a+ guide to managing and maintaining your pc, 6e chapter 4 form factors and power supplies (v0.1)

A+ Guide to Managing and Maintaining your PC, 6e

Chapter 4Form Factors and Power Supplies (v0.1)

A+ Guide to Managing and Maintaining your PC, 6e 2

Computer Case, Motherboard, and Power Supply Form Factors

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

such as a motherboard• 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


Motherboard Form Factor

• 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


Baby AT Motherboard


Figure 4-4 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 4-8 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 4-13 Tower and desktop cases


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


Materials

• Conductor - allows the flow of electricity– Examples: copper, aluminum

• Insulator - resists the flow of electricity– Examples: plastic, rubber, glass

• Semiconductor - between an insulator and a conductor– Examples: silicon, germanium


Basic Electrical Units

• Voltage

• Current

• Resistance (Impedance)

• Power


Voltage

• Potential difference also called a difference in charge

• Measured in units called volts


Current

• Volume or number of electrons that flow through an electrical system

• Measured in units called amperes or amps


Resistance

• Opposes the flow of electrical current

• As resistance in an circuit increases the current that flows decreases

• Measured in ohms


Relationship

• Given a constant resistance as the voltage in an electrical circuit increases so does the current flow


Ohm’s Law

• Relationship between voltage, current, and resistance in an electrical circuit


Ohm’s Law Equation

• I = E / R– I is the current in amps– E is the voltage in volts– R is the resistance in ohms


Power

• Energy needed to operate an electrical device

• Important because it produces heat as a result

• Measured in units called watts


Calculation of Power

• P = E x I – P is the power in watts– E is the voltage in volts– I is the current in amps


Table 4-2 Measures of electricity


AC and DC

• Alternating current (AC)– Voltage changes with time (frequency)– In USA the AC line frequency is 60 Hz

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


Electrical Components

• Rectifier– converts AC to DC

• Transformer– Changes voltage– Step up (increases voltage)– Step down (decreases voltage)

• Power supply– Has functions of a transformer and rectifier


Figure 4-15 A transformer keeps power constant but changes the ratio of current to voltage (This is an example of a step down transformer)


Common Household Wiring

• 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

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


Figure 4-16 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 4-18 Use a receptacle tester to verify that hot, neutral, and ground are wired correctly


Split Phase Power (US)


Line Fault Conditions

• Short circuit– failure due to an uncontrolled excess flow

of electricity

• Fuses protect circuits by melting wire (breaking circuit)

• Grounded neutral lines pass detoured AC to earth


Some Common Electric Components

• 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


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 4-19 Symbols for some electronic components and for ground


Figure 4-20 Capacitors on a motherboard or other circuit board often have embedded crossed lines on top


Protecting Computer Systems


Protecting Your Computer System

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


Static Electricity

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

• ESD voltages as low as 10 V can can cause problems

• Walking across a carpet can generate up to 12,000 volts

• ESD is particularly severe in dry and cold climates


Protection from ESD

• How to protect system from ESD– Use ground bracelet or ESD gloves– Anti-static carpeting or floor matts– Touch computer case before touching components

• Safety rule: unplug power cord before working in case– Eliminate potential electrical shock hazard– Residual power in plugged device can cause

damage


EMI (Electromagnetic Interference)

• Caused by magnetic fields which are generated by electrical current flow

• The crosstalk is an example of EMI– Data in cables crossing EM fields gets corrupted

• RFI (radio frequency interference)– Cause by close proximity to a source of RF

• Arc welders

– EMI in radio frequency range affecting reception


Detecting and Preventing EMI

• Use a tuned-down AM radio to detect EMI

• Control crosstalk by shielding cables and power supply

• Use line conditioners to filter out electrical noise

• Move the PC to a new location


Surge Protection

• Sudden changes in voltage to beyond the tolerance of the electrical equipment– +/- 10% of voltage (120V)

• Storms and uneven AC flow cause power surges– Sudden changes in voltage


Surge Protection (continued)

• Types of devices used to manage power surges– Surge suppressors– Power conditioners– Uninterruptible power supplies (UPS’s)

• Use devices with UL (Underwriters Laboratory) logo (UL 1449)


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 4-21 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 4-24 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 4-25 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 4-26 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 4-27 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 managing and maintaining your pc, 6e chapter 4 form factors and power supplies (v0.1)

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