Power Supply

Question 1

Power Supply or PSU, for power supply unit (for an exam)

Answer 1

that takes electricity from the wall socket and transforms it into electricity to run the motherboard and other internal components. All of the wires dangling out of it connect to the motherboard and peripherals.

Question 2

Field replaceable unit (FRU)

Answer 2

refers to the typical parts a tech should carry, such as RAM and a hard drive.

Question 3

Ground wire

Answer 3

An electrical outlet must be grounded (that is, have a ground wire) have a ground wire to be suitable for PC use. You can tell a grounded outlet because it has a small round hole in addition to the two flat ones. More on this in the next chapter.

Question 4

direct current (DC)

Answer 4

in which the electrons flow in one direction around a continuous circuit

Question 5

alternating current (AC)

Answer 5

in which the flow of electrons alternates direction back and forth in a circuit.

Question 6

USA voltages

Answer 6

standard AC comes in somewhere between 110 and 120 V, often written as ~115 VAC (volts of alternating current)

Question 7

Rest of the world

Answer 7

220–240 VAC, so power supplies are available with dual-voltage options, making them compatible with either standard.

Question 8

dual-voltage options

Answer 8

making them compatible with either standard (115 or 240) volts

Question 9

IEC-320 connector.

Answer 9

The power supply connects to the power cord (and thus to an electrical outlet) via a standard IEC-320 connector.

Question 10

testing AC power,

Answer 10

check for three things: hot to neutral (115V), hot to ground (115V, and neutral to ground (0V).

Question 11

multimeter often reffered to as volt-ohm meter (VOM) or digital multimeter (DMM)

Answer 11

to measure a number of aspects of electrical current. A multimeter consists of two probes, an analog or digital meter, and a dial to set the type of test you want to perform.

Question 12

Multimeter symbol

Answer 12

Note that some multimeters use symbols rather than letters to describe AC and DC settings. The V with the solid line above a dashed line refers to direct current. The V~ stands for alternating current.

Question 13

four types of electrical tests:

Answer 13

continuity, resistance, AC voltage (VAC), and DC voltage (VDC)

Question 14

Continuity

Answer 14

tests whether electrons can flow from one end of a wire to the other end. If so, you have continuity; if not, you don’t. You can use this setting to determine if a fuse is good or to check for breaks in wires. If your multimeter doesn’t have a continuity tester (many cheaper multimeters do not), you can use the resistance tester. A broken wire or fuse will show infinite resistance, while a good wire or fuse will show no resistance. Testing AC and DC voltages is a matter of making sure the measured voltage is what it should be.

Question 15

Using a Multimeter to Test AC Outlets

Answer 15

Move the selector switch to the AC V (usually red). If multiple settings are available, put it into the first scale higher than 120 V (usually 200 V). Auto-range meters set their own range; they don’t need any selection except AC V.
Place the black lead in the common hole. This is for ground and is often marked with a minus sign (–) or COM. If the black lead is permanently attached, ignore this step.
Place the red lead in the V-Ohm-A hole. This is often marked with a plus sign (+). If the red lead is permanently attached, ignore this step.

Put either lead in hot, the other in neutral. You should read 110 to 120 V AC.
Put either lead in hot, the other in ground. You should read 110 to 120 V AC.
Put either lead in neutral, the other in ground. You should read 0 V AC.
If any of these readings is different from what is described here, it’s time to call an electrician.

Question 16

polarity

Answer 16

(which wire is hot and which is neutral)

Question 17

brownouts

Answer 17

Large sags in electricity are also known as brownouts

Question 18

blackout

Answer 18

When the power cuts out completely, it’s called a blackout.

Question 19

Sag

Answer 19

power company tends to drop well below (sag)

Question 20

surge or spike

Answer 20

shoot far above (surge or spike) the standard 115 V (in the United States).

Question 21

surge suppressor

Answer 21

Given the seriousness of surges, every PC should use a surge suppressor device that absorbs the extra voltage from a surge to protect the PC. A dedicated surge suppressor works between the power supply and the outlet to protect the system from power surges, extending the life of the power supply.

