If your desktop computer isn't powering on, then you may have a problem with the power supply. Testing the unit is simple and requires a few inexpensive tools. Below is what you need to know about power supplies, how to remove one from your computer and how to test it for proper functioning:
What is a power supply?
Desktop computers contain numerous components that require varying amounts of electrical power for operation. Hard drives, CD drives, cooling fans, graphics cards, and motherboards are a few of these internal devices that need electricity to function. The power supply serves to distribute electricity in the appropriate voltages to each component; it receives 120 volts AC from the wall outlet, converts voltages and routes it into the computer.
If something goes wrong with the power supply, chances are likely your computer will malfunction or fail to turn on entirely. You can perform the following test procedure to determine if your computer's power supply is the culprit for your problems:
Electrical multimeter capable of measuring DC (direct current) voltages
Screwdriver or nutdriver
1. Remove the access panel to your computer - Before beginning, place your computer on a steady, well-lit work surface and lay it carefully on its side. Most desktop units use a sliding panel that allows access to the internal components, so locate the screws or latches that permit you to loosen and remove the panel. The power supply for the computer should be easy to find; it will consist of a silver-colored box with multiple wire harnesses of varying sizes leading from it.
2. Remove the power supply from the computer - After locating the power supply, you need to detach all the wire harnesses from the various internal components. Some harnesses are removed by simply pulling the connector away from the component, but be on the alert for connectors that use a clip to hold them in place. To remove these, simply squeeze the clip and then lift the connector free from its socket. Detach all the wire harnesses from their components and carefully gather them together in a loose bundle.
Once you have detached the wire harnesses, look on the back side of the computer's case and locate the 3-prong outlet where the power cable is attached. You will notice several screws surrounding the outlet that hold the power supply in place. Remove these screws with a screwdriver or nutdriver and set them aside where they won't be lost. Gently pull and lift the power supply box out of the computer case, but be careful not to dislodge any other components during the removal. If you encounter binding or the power supply will not lift free from its attachment, closely check for overlooked connections and missed fasteners.
3. Power up the unit - Following removal of the power supply unit, prepare it for testing by installing an electrical "jumper". To do this, locate the largest wiring connector, the 24-pin harness, and find the green wire leading into the connector. Bend an ordinary non-insulated, non-painted paperclip into a "U" shape. Next, insert one end of the modified paperclip into the opening on the connector that is attached to the green wire, then push the other end of the paperclip into an opening attached to any one of the black wires.
Once the jumper is in-place between the green wire and one of the black wires, plug the 3-pin power cord into the 3-pin outlet on the power supply box. If the cooling fan on the power supply begins working, then proceed to step 4. If you don't obtain any response, check the power supply for an on/off switch and turn it to the "on" position.
4. Check voltages - While there are a multitude of wires leading from the power supply, the system is designed to be easy to test. Each wire is color-coded according to voltage or function, and this is important for identifying proper voltages when comparing to your multimeter readings. Reference a table that provides a reference for relevant wire color and associated voltages.
For the purposes of this testing, you can ignore other color wires, such as brown, purple, or gray, and the black wires are all grounded leads with no current.
To check the voltages, power on and set your multimeter to read voltages in the zero-to-20 volts DC range; if you aren't sure how to do that, consult your owner's manual for help. Then, select any one of the wiring connectors to begin testing; it doesn't matter which one you select first.
Next, insert the black lead tip from the multimeter into any one of the connector openings attached to a black wire and the red lead tip into a connector opening attached to one of the colored wires listed in the table. Read the voltage from the meter display and reference the voltage table to see if the reading is within one-half of a volt of the normal voltage. As long as it is, then that particular wire lead is functioning normally.
Leave the black lead tip inserted in the same opening and move the red lead tip from one connector opening to another until you have measured all voltage outputs. Once you have tested all voltages on a given connector, move to another connector and continue testing until you have measured all voltages. If at any point the measured voltage exceeds the one-half volt range threshold, that indicates the connection is bad and the power supply will likely need replacement.
Contact a company like Nation's First Office Repair if you have specific questions about ways in which your computer is malfunctioning.