Adding Components

If you are choosing a power supply for use in a new computer, review your proposed computer design carefully. Make a list of the wattage requirements of all the hard drives, floppy drives and optical drives in your system. Add them all up: The total will be the minimum wattage your power supply should support. There are also helpful websites, such as eXtreme Power Supply Calculator, that make the process of finding your necessary wattage easy.

Types of Connectors

For many years, the standard for fans and hard drives has been the Molex connector. This is a flat white plug with four wires and connectors. It provides +12 volt with the red and +5 volt with the yellow. The two black wires are ground wires. Most recently manufactured power supplies include a Serial ATA (SATA) power plug for newer hard drives. This is a flat plug fed by a narrow ribbon, with an L-shaped connection.

Other Connections

The modern power supply is called a switching power supply, because it uses switching technology to convert the alternating current (AC) from a power outlet into direct current (DC) inside the computer. It must detect a load to stay in operation, a built-in safety function that will turn off if the hardware fails. A small orange or gray wire usually has to be grounded through the computer's motherboard to keep the power supply on.

Colors and Voltages

The power supply provides several voltages to the computer based on the color of the wire attached. You will see several different colors in the large connector that attaches to the motherboard. They are the following voltages: red = +5v, blue = -12v, yellow = +12v, black = ground.

Safety Precautions

Any time you are working inside the computer, you should unplug it from the wall to prevent the chance of electrocution. Never open the power supply, even when the computer is unplugged, because it contains capacitors that can hold a charge for up to a week after you have unplugged the unit; this charge is large enough to cause serious injury or fatality.

The power supply unit (PSU) in a desktop computer is a component that converts mains AC current to the DC current that the computer requires. High voltages would destroy the internal components of the computer, such as the CPU and memory chips. The PSU is responsible for stepping down DC voltages to the lower voltages that power the internal components. Some PSUs have switching capabilities that allow them to be used in both 240-volt and 115-volt environments. These PCUs have an external switch so that the user cab choose the input voltage.

Casing

The PSU case keeps the internal components of the PSU isolated from the components inside the computer case. Some of the PSU components carry voltage that could do considerable damage if they were to access computer components. The case insulates against electromagnetic interference generated within the PSU.

Drive Connectors

PSUs usually have at least five power connectors for delivering power to internal components not fixed to the motherboard. Typically, this includes hard disk drives and CD/DVD devices. Different cable and connector types are needed to connect PSUs to different devices, such as IDE-based drives and SATA-based drives. If more power connections are required, the number can be increased by using splitters, which create two connections from one.

Motherboard Connectors

Power is sent from the PSU to the motherboard via specific wired connections. The CPU, expansion slots, memory and other components all need to receive the correct voltage from the PSU, and there are locations on the motherboard designed to receive the PSU connections. Connections to the motherboard must be made accurately, since the wrong connections can result in damage to the computer.

Cooling Fan

In early computers, the PSU fan was the primary cooling source for the whole computer. The PSU fan is located inside its casing. Having the fan control the incoming air means that filters can be used to limit the amount of dust getting into the computer case. More recently, this mechanism was switched when more powerful processors needed additional cooling.

Power Cable

A power cable runs externally from the PSU case and is connected to the mains using a three-pin plug. The cable connects to the PSU using a standard three-point connector, which is similar to the connector on kitchen appliances. Some PSUs also have a pass-through connector, which allows them to feed mains power to other external components, such as monitors.

Desktop computers get their power from a built-in power supply. When you look at the back of your computer notice the power cord; this plugs directly into the power supply which is located inside your computer case. Power supplies can fail due to several common problems. Some of these can be solved others; will require replacing your power supply. Power supplies are not expensive and moderately easy to replace.

Checking Power

The most common problem with power supplies is no power. Check your outlet and make sure it is operational. Remove any power strip or Uninterruptible Power Supply (UPS) and plug your computer directly into a good outlet. In addition, make sure the power cord going to your computer is good and that it is completely plugged into the power supply .

