Diagnose and Replace a Failed PC Power Supply

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.

Steps

Diagnosing a Failed PC Power Supply

  1. Make sure that everything is plugged in. It's entirely possible that a cord could just slip out from the outlet while you're working. If power is present to the monitor and other peripherals, yet there is no power to your computer, there is likely something wrong with your power supply.
  2. Hit the power button. 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.
  3. Look at when your computer boots up. Noticeable changes in how long it takes for your computer to boot up and shutdown, as well as spontaneous rebooting, could be a sign that something is wrong.
  4. Check for beeps. If the system makes rapid, short beeps repeatedly and does not boot when you try to get it to, this could be linked to the power supply.
  5. Observe any computer failures. If there are system startup failures or lockups, memory errors, HDD file system corruption or USB power issues, this is often directly related to your power supply.
  6. Check the fan in your computer. If the fan in your computer is failing to spin, it could lead to overheating and smoke in the system, all of which can cause a failed power supply.

Removing a Failed PC Power Supply

  1. Familiarize yourself with proper ESD procedures. This should be done before doing any kind of PC repair work which requires opening a computer. If you neglect this step, you may damage your computer.
  2. Disconnect all external connectors (including the power cord) from the machine. This may include keyboard, mouse, network cable and speakers.
  3. Identify the power supply unit. It will be connected to almost every component inside the computer case and will look something like this:
  4. Remove the case cover. 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.
  5. Gently remove the old power supply from the case. This is usually a simple process, but if there is little room in your PC, it may be necessary to remove other components 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.

Replacing a Failed PC Power Supply

  1. 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.
  2. 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.
  3. 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.
  4. 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.
  5. Replace and fasten down the case cover.
  6. Replace all external connections to the back of the computer (power cord, mouse, keyboard, monitor, network cable, speakers, etc). Power up the system and enjoy your new power supply.
    • 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 because 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 the power supply limit. Power supply wattage has "maximum" definitions which may benefit the manufacturer. If two power supplies both have "switching" designs and are made by brand name manufacturers, consider using their weight as a sign of ability. Larger heat sinks and capacitors weigh more.
  • If you don't own a power supply tester, large electrics and computing stores may be able to test a power supply for you. Maplin, a store in the UK, does not charge for this service.

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.
  • 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 and 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.
  • Electrostatic Discharge (ESD) is harmful to computer hardware. Be sure to wear an anti-static wrist-strap that's properly grounded to eliminate ESD before working on the power supply. The easiest way is to wear the anti-static wrist-strap and attach the alligator clip to the case of the computer.
  • 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.
  • 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. Power supplies contain capacitors which can hold dangerous charges for a few minutes. Refer the unit to a qualified electrician, or better yet, recycle it and replace it with a new or refurbished one The cost of having a power supply repaired is often more than the cost of a replacement unit.
  • 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 accommodate 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 start-up problems that might be occurring.

Things You'll Need

  • Phillips-head screwdriver
  • Replacement power supply

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