Section 1.9. Power Supply and Battery

1.9. Power Supply and Battery

Your computer's power supply lives inside the PC's case, where it converts the wall outlet's 120 volts into the lower voltage sucked up by your computer's parts . It needs attention only during two main events: if you spot a ton of dust clogging its main fan, and when your PC refuses to turn on. A few swipes with a vacuum cleaner's brush attachment (Section 1.3.1) solves the first problem, but the second one is much more complicated. Luckily, most people never need to tackle replacing their power supply; the computer usually wears out first.

Note: Don't confuse a PC's power supply with an Uninterrupted Power Supply (UPS). The PC's power supply is a small box that lives inside your PC. A UPS (Section A.3.3) is an optional add-on, usually in the form of a large, heavy box that sits outside your PC to protect your work from power outages.

If your desktop PC's power switch doesn't seem to have any effect, do what the techies do: put your ear to the computer case and listen closely for any sounds. Normally, turning on the computer starts the power supply's whirling fan. But if you can't hear the fan blowing air over your PC's partsnor any other noises inside your PCthen the power supply is dead and must be replaced .

Before jumping to this unpleasant and rare conclusion, try a few sure-fire tests:

  • Press the power button for about 10 seconds, and then wait another 10 seconds. Then press the power button again. Repeat. Sometimes that's all it takes to resuscitate a frozen PC.

  • Juggle the power cord in its outlet, and where it plugs into the back of your PC. It may be loose.

  • Check the little red switch on the back of your PC to see if a practical joker has switched it to 220 from 110 (see Section

If you're still seeing no signs of activity, your power supply is dead.

In fact, if the power supply's fan stops working but your computer still runs (Section 1.4), you still need to replace the power supply. Without the power supply's cooling fan, your computer will overheat, leading to even more expensive repairs . When your power supply needs replacing, the next section explains how to handle the chore.

Warning: Even after you unplug the power supply, its internal capacitors store up dangerous amounts of electricity. Don't try to pry open the power supply's case and repair it yourself. You have to replacenot repairthe power supply.

1.9.1. Replacing a Dead Power Supply

Yes, even unplugged power supplies contain dangerous amounts of electricity. And yes, replacing one sounds like a stunt from a reality TV show. However, the dangerous parts are sealed inside the power supply's metal box, away from sensitive fingers.

Many people prefer the convenience of letting a repair shop handle the job of performing this transplant procedure. Replacing the power supply yourself, however, saves money, results in a better power supply, and gives you a conversation starter at cocktail parties. If you're handy with a screwdriver, your first step is choosing the right replacement.

When shopping for a replacement power supply, you need to know the replacement's proper wattage , which is the maximum amount of power it can feed to your PC. You also need to know its physical size , so it screws back into the same place as the old one.

Quieting a Noisy PC

Newer PCs sound much quieter than older models, but you'll almost always hear a constant whine. The biggest noisemakers? The fans that cool the sweat from your PC. The biggest (and noisiest) fan cools your power supply; another cools your CPU. And if your computer's built for games or other demanding graphics software, a third fan cools your video chip. Some even add a fourth fan to cool the hard drive.

Replacing the power supply gives you a great chance to shush your computer. The two prime power supply vendors , PC Power and Cooling and JS Custom PCs, sell quiet models with high-quality ball bearing fans, extra insulation, and other ways to dampen the noise. Building the Perfect PC (O'Reilly) lists more information about quieting a noisy PC when building one from scratch. Finding the replacement's correct wattage

If you haven't upgraded your PC with additional parts, buy a replacement power supply that's the same wattage as your old power supply. Look for your old power supply's wattage, usually between 200 and 300 watts, stamped on a sticker along its top or side. You may need to first remove the power supply from the computer case (Section 1.3) to see the sticker.

But if you've upgraded your PC, especially by adding a faster video card or extra drives , your original power supply probably isn't dishing out enough wattage. In fact, the upgrade's extra drain may have put the final knife into your old power supply's ailing heart. How then do you know how many watts to buy for your replacement?

To answer this admittedly difficult question, vendors like PC Power and Cooling ( and JS Custom PCs ( offer free online wattage calculators . If you check off your PC's main parts on the Web site's form, the site tallies up your computer's wattage requirements.

Tip: Google the phrase "power supply wattage calculator" to find similar wattage calculators and compare notes.