Power Supply Switches

A small slider switch is on the power supply. This switch is usually red and is marked 115V or 230V. This is the voltage setting for the area of the world you reside in. Make sure the switch is set in accordance with your local voltage. Also, there is usually a rocker switch marked with a circle and a straight line; this rocker switch should be set with the line side pressed down and the circle up. The line indicates your power supply is on.

Overheating Power Supply

Another very common issue is overheating. If your computer turns off after a few minutes or a few hours, this could be the problem. Computer power supplies have a ventilation fan and vents that must be cleaned periodically. If your computer is under warranty, contact your seller; if not your should clean the cooling vents. Unplug the power cord from the back of your computer; remove the cover from your computer and vacuum the vent on your power supply, which is located on the back of your computer. Then vacuum the vent slots on your power supply located inside your computer. You will also find other vent holes in the computer case itself. You must clean those as well.

Overloading

Power supplies are rated to handle only so much current. Every device plugged into your computer draws power from the power supply; sometimes these devices can fail and draw too much power. Unplug every external device except the keyboard, mouse and monitor. Apply power to your computer. Then test each device one at a time to see if that device is causing your power supply to shut down. In addition, if you have too many devices plugged into your computer, you may overloading your power supply.

Replacing Your Power Supply

If the above steps do not fix your problem it is moderately easy to replace your power supply. Find out if you have an AT or ATX power supply and what size power supply you need. You can order a standard power supply.When replacing your power supply, note where the cables are plugged into, remove the old power supply, install the new one and plug in the cables.

Troubleshooting Desktop Power Supply

Introduction

Hitting the power button on your desktop computer and having nothing happen can be frustrating. Getting the problem diagnosed and fixed can be expensive. Some problems are minor and/or easy to fix on your own as long as you can identify them. Before any work is done on a desktop power supply, you need to analyze the symptoms.

Preparation

Before opening the case of the tower, you need to check some of the easier reasons for why your desktop computer won't power up. Check the power source itself. Go to the breaker box to see if the breaker hasn't been tripped. Your next step is to check the equipment tied to that power source. Check your power cord by switching it with another one. This is fairly easy and requires no tools. Pull the cord from the back of the computer and trade it with the cord from the back of the monitor. Press the "Power" button and wait to hear the normal whirring sounds that accompany the computer when it is coming to life. If nothing happens, move on to the surge protector. Check to see if other items plugged into the surge protector are getting power. You can also plug the desktop power cord into a different plug in the surge protector to see if just that one outlet is the problem.

You are still not ready to open the case. Check the warranty of the machine. If the warranty is still valid, you can send it back to the manufacturer for repair. If you purchased an additional warranty or repair plan from the store you purchased the desktop from, you can call them about steps for repair. If your warranty has expired and you don't want to pay for costly repairs, you will have to open the case and fix the problem yourself. Before doing this, find an anti-static material to place around the area to avoid damage to the hard drive and other components.

Checking Components

Since you've made sure the problem isn't tied to the power source, check the equipment inside the computer case. Using a screwdriver, remove the case. Check the power supply to see if it is connected to the motherboard . Power problems are sometimes tied to other hardware components that are hindering the power supply from doing its job. Check the motherboard closely for cracks and burns. Sometimes if the motherboard is damaged, power can't be supplied to it any other components. If the motherboard seems fine, check other components connected to the power supply's cables. Remove the cables one at a time and try to turn on the computer. If the computer turns on after one of the components has been disconnected, then the problem lies with that component and not the power supply. You should also try removing any items in the PCI expansion cards, RAM chips and video cards. Even if a power cable isn't tied to them, they can hinder the computer from not turning on.

Your last try is to replace the power supply. If nothing else seems to work, replace it with a new one. Most likely, this will fix your problem and power will be restored to your desktop computer. If, after replacing the power supply, the computer still won't turn on, the problem lies with one of the components listed above. Check them again for any damage.

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