Troubleshooting Power Supply Issues


Power supply light does not turn on (or no power supply LED)
Power supply light on or flashes

This document pertains to HP and Compaq desktop computers.
This document is about troubleshooting power supplies. Power supply problems can be easily mistaken for other startup problems. To try and isolate the problem and use the correct troubleshooting steps, please plug the power cord in, and press the power button on the front of the computer. Read each of the following startup conditions carefully, and then click the corresponding link to go to the correct troubleshooting steps:

1. If the lights on the front of the computer come on or the power supply fan spins, refer to the HP Support document Resolving Startup Problems (this is another support article).
2. The small LED on the power supply is missing or does not light and the fan in the power supply does not spin. Please use the steps in Power supply light does not turn on .
3. The small LED on the power supply comes on and remains lit. Please use the steps in Power supply light on or flashes .

Figure 1: Power supply LED

Power supply light does not turn on (or no power supply LED)

Perform the following steps, in order, until power is restored or it is determined that there is a hardware failure:
NOTE:
If the Power Supply fan spins when the PC is turned on but the light does not come on, it is possible the LED is defective. If this is the case, use the section Power supply light comes on or flashes .

1.Disconnect everything from the PC, including the power cord.
2.With the power cord disconnected, press the power button on the front of the computer.
Plug in the power cord and test to see if the computer can turn on. If not, continue using these steps.
3.Replace the power cord with another power cord, like the one used by the monitor.
Test to see if the computer can turn on. If not, continue using these steps.
4.Ensure that the voltage selector switch is on the correct setting, 115V for North America.

Figure 2: Voltage selector switch

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.
This ensures that the voltage switch is engaged and set correctly for your country/region.
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.
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.
9. Use a vacuum cleaner to remove the build-up of dust from the power supply fan vent holes. Make sure that the PC 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.
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, use the next section Power supply light comes on or flashes , to reseat the cables and check the power switch connector.

Power supply light 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.
Disconnect everything from the computer, including the power cord.
With the power cord disconnected, press the power button on the front of the computer for five seconds.
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
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, 115V for North America.
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.
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.
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.
NOTE:
If you find the device that was causing the problem was a surge protector, resetting a breaker or fuse on the surge protector may fix the issue.
Remove all attached devices except for keyboard, mouse, and monitor.
Remove any internal component that was recently added, such as video card, memory, CD, DVD, and hard drives. An added device may take more power 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 power supply with a higher wattage rating.
Check the power switch:
With the power cord disconnected, press the power button on the front of the PC. 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.
Find the defective part:
With the power cord disconnected, remove the case or side panel.
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
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.