a+ guide to hardware, 4e - south whidbey high school · a+ guide to hardware, 4e. 6. figure 3-4 ....

A+ Guide to Hardware, 4e

Chapter 3Form Factors and Power Supplies

A+ Guide to Hardware, 4e 2

Objectives

• Learn about different form factors and computer cases

• Learn how electricity is measured• Learn how to protect your computer system against

damaging changes in electrical power• Learn about Energy Star specifications• Learn how to troubleshoot electrical problems


Introduction

• Power supply: passes power to PC components• Elements driving type of power supply used in a PC:

– The motherboard– The form factor of the computer case

• Energy Star devices: designed to save energy• Electricity topics covered:

– Measurements of electricity – How electricity is delivered– Protecting a PC from electrical damage– Changing a defective power supply


Computer Case, Motherboard, and Power Supply Form Factors

• Form factor– Specifies size, shape, features of a hardware device

• Form factor for motherboard is chosen first– Same form factor is used for case and power supply

• Using the same form factor assures you that: – The motherboard fits the case– The powers supply cords provide proper voltage– Holes in the motherboard align with holes in the case– Holes in the case align with ports off the motherboard– Wires on the case match connections on motherboard


Types of Form Factors

• AT (Advanced Technology) form factor– Specified motherboard dimensions of 12” x 13.8”– Utilized by IBM AT PC in the 1980s

• Baby AT form factor– Specified motherboard dimensions of 13” x 8.7”– Industry standard form factor from 1993 to 1997

• ATX form factor– Specified motherboard dimensions of 12” x 9.6”– Open specification that is most commonly used today– Includes all AT voltages plus a +3.3-volt circuit


Figure 3-4 The CPU on an ATX motherboard sits opposite the expansion slots and does not block the room needed for long expansion cards


Types of Form Factors (continued)

• MicroATX form factor– Reduces number of I/O slots on the motherboard

• BTX (Balanced Technology Extended) form factor– Focuses on reducing heat and supporting motherboard

• LPX and Mini-LPX form factors– Designed for low-end PC motherboards

• NLX form factor– Developed to improve the LPX form factor

• Backplane Systems (Active and Passive)– Use boards with slots, but little or no circuitry


Figure 3-8 Improved airflow in a BTX case and motherboard makes it unnecessary to have a fan on top of the processor


Types of Cases

• Computer case (chassis)– Houses power supply, motherboard, cards, drives– Panel switches/lights are used to control/monitor PC

• Desktop cases– Motherboard on the bottom, power supply to the rear

• Tower cases– Are up to 2 feet high and can contain several drives

• Notebook cases– Used for all portables and have desktop components


Figure 3-13 Tower and desktop cases


We Need Power!


ATX POWER


MOLEX


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STECKER


Measures and Properties of Electricity

• Successful PC technicians: – Understand electricity– Know how to use electricity – Know how to measure electricity – Can protect computer equipment from electricity

• Units used to measure characteristics of electricity– Volt, amp, ohm, and watt


Table 3-2 Measures of electricity


What are amps, watts, volts and ohms?

• The three most basic units in electricity are • voltage (V), • current (I) • resistance (r). • Voltage is measured in volts• Current is measured in amps • Resistance is measured in ohms.• Electrical power is measured in watts.

http://science.howstuffworks.com/electricity.htm


VOLT V (for example, 110 V)

• V Measures the Potential difference in a circuit • Volts are measured by finding the potential

difference between the pressures on either side of an electrical device in a circuit

• An AT power supply provides four separate voltages:

• +12 V, -12 V, +5 V, and -5 V.• An ATX power supply provides:• +12 V, -12 V, +5 V, -5 V and +3.3 V as well.


Amp or Ampere (1.5A)

• Measures Electrical current• Amps are measured by placing an AMMETER in

the flow of the current. • A 17-inch monitor requires less than 2 A to

operate. • A small laser printer uses about 2 A. • A CD-ROM drive uses about 1 A.


Ohm

• Measures Resistance to electricity• Current can flow in typical computer cables and

wires with a resistance of near zero• Devices are rated according to how much

resistance they offer to electrical current.