Make sure your surge suppressor has the Underwriters Laboratories UL 1449 for 330-V rating to ensure substantial protection for your system. Underwriters Laboratories (www.ul.com) is a U.S.-based, not-for-profit, widely recognized industry testing laboratory whose testing standards are very important to the consumer electronics industry.

Question 22

joule

Answer 22

A joule is a unit of electrical energy. How much energy a surge suppressor can handle before it fails is described in joules. Most authorities agree that your surge suppressor should rate at a minimum of 2,000 joules—and the more joules, the better the protection.

Question 23

clamping voltage

Answer 23

Surge suppressors are also rated in clamping voltage, in which an overvoltage condition is “clamped” to a more manageable voltage for a certain amount of time. Good consumer suppressors can clamp 600 volts down to 180 volts or less for at least 50 microseconds and can do so on either the hot line or neutral line.

Question 24

Note

Answer 24

Caution: No surge suppressor in the world can handle the ultimate surge, the electrical discharge of a lightning strike. If your electrical system takes such a hit, you can kiss your PC and any other electronic devices goodbye if they were plugged in at the time. Always unplug electronics during electrical storms!

Question 25

Note 1

Answer 25

No surge suppressor works forever. Make sure your surge suppressor has a test/reset button so you’ll know when the device has—as we say in the business—turned into an extension cord. If your system takes a hit and you have a surge suppressor, call the company! Many companies provide cash guarantees against system failure due to surges, but only if you follow their guidelines.

Question 26

superior surge suppressors

Answer 26

add power conditioning to filter out EMI electromagnetic interference and RFI radio frequency interference. occasionally events (such as nearby lightning) generate enough line noise to cause weird things to happen to your PC (keyboard lockups, messed-up data).

Question 27

uninterruptible power supply (UPS)

Answer 27

protects your computer (and, more important, your data) in the event of a power sag or power outage. A UPS essentially contains a big battery that provides AC power to your computer regardless of the amount of power coming from the AC outlet. All uninterruptible power supplies are measured in both watts (the true amount of power they supply in the event of a power outage) and in volt-amps (VA)

Question 28

volt-amps (VA)

Answer 28

A UPS provides perfect AC power, moving current smoothly back and forth 60 times a second (or 50 in other parts of the world). The volt-amps rating describes the amount of power the UPS could supply if the connected devices took power from the UPS perfectly. Power supplies, monitors, and other devices, however, may not take all of the power the UPS has to offer at every point as the AC power moves back and forth, resulting in inefficiencies. If your devices took all of the power the UPS offered at every point as the power moved back and forth, VA would equal watts.

Question 29

UPS

Answer 29

If the UPS makers knew ahead of time exactly what devices you planned to plug into their UPS, they could tell you the exact watts, but different devices have different efficiencies, forcing the UPS makers to go by what they can offer (VAs), not what your devices will take (watts). The watts value they give is a guess, and it’s never as high as the VAs. The VA rating is always higher than the watt rating.

Question 30

two main types of UPS

Answer 30

nline, where devices are constantly powered through the UPS’s battery, and standby, where devices connected to the UPS receive battery power only when the AC sags below ~80–90 V. nline, where devices are constantly powered through the UPS’s battery, and standby, where devices connected to the UPS receive battery power only when the AC sags below ~80–90 V. Every UPS also has surge suppression and power conditioning, so look for the joule and UL 1449 ratings. Also look for replacement battery costs—some UPS replacement batteries are very expensive. Last, look for a UPS with a USB port. This port enables you to connect the UPS to a computer and use software to monitor the UPS’s status and read its event logs.

Question 31

Power Supply Unit

Answer 31

, the power supply unit (PSU) takes over, converting high-voltage AC into several DC voltages (notably, 5.0, 12.0, and 3.3 V) usable by the delicate interior components. Power supplies come in a large number of shapes and sizes, but the most common size by far is the standard 150 mm × 140 mm × 86 mm desktop PSU shown below.