When in doubt, buy a replacement with more wattage than you need, despite the higher cost. For an extra 20 to 40 bucks, those extra watts offer room for future upgrades, as well as peace of mind. Plus, buying a high wattage power supply isn't like replacing all your nightlights with 100-watt bulbs . Your computer draws different amounts of power depending on its current task, so the power supply dishes out only what the computer currently needs. If your computer doesn't need extra power, the power supply won't suck extra power from your outlet. Buying a replacement power supply that fits your case

Power supplies come in several sizes, but the vast majority use a size called ATX , named for the Advanced Technology eXtended moniker that Intel slung onto its motherboards in 1995. If your computer's strong enough to run Windows XP, it's probably using an ATX power supply, widely available both online and at computer stores.

Your computer's packing slip, the sticker on the old power supply, or the PC manufacturer's Web site (Section 1.1) can usually tell you what size you're looking for. Searching online for the power supply's part number (found on its sticker), often turns up a vendor for hard-to-find power supplies, as well.

A Power Supply's Voltage and MTBF

The power supply converts the standard 120 or 240 volts of AC power into the lower DC voltage your computer needs. Circuits, like those in the memory and motherboard, want either 3.3 or 5 volts, but the moving parts (drive motors and fans) insist on 12 volts.

Power supplies come rated mostly by MTBF (Mean Time Between Failures). A MTBF rating of 100,000 hours means the manufacturer estimates it will die after constantly powering your PC for about 11 years under ideal conditions.

If you've blown through several power supplies, call your electric company and ask them to test your outlet for power fluctuations. These electrical spikes can reduce the power supply's life considerably. Also, plugging a computer into a UPS (Uninterruptible Power Supply) filters the line, prevents voltage spikes, and lets you wring the most life from your power supply.

For a higher quality replacementone bearing both an accurate wattage rating and a long lifebuy from a third-party vendor like JS Custom PCs or PC Power and Cooling.

Warning: Many Dell computers don't use standard power supplies, and the voltage difference can toast your computer's motherboard. When replacing a Dell PC's power supply, make sure the replacement is designed specifically for a Dell computer.

But if you're having trouble finding a replacement, call your PC's customer support number and buy a replacement directly from the manufacturer. Although the power supply won't be as high-quality or quiet as one from a third-party manufacturer, you'll still save money by installing it yourself.

Warning: Don't skimp when replacing your power supply. It feeds electricity to every part in your computer. High-quality power supplies keep the power flowing at a constant rate; cheaper ones can cause subtle fluctuations that shorten the life of your PC. Replace the old power supply

After opening your computer case's (Section 1.3), look in the back of the computer for the three or four screws surrounding the topmost fan. (That fan, located adjacent to the power cable, lives inside the power supply itself.) Inside your computer, usually near the top, the power supply clings to the back wall with those screws. The power supply lives in a gray metal box that has dozens of colored wires poking out of it (see Figure 1-4). When you find the power supply, follow these steps to remove it and install the replacement.

  1. Remove the power cord between the computer and the wall, and then unplug all of the power supply's cables and connectors .

    Remove the PC's power cord first, both from the wall outlet and from where it pushes into the power supply.

    Next, look inside your computer to find the thick bundle of wires protruding from the power supply. Locate where the wires plug into your motherboard (Figure 1-24) and into your drives (Figure 1-25).

    Tip: As you unplug wires, consider drawing a quick diagram of how the various plugs fit into their jacks so you can push the new ones into the same places.

    First, remove the largest plug from its jack on your motherboard, shown in Figure 1-24. If you spot any other plugs or wires leading from your power supply to the motherboard, unplug them from the motherboard, as well.

    Figure 1-24. The power supply's largest plug provides power to the motherboard, where it's shuttled off to other parts as required. To remove it, pinch in the little latch on one side of the plastic connector and pull the connector straight up. (Don't tug on the wires, no matter how tempting.) The plug fits into the motherboard's jack only one way, with the plug's latch clasping onto the motherboard jack's latch.

    Note: When removing or inserting plugs into jacks, pull on the plastic connector, never on the wires. Too much stress on the wires may pop them out of their connectors. (If a pair of needle-nose pliers can't put the wires back into the connector, bring your PC to the repair shop, beg for mercy, and ask them to refasten the wires with their "Molex Pin Extractor" and "Molex Crimp Tool.")

    Next, remove the smaller plugs (called Molex connectors) from their sockets on the back of your drives, shown in Figure 1-25. Finally, disconnect any cooling fans that connect to the power supplyyou sometimes find fans cooling high- powered video cards, as well as the CPU.

    Figure 1-25. Most drives connect to the power supply with the large plastic Molex connector. Be sure to grip the plastic connector itself, not the wires, which can pull out of the plug amid much cursing. The Molex connectors sometimes take a little sideways motion to loosen their grip. The connectors reattach to the drives only one way, so you can't plug them in the wrong way.
  2. Remove the screws holding the power supply to the case, and remove the old power supply .