WATT (W)

• Measures Electrical Power • Watts measure the total electrical power needed to

operate a device• Watts are calculated by multiplying volts by amps• A computer power supply is rated at 200 to 600 W• While volts and amps are measured to determine

their value, watts are calculated by multiplying voltsby amps.


AC / DC

• Alternating current (AC)– Oscillatory current driven by an alternating voltage– Example: house current oscillates at 60 Hz

• Direct current (DC)– Single direction current driven by constant voltage– Required by computer in small amounts, such as 5 V

• Rectifier: converts AC to DC• Transformer: changes ratio of current to voltage• Power supply acts as a transformer and rectifier


AC and DC

• Electricity can be either AC, alternating current, • or DC, direct current. • Alternating current (AC) cycles, or oscillates,

back and forth rather than traveling in only one direction.

• House current in the United States oscillates 60 times in one second (60 hertz), changing polarity from +110 V to -110 V and causing current to flow in different directions, – depending on whether it’s positive or negative in the

cycle.


AC

• AC is the most economical way to transmit electricity to our homes and workplaces.

• By decreasing current and increasing voltage, we can force alternating current to travel great distances.

• When alternating current reaches its destination, it is made more suitable for driving our electrical devices by decreasing voltage and increasing current.


DC

• Direct current (DC) travels in only one direction and is the type of current that most electronic devices require, including computers.

• A rectifier is a device that converts alternating current to direct current.

• A transformer is a device that changes the ratio of current to voltage.


TRANSFORMERS

• Large transformers reduce the high voltage on power lines coming to your neighborhood to a lower voltage before the current enters your home.

• The transformer does not change the amount of power in this closed system; if it decreases voltage, then it increases current.

• The overall power stays constant, but the ratio of voltage to current changes.


TRANSFORMERS

• A computer power supply changes and conditions the house electrical current in several ways, functioning as both a transformer and a rectifier (see Figure 3-1).

• It steps down the voltage from the 110-volt house current to 3.3, 5, and 12 volts, or to 5 and 12 volts, and changes incoming alternating current to direct current, which the computer and its peripherals require.

• The monitor, however, receives the full 110 volts of AC voltage, converting that current to DC.


DC

• Direct current flows in only one direction, from hot to ground.

• For a PC, a line may be either +5 or -5 volts in one circuit, or +12 or -12 volts in another circuit, depending on whether the circuit is on the positive side or negative side of the power output.

• Several circuits coming from the power supply accommodate different devices with different power requirements.


Figure 3-15 A transformer keeps power constant but changes the ratio of current to voltage


Hot, Neutral, and Ground

• Completing a circuit: – AC travels from power station to house on a hot line– AC travels from panel to device using black (hot) wire– AC flows out of device circuit in a white (neutral) wire – AC returns to power station on a neutral line

• Short circuit: failure due to excess flow of electricity – Fuses protect circuits by melting wire (breaking circuit) – Grounded neutral lines pass detoured AC to earth

• Lines in three-prong plugs: hot, neutral, and ground – Verify wiring of outlet for plug using a receptacle tester


Figure 3-16 Normally, electricity flows from hot to neutral to make a closed circuit in the controlled environment of an electrical device such as a lamp


Figure 3-18 Use a receptacle tester to verify that hot, neutral, and ground are wired correctly

Beware of the different uses of black wire. In PCs, black is used for ground,

but in home wiring, black is used for hot!


Some Common Electric Components

• Materials used to make components:– Conductors: weakly resist flow of current; e.g., copper– Insulators: highly resist flow of current; e.g., ceramics– Semiconductors: allow flow if charged; e.g., silicon

• Transistor– Used to switch current on (1) and off (0)– Also used to amplify current– Made of three layers of semiconductor material– Charge applied to center layer controls switching


Figure 3-19 Symbols for some electronic components and for ground


Some Common Electric Components (continued)

• Capacitor– Holds electrical charge for a period of time– Used to create even flow of current in a PC

• Diode – Allows electricity to flow in one direction only– Used to rectify current (convert AC to DC)

• Resistor– Controls the amount of current flowing through device– Degree of resistance is measured in ohms


