Transcript Measuring Voltage of a Power Supply

Chapter 3
Electricity and
Power Supplies
You Will Learn…
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How electricity is measured
How to protect your computer system from damaging
changes in electrical power
About types of form factors and computer cases
How to detect and correct power supply problems
About Energy Start specifications
Electricity: A Basic Introduction
The Properties of Electricity
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The Properties of Electricity
Measuring Voltage with a Voltmeter
Measuring Amps with an Ammeter
Relationship Between Voltage and
Current
• Direct relationship
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As electrical potential difference (or voltage)
increases, electrical current increases
 As voltage decreases, current decreases
Relationships Among Voltage,
Current, and Resistance
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Voltage and current have a direct relationship
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Resistance has an inverse relationship with voltage
and current
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When voltage increases, current increases
As resistance increases, either current or voltage decreases
As resistance decreases, either current or voltage increases
(Ohm’s Law)
One volt drives a current of one amp through a
resistance of one ohm
AC (Alternating Current)
• Cycles or oscillates back and forth rather than
traveling in one direction
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60 times in one second (60 hertz)
• Most economical way to transmit electricity to
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homes and workplaces
Can be forced to travel great distances by
decreasing current and increasing voltage
DC (Direct Current)
• Travels in only one direction
• Required by most electronic devices, including
a computer (power supply acts as both a
rectifier and a transformer)
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Rectifier converts AC to DC
 Transformer
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Changes the ratio of current to voltage
Overall power stays constant
Computer Power Supply
Hot, Neutral, and Ground
Hot, Neutral, and Ground
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Short circuit occurs when
electricity is allowed to flow
uncontrolled from hot line to
neutral line or from hot line
to the ground
Fuses prevent too much
current from flowing
through the circuit
Neutral line to a house is
grounded many times along
the way and at breaker box
Hot, Neutral, and Ground
Common Electrical Components
• Transistors
• Capacitors
• Diodes
• Ground
• Resistors
Materials Used to Make Electrical
Components
• Conductors
• Insulators
• Semiconductors
Transistor
• Electronic device that can serve as a gate or
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switch for an electrical signal
Can amplify flow of electricity
Made of three layers of semiconductor material
Basic building block of an integrated circuit
(IC) that is used to build a microchip
Capacitor
• Can hold an electrical charge
• Smoothes out uneven flow of electricity
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through a circuit
Maintains a charge long after current is no
longer present
Diodes and Resistors
• Diode
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Semiconductor device that allows electricity to
flow in only one direction
• Resistor
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Electronic device that limits amount of current that
can flow through it
Protecting Your Computer System:
General Precautions
• Make notes so you can backtrack
• Remove packing tape and cellophane from
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work area
Keep components away from hair and clothing
Keep screws and spacers in an orderly place
Don’t stack boards on top of each other
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Protecting Your Computer System:
General Precautions
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Don’t touch chips on motherboard or expansion cards
Don’t touch a chip with a magnetized screwdriver
Don’t use a graphite pencil to change DIP switch
settings
Turn off a computer before moving it
Keep disks away from magnetic fields, heat, and
extreme cold
Protecting Against Electricity
• Turn off power and unplug computer
• Use a ground bracelet
• Never touch inside of a computer while it is
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turned on
Never remove cover or put your hands inside
monitor or power supply
Static Electricity
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Electrostatic discharge (ESD)
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Electrical charge at rest
Brief flow of electricity caused by contact between two
objects that had a difference in voltage potential
Can cause catastrophic or upset failure
Static control devices or methods:
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Ground bracelet or static strap (except when working inside
a monitor or with high-voltage equipment)
