How to Diagnose and Replace a Failed PC Power Supply |
How to Diagnose and Replace a Failed PC Power Supply
originated by:James Quirk, Anonymous, Ben Rubenstein, Tom Viren (see all)
Article
When a PC power supply dies or begins to wear out, it must be replaced. With a few simple tools and the help of this guide, you can do this job yourself and save on expensive repair fees.
1 Familiarize yourself with proper ESD procedures before doing any kind of PC repair work which requires opening a computer. If you neglect this step, you may damage your computer.
2 Verify that the power supply needs replacement. The most obvious clue is that the system will do absolutely nothing when you hit the power button. If there is no sound and no monitor activity of any kind, the power supply has probably died. While this can also be caused by a faulty switch, it is usually the result of a burned-out power supply. Another clue is that the system boots, but the system makes rapid, short beeps repeatedly and does not boot.
Test the power supply. Use a power supply tester (typically between $10 and $20 USD).
Test basic functionality. Disconnect the power supply from the motherboard. Take a paper clip and short pins from the green and any black terminal of an ATX power connector (largest connector, typically 20-24 pins total) to power it on. Leave the paper clip connected, if you remove it, the Power will shut down again. Check to see if the fans spin (ie: inside the power supply). If so, your power supply is providing a 12V supply. An obvious clue of component failure is faint smoke or a burnt smell.
3 Once you are satisfied that the power supply is the culprit, disconnect all external connectors (including the power cord) from the machine. This may include keyboard, mouse, network cable, speakers, etc.
4 Remove the case cover, placing any screws somewhere where they will not get lost.
5 Identify the power supply unit. It will be connected to almost every component inside the computer case and will look something like this:
6 Using proper anti-ESD practices, disconnect all connectors which run from the power supply to the devices inside your PC.
7 Unscrew the mounting screws on the back of the case which hold the power supply in its housing. Place the screws in a handy location.
8 Gently remove the old power supply from the case. This is usually a simple process, but if there is very little room in your PC, it may be necessary to remove other components in order to get the power supply out. If you don't feel comfortable removing other components, replace the mounting screws and enlist the help of a PC expert before continuing. Do not try to yank a power supply out by force.
9 Purchase a new power supply of the same type as the old one. Most power supplies used in modern computers are of the "ATX" variety, but if you aren't sure, take the old unit to the store with you to compare. The simplest rule of thumb is that the new unit should be exactly the same width as the old one. It's fine if the new unit is a bit longer, as long as it will still fit into your case. Do not hesitate to ask the salesperson or technician for help in identifying the correct unit to purchase.
10 Unpack the new power supply and make sure it physically fits correctly. If the new unit has a large bottom mounted fan, the bottom rear bottom flange on some cases might get in the way. Add it to the case in the same place the old unit was, and use the mounting screws to fasten it down.
11 Using proper ESD procedures, connect the devices in your PC to the new power supply. The connections should be the same as they were before. It can require a bit of force to insert power connectors correctly, but if if you have to strain a great deal to push them in, you may be trying to connect them backward. It is very difficult to connect most Molex connectors improperly, but if you are determined (and strong) enough, it can be done. If you have to force too hard, try turning the connector around.
12 Verify that no cables or unused connectors are stuck in the CPU fan or touching other moving parts. If the CPU fan is stopped by a loose connector (or any other obstruction), the processor can be destroyed very quickly. You may wish to restrain unused cables to prevent them from getting tangled up in fans.
13 Replace and fasten down the case cover.
14 Replace all external connections to the back of the computer (power cord, mouse, keyboard, monitor, network cable, speakers, etc).
15 Power up the system and enjoy.
16 If your system doesn't start up correctly here, your failing power supply could have taken out the motherboard.
Tips
If you suspect that your power supply is dying, replace it. A common clue which indicates a failing power supply is a high-pitched whining or grinding noise from the area of the case where the power supply is housed. Don't wait until the supply dies, because its failure can cause voltage problems which can ruin your motherboard, hard drive, or other components.
Invest in a high quality power supply. Do some research before you purchase one. More wattage on the package doesn't mean better. Most home PCs don't actually use more than 300W even though this is not what power supply marketing people want you to know. The unit should provide adequate wattage for your needs. Don't skimp on the power supply, as you may regret it later. Power supplies that fail can damage other components in your computer, especially the motherboard.
If you've gone through multiple power supplies in a short period of time you MAY have a faulty outlet. This is exacerbated by cheap power supplies as they are not hardy pieces of equipment.
If you purchased a marginal power supply it is possible that the start up current demand from the hard drives could push demands over powe supply's limit. Power supply wattage have "maximum" definitions which may benefit the manufacturer. If two power supplies both have "switching" designs and made by brand name manufacturers consider using their weight as a sign of ability. Larger heat sinks and capacitors weigh more.
Warnings
If it's hard to remove a hard drive or CD/DVD drive power connectors, don't pull on it hard. It will come out suddenly and you'll likely cut your hand on sharp edges. Wiggle gently as you pull out.
Don't attempt to open a power supply unit to attempt repairs or experiment with the parts if you're not familiar with working with high voltage circuits. The primary side of power supply operates around 340V DC. Power supplies contain capacitors which can hold dangerous charge for a few minutes. Usually the integral bleeder resistor ensures the capacitor does not remain charged for much longer than a few minutes. Most problems are not repairable by the home user. Refer the unit to a qualified electrician, or better yet, recycle it and replace it with a new or refurbished one as described here. The cost of having a power supply repaired is often more than the cost of a replacement unit.
Sometimes, a failing power supply can continue to boot the system, causing only minor lockups and shutdowns. If this is the case, you should try to rule out other problems before replacing the power supply. While it is always best to replace a power supply you have good reason to believe is faulty, you should be sure that the problem is not caused by other factors.
Do not do this on Dell Computers! Some Dell computers are designed to use an odd connector. If you use a standard power supply you may damage the power supply, the motherboard or both! This also goes for Compaq, some HP and other brand-name PCs. Check first! The Dell used the SAME ATX connector as normal systems but wired it in a non-standard way - this is actually worse than a different connector because it looks the same but was deliberately wired incorrectly.
Some replacement power supplies have what is called a 20+4 motherboard connector. These connectors work with either 20 or 24 pin motherboard connectors and will accomodate more types of computers. The 4 extra pins clip onto the end of the standard 20 port clip. This may be shipped with the 4 pin clip attached and the clip may not fit well on a 20 pin connector which could result in startup failures. Before you blame the new power supply, determine if your motherboard input connector is 20 or 24 pin. If it is 20 pin, make sure the 4 pin clip is detached and reconnect the clip to your motherboard, it should fit better and this may correct intermittent startup problems that might be occuring.
Things You'll Need
Phillips-head screwdriver
Replacement power supply
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