Figure 3-20 Capacitors on a motherboard or other circuit board often have embedded crossed lines on top


Protecting Your Computer System

• Electrical threats to a computer system:– Static electricity– Electromagnetic interference – Power surges

• Objectives in this section:– Understand nature of each threat– Learn how to protect your system from these threats


Static Electricity

• Static electricity (electrostatic discharge or ESD)– Due to charge difference between user and device– Touching device causes discharge, damaging device

• ESD is particularly severe in dry and cold climates• How to protect system from ESD:

– Use ground bracelet or ESD gloves– Touch computer case before touching components

• Safety rule: unplug power cord before working in case– Residual power in plugged device can cause damage


EMI (Electromagnetic Interference)

• Caused by magnetic fields generated by current flow• RFI (radio frequency interference):

– EMI in radio frequency range affecting reception• The crosstalk problem

– Data in cables crossing EM fields gets corrupted– Control crosstalk by shielding cables and power supply

• Use a tuned-down AM radio to detect EMI• Other ways to protect a device from EMI:

– Use line conditioners to filter out electrical noise– Move the PC to a new location


Surge Protection and Battery Backup

• Storms and uneven AC flow cause power surges• Prevent power surges by installing an AC filter• Types of devices used to manage power surges:

– Surge suppressors– Power conditioners– Uninterruptible power supplies (UPSs)

• Use devices with UL (Underwriters Laboratory) logo


Surge Suppressors

• Also called a surge protector• Protects equipment from sudden changes in power

– Works by absorbing and/or blocking the surge • Recommended features:

– Joules rating that is greater than 600 joules– Protection activated in less than 2 nanoseconds– Warranty for connected equipment and UL seal– Light indicating that surge protection is working– Data line protector for telephone line to modem– Let-through voltage rating and line noise filtering


Figure 3-21 This surge suppressor has six electrical outlets, two phone jacks, and a power protection light


Power Conditioners

• Sometimes called line conditioners• Functions:

– Protect against spikes or swells (voltage surges)– Raise voltage during brownouts (voltage sags)

• Load supported measured in watts or volt-amps (VA)• Determining the VA needed to support your system:

– Multiply the amperage of each component by 120 V– Add up the VA for each component


Uninterruptible Power Supply

• UPS offers three benefits:– Conditions line to account for brownouts and spikes– Provides power backup when AC fails (blackout)– Provides protection against very high spikes

• Designs: standby, inline, and line-interactive• Smart (intelligent) UPS: controlled with software• What to consider when buying a UPS:

– UPS rating should exceed VA load by at least 25 %– Degree of line conditioning– Warranties, guarantees, and service policies


Energy Star Systems (The Green Star)

• Energy Star systems have the U.S. Green Star – Indicates device meets energy conserving standards– Devices: computers, monitors, printers, copiers, faxes

• Goals of Energy Star (a.k.a. Green) standards:– Reduce overall electricity consumption– Protect and preserve natural resources

• How computer components meet standards– Uses standby program for switching to sleep mode – No more than 30 watts used during sleep mode


Power-Management Methods and Features

• Methods used to meet Energy Star standards:– Advanced Configuration and Power Interface (ACPI)

• Standard used by most desktops and notebooks• Comprises four power-saving modes: S1 - S4 • Some features controlled by BIOS, others by Windows

– Advanced Power Management (APM) specification– AT Attachment (ATA) for various drives– Display Power Management Signaling (DPMS)


Figure 3-24 A power management BIOS setup screen showing power-management features


Energy Star Monitors

• Display Power Management Signaling (DPMS)– Specifications applying to video card and monitor– Allow both devices to simultaneously enter sleep mode

• Accessing energy settings in Windows 2000/XP– Right-click the desktop and select Properties

• The Display Properties dialog box opens– Click the Screen Saver tab

• If monitor is Energy Star–compliant, logo is at bottom– Click Power button to open Power Options Properties


Figure 3-25 Changing power options in Windows XP


Troubleshooting the Electrical System

• Problems can occur before or after boot• Problems can be consistent or inconsistent• Possible symptoms of an electrical problem:

– The PC appears “dead”– The PC sometimes halts during booting– Error codes or beeps occur during booting– You smell burnt parts or odors

• Check the simple things first– Example: determine whether all switches are on


Problems with External Power

• Brownout (reduced current) may create issues– Check out other devices using the same circuit– Remove other devices to see if voltage increases

• Dealing with intermittent errors caused by noise:– Use a line monitor to monitor and condition voltage


Problems with Loose Internal Connections

• Can cause a system to appear dead or reboot itself• Troubleshooting tasks:

– Remove the cover of the case– Check all power connections

• Check cables linking power supply to motherboard• Check cables linking power supply to drives


Figure 3-26 For an ATX or BTX power supply, the remote switch wire must be connected to the motherboard before power will come on


Problems that Come and Go

• Intermittent symptoms indicating a post-boot problem– The computer stops or hangs or reboots for no reason– Memory errors appear intermittently– Data is written incorrectly to the hard drive– The keyboard stops working at odd times– The motherboard fails or is damaged– Power supply overheats and becomes hot to the touch– The power supply fan becomes very noisy or stops

• Intermittent problems are often difficult to solve


Problems with an Inadequate Power Supply

• Power supply may not meet needs of new devices • Testing for an adequate power supply

– Make all devices in the system work at the same time– Example: copy files from new drive to old drive

• Simple solution: upgrade to a higher power supply• Calculating total wattage needed by system

– Multiply volts in circuit by amps required for device– Add all products to determine total wattage

• Power supply range: 200 watts to 600 watts


Problems with the Power Supply, Boards, or Drives

• Issues:– Inadequate or faulty power supply – Components drawing power might be bad

• Problems caused:– System hangs or gives intermittent errors– System reboots or does not boot at all

• Actions to take: – Isolate and remove any faulty expansion cards – Upgrade or switch the power supply – Test voltage output of power supply with a multimeter


Problems with the Power Supply Fan

• Defective fans usually hum before they stop working• Response to diagnosis of defective fan

– Replace fan or the entire power supply• If replacement does not work, suspect another short• Do not operate a PC if the fan does not work

– Computers will overheat, damaging circuit boards• Indirect sources of fan problems:

– Shorts in drives, motherboard, or expansion cards


Power Problems with the Motherboard

• Bad contact between board component and chassis– Short can seriously damage the motherboard– Check for missing or extra standoffs (spacers)

• Shorts in the circuit on the motherboard– Look for damage to the bottom of the motherboard– Look for burned-out capacitors

• Frayed wires on connections can also cause shorts– Test hard drive cables connected to motherboard


Problems with Overheating

• Causes intermittent problems • May also cause the system to reboot or not boot• Temperature in a case should not exceed 100° F• Some possible solutions:

– Remove dust from power supply, vents, heat sink– Secure cables and cords with tie wraps– Install another exhaust fan on the rear of the case– Install a fan in expansion slot next to video card– Replace component that is damaged


Figure 3-27 Install one exhaust fan on the rear of the case to help pull air through the case


Replacing the Power Supply

• The power supply is a field replaceable unit (FRU)• Criteria for replacement power supply to meet:

– Uses the correct form factor– Adequately rated for power in watts– Has all power connectors needed by your system

• Before replacing power supply, test new device– Connect components to new power supply– Turn on PC and observe whether problem is solved– If problem is solved, perform replacement procedure


Summary

• Form factor: specifies size, shape, features of device• Motherboard, power supply, and case share the same

form factor, such as ATX • Three types of cases: desktop, tower, and notebook• Quantities that characterize electricity: voltage,

current, resistance, and power• Current flows from hot wires to neutral wires; excess

current escapes through grounds


Summary (continued)

• AC supplied by power station is transformed and rectified before flowing into the PC

• Major components in a circuit board: transistor, capacitor, diode, resistor

• Electrical threats: ESD, EMI, uneven current flow, sudden power surges (or spikes)

• Energy Star standards promote energy conservation• PCs comply with Energy Star standards by enabling

devices to enter into a low power sleep mode

a+ guide to hardware, 4e - south whidbey high school · a+ guide to hardware, 4e. 6. figure 3-4 ....

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