    Locate the screws surrounding the fan on the outside of the case. Depending on your PC's model, remove two, three, or four screws. Save the screws in an egg carton or ice cube tray. You may need to snap off plastic cooling ventslarge snap-on molded plastic shafts that direct the air around the CPU. Save the vents for the new power supply.

  3. Attach the new power supply .

    Locate the screws you removed in Step 1 and attach the new power supply. The holes in the power supply line up exactly with the holes in the case; if they don't, your power supply is upside down, sideways, or the wrong size. Reattach any plastic cooling vents you removed earlier.

  4. Set the correct voltage for your country .

    A little red switch beneath the power outlet, shown in Figure 1-26, lets you set the voltage to either 110/115 volts (North America and Japan) or 220/230 volts (most European countries ). If necessary, flip the power supply's little red switch to match your country's voltage.

    Figure 1-26. A little red switch on the back of the power supply lets you toggle the voltage between 110/115 to 220/230. Although it's usually set for 110/115, many countries manufacture and sell power supplies. If it's not set to your correct voltage, use a little screwdriver to flip the switch so your correct voltage shows.
  5. Attach the new power connectors to their jacks .

    Reattach the wires to the motherboard, your drives, and any cooling fans.

    When finished, plug your old power cable into the back of your power supply. (Most power supplies don't come with new power cables.) Don't plug it into the wall yet, though.

    Don't be surprised to see some of your power supply's wires dangling unused. They're for upgrades you may install later.

  6. Reattach the case panel, plug in your PC, and turn it on .

    Your PC should whir back into action. If it doesn't, turn it off and make sure you fastened your motherboard's connectors tightly in the right places. Try pushing the power cord tightly into the back of your computer, too; sometimes that doesn't make a good connection. If your PC still doesn't turn on and you don't even hear the power supply's fan, somebody sold you a dud. Exchange it for a new one.

When you're sure the new power supply works, feel free to throw away the old one. (Some hobbyists save them in case they need to salvage a Molex connector.)

1.9.2. Replacing the Motherboard's Battery

Just like a cheap pocket calculator, your expensive PC contains a battery. Without it, your PC would forget the date, time, and the names of its parts whenever it's unplugged or loses power. Batteries last a fairly long timefrom three to seven years. The first symptom of a dead battery? Your PC complains about its amnesia when turned on, leading to odd error messages occasionally mentioning the words BIOS or CMOS (Section 17.1).

Luckily, replacing the motherboard's battery is a cheap and easy fix.

Tip: Most motherboards use 2032 lithium batteries, an inexpensive battery about the size of a quarter. Since your motherboard probably uses one, too, save time by picking up a replacement 2032 battery at a nearby camera store, electronic supply store, or even a drug store.
  1. Turn off the computer and remove its side panel or case (Section 1.3) .

  2. Locate the motherboard's battery .

    A small round silver disc (as shown in Figure 1-27), the battery usually lies flat in a small plastic holder.

    Figure 1-27. A flat, round battery on the motherboard lets computers remember the time and date when you unplug them. To replace the battery when it's dead, pop it out of its holder and push in a new battery, available at most computer shops , drug stores, and office supply stores.
  3. Remove the battery .

    Note which side of the battery faces up, so you can insert the new one the same way. Next, unlatch the battery and lift it from its holder. Sometimes just pressing down on one edge of the battery pops it from the holder.

  4. If necessary, buy a replacement battery that matches the old one .

    Most, but not all, computers use 2032 lithium batteries. (The number's stamped onto the battery's flattest surface.) If you haven't already bought a replacement, buy one now.

  5. Install the replacement battery .

    Push in the new battery facing the same way as the old batteryusually with the numbers facing upor your motherboard won't recognize it. Most battery holders won't let you insert the battery the wrong way.

  6. Close the computer's case .

    Reattach the side panel, if your PC uses one, and then reattach the screws or thumbscrews to hold it in place.

When your PC boots up with a newly installed battery, it may still display confused words about "Setup" or "New Devices." But after automatically identifying its parts once again, the computer memorizes them until the battery dies again, anywhere from 5 to 10 years later.

Replacing a Laptop's Batteries

Unlike PCs, most laptops don't use batteries on their motherboards. However, a laptop's power battery dies after several years of heavy use.

To replace it, push a release latch on your laptop's case, and slide out the battery. Buy a replacement battery from either your laptop's manufacturer or a third-party like FedCo Electronics (

Don't be surprised at the high price. Laptop battery replacements usually cost at least $100.

PCs: The Missing Manual
ISBN: 0596100930
EAN: 2147483647
Year: 2005
Pages: 206
Authors: Andy Rathbone

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