rating of 230W, and the original power supply was 250W, you can install a power supply that is 480W or greater.
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