Question 32

PSU wires

Answer 32

The PC uses the 12.0-V current for most things on modern systems, with voltage regulator modules converting the voltage and current to match the needs of the various components. The 5.0-V and 3.3-V currents power some logic boards and circuits. Power supplies also come with standard connectors for the motherboard and interior devices such as disk drives. The wire colors are significant. For example, black wires are for grounding, yellow wires are for +12 V, and red wires are for +5 V. \

Question 33

Power to the Motherboard

Answer 33

Motherboards use a 20- or 24-pin P1 power connector. Some motherboards may require special 4-, 6-, or 8-pin connectors to supply extra power.

Question 34

Power supply to peripherals: Molex and SATA

Answer 34

The typical PC power supply has up to two types of connectors that plug directly into peripherals: Molex and SATA. There used to be a third type, mini, that plugged into floppy drives, but it’s obsolete now.

Question 35

Molex connectors

Answer 35

The Molex connector supplies 5-V and 12-V current for fans and older drives. The Molex connector has notches, called chamfers, that guide its installation.

Question 36

SATA Power Connectors

Answer 36

Serial ATA (SATA) drives use a 15-pin SATA power connector. The larger pin count supports the SATA hot-swappable feature and 3.3-, 5.0-, and 12.0-V devices. The 3.3-V pins are not used in any current SATA drives but are reserved for possible future use. All generations of SATA use the same power connectors. almost impossible to insert one incorrectly into a SATA drive. They are usually black.No other devices on your computer uses the SATA power connector. an interface for connecting a host bus adapter to a mass storage device or optical drive

Question 37

Splitters and Adapters

Answer 37

You may occasionally find yourself without enough connectors to power all of the devices inside your PC. In this case, you can purchase splitters to create more connections. You might also run into the phenomenon of needing a SATA connector but having only a spare Molex. Because the voltages on the wires are the same, a simple adapter will take care of that problem nicely.

Question 38

Soft Power

Answer 38

The power switch on an ATX system simply sends a signal to the motherboard that it should start up the system. The BIOS or operating system takes over from there and handles the chore of turning the PC on or off. This is called soft power.

Question 39

ATX standards

Answer 39

ATX did a great job supplying power for more than a decade, but over time more powerful CPUs, multiple CPUs, video cards, and other components began to need more current than the original ATX provided. This motivated the industry to introduce a number of updates to the ATX power standards: ATX12V 1.3, EPS12V, multiple 12-V rails, ATX12V 2.0, other form factors, and active PFC.

Question 40

ATX

Answer 40

Advanced Technology eXtended (ATX) is a specification that applies to motherboards, cases, and power supplies. They all work together and must be jointly compatible, as you learned in Lesson 4. ATX was developed several decades ago as an improvement on the original Advanced Technology (AT) standard. ATX power supplies have two distinguishing physical features that improve upon AT: the motherboard power connector and soft power. Motherboard power for ATX comes from a single cable with a 20-pin P1 motherboard power connector. ATX power supplies also have at least two other cables, each populated with two or more Molex or mini connectors for peripheral power.

Question 41

ATX12V 1.3

Answer 41

The first widespread update to the ATX standard, ATX12V 1.3, came out in 2003. This introduced a 4-pin motherboard power connector, unofficially but commonly called the P4, that provided more 12-V power to assist the 20-pin P1 motherboard power connector. All power supplies—assuming they have a P4 connector—are ATX12V or one of the later standards.

Question 42

SATA (exam tip)

Answer 42

SATA also supports a slimline connector that has a 6-pin power segment and a micro connector that has a 9-pin power segment.

Question 43

EPS12V

Answer 43

ATX12V 1.3 power supplies worked fine for consumer systems but didn’t offer enough power for some server motherboards. To address server needs, an industry group called the Server System Infrastructure (SSI) developed a non-ATX standard motherboard and power supply called EPS12V.

Question 44

EPS12V

Answer 44

An EPS12V power supply comes with a 24-pin main motherboard power connector that resembles a 20-pin ATX connector, but that offers more current and thus more stability for motherboards. It also comes with an AUX connector, an ATX12V P4 connector, and a unique 8-pin connector. That’s a lot of connectors! EPS12V power supplies are not interchangeable with ATX12V power supplies.

Question 45

Multiple 12-V Rails

Answer 45

A rail is a set of wires (traces) in the power supply circuit board. A traditional power supply had one rail for each voltage provided, though the only one that concerns us here is the 12-V rail. That’s the one that does most of the work on modern systems.

Each rail is monitored by a circuit called an over current protection (OCP). The OCP monitors the rail so it can shut the power supply down if too much current goes through the rail. In a single-rail system, a single OCP monitors all the pathways. In a multi-rail system, each pathway gets its own OCP.

Question 46

Rail

Answer 46

A rail is a set of wires (traces) in the power supply circuit board. A traditional power supply had one rail for each voltage provided, though the only one that concerns us here is the 12-V rail.

Question 47

over current protection (OCP)

Answer 47

Each rail is monitored by a circuit called an over current protection (OCP). The OCP monitors the rail so it can shut the power supply down if too much current goes through the rail. In a single-rail system, a single OCP monitors all the pathways. In a multi-rail system, each pathway gets its own OCP.

Question 48

ATX12V 2.0

Answer 48

The ATX12V 2.0 standard incorporates many of the good ideas of EPS12V into the ATX world, starting with the 24-pin connector. This 24-pin motherboard power connector is backward compatible with the older 20-pin connector, so users don’t have to buy a new motherboard if they use an ATX12V 2.0 power supply. ATX12V 2.0 requires two 12-V rails for any power supply rated higher than 230 W. ATX12V 2.0 drops the AUX connector and requires SATA hard drive connectors.

Many modern ATX motherboards feature an 8-pin CPU power connector, like the one found in the EPS12V standard, to help support high-end CPUs. This connector is referred to by several names, including EPS12V, EATX12V, and ATX12V 2x4. One half of this connector will be pin compatible with the P4 power connector, and the other half may be under a protective cap. Be sure to check the motherboard installation manuals for recommendations about if and when you need to use the full 8 pins. For backward compatibility, some power supplies provide an 8-pin power connector that can split into two 4-pin sets, one of which is the P4 connector.

Question 49

24-pin P1 (exam tip)

Answer 49

The ATX 24-pin power supply connector is the standard motherboard power connector in computers today.

The connector itself is a Molex 39-01-2240 connector, often called a Molex Mini-fit Jr.

Question 50

ATX12 2.0

Answer 50

Another notable connector is the auxiliary PCI Express (PCIe) power connector. Some motherboards add a Molex socket for PCIe, and some video and sound cards come with a Molex socket as well. Higher-end cards have a dedicated 6-pin or 8-pin PCIe power connector, sometimes even two of them. The 8-pin PCIe connector should not be confused with the EPS12V connector, as they are not compatible. Often you’ll find that 8-pin PCIe power cables have two pins at the end that you can detach for easy compatibility with 6-pin devices.

Question 51

harmonics

Answer 51

A PC’s power supply, simply due to the process of changing this AC current into DC current, is like a person sucking on a straw on the end of this pipe. It takes gulps only when the current is fully pushing or pulling at the top and bottom of each cycle and creating an electrical phenomena—sort of a back pressure—that’s called harmonics in the power industry. These harmonics create the humming sound you hear from electrical components.

Question 52

active power factor correction (active PFC)

Answer 52

Good PC power supplies come with active power factor correction (active PFC), extra circuitry that smoothes out power coming from the wall before passing it to the main power supply circuits. This smoothing process eliminates any harmonics. Never buy a power supply that does not have active PFC—all power supplies with active PFC will announce it on the box.

Question 53

Power Supply required watts

Answer 53

500 watts and with four standard screws

Question 54

ATX power supply never turns off when plugged in

Answer 54

5V As long as that power supply stays connected to a power outlet, the power supply will continue to supply 5 V to the motherboard.

Question 55

shorting the pins

Answer 55

One trick when in that situation is to use a set of car keys or a screwdriver to create an electrical connection between the two pins that the power button’s connector would attach to on the motherboard. This is called shorting the pinsand it has the same effect as pressing the power button. Check the motherboard manual to figure out which pins.

Question 56

Power Supply fan

Answer 56

If you ever turn on a computer and it boots just fine but you notice that it seems unusually quiet, check to see if the power supply fan has died. If it has, quickly turn off the PC and replace the power supply.

Question 57

slot covers

Answer 57

Also, make sure that expansion bay slots in the back of the case have small metal covers—called slot covers. Slot covers assist in maintaining a steady airflow. Plus, they also help keep dust out of your case. Exam Tip: Missing slot covers can cause the PC to overheat!

Question 58

modular power supply

Answer 58

A modular power supply doesn’t have fixed power cables for devices and the motherboard. Rather, it has multiple sockets. On the other hand, some techs claim that modular cables hurt efficiency because the modular connectors add resistance to the lines. You make the choice: Is a slight reduction in efficiency worth a clean look?

Question 59

Troubleshooting Power Supplies

Answer 59

Power supplies fail in two ways: sudden death and slowly over time. When they die suddenly, the computer will not start and the fan in the power supply will not turn. In this case, verify that electricity is getting to the power supply before you do anything.

Question 60

Power supply troubleshooting

Answer 60

Do not panic if your power supply puts out slightly more or less voltage than its expected values. The voltages supplied by most PC power supplies can safely vary by as much as ±10% of their stated values. This means that the 12.0-V line can vary from roughly 10.8 to 13.2 V without exceeding the tolerance of the various systems in the PC. The 5.0- and 3.3-V lines offer similar tolerances.

Question 61

ATX tester

Answer 61

Power supplies will not start unless they’re connected to a motherboard, so what do you do if you don’t have a motherboard you trust to test? First, try an ATX tester, a little box with typical power sockets and an on/off switch. Many companies make these devices. Look for one that supports both 20- and 24-pin motherboard connectors as well as all of the other connectors on your power supply.

Question 62

Power Supply dying (intermittent)

Answer 62

The secret to discovering that a power supply is dying lies in one word: intermittent. Whenever you experience intermittent problems, your first guess should be that the power supply is bad. Here are some other clues you may hear from users:

“Whenever I start my computer in the morning, it starts to boot, and then locks up. If I press CTRL + ALT + DEL two or three times, it will boot up fine.”
“Sometimes when I start my PC, I get an error code. If I reboot, it goes away. Sometimes I get different errors.”
“My computer will run fine for an hour or so. Then it locks up, sometimes once or twice an hour.”

Sometimes something bad happens and sometimes it does not. That’s the clue for replacing the power supply. And don’t bother with the multimeter; the voltages will show up within tolerances, but only once in a while they will spike and sag (far more quickly than your multimeter can measure) and cause these intermittent errors. When in doubt, change the power supply.

Question 63

A halon fire extinguisher

Answer 63

A halon fire extinguisher will also work for electronics. Halon is a gas that becomes liquified under compression. The advantage of a halon fire extinguisher is that it doesn’t leave messy residue behind when it sprays. It also has very low toxicity so it’s safe for human exposure. Great, huh? Exam Tip: If your power supply is smoking or you smell something burning inside of it, stop using it now. Replace it with a new power supply.

Question 64

Temperature and Efficiency

Answer 64

Watch out for power supplies that list their operating temperature at 25º C—about room temperature. A power supply that provides 500 W at 25º C will supply substantially less in warmer temperatures, and the inside of your PC is usually 15º C warmer than the outside air. Sadly, many power supply makers—even those who make good power supplies—fudge this fact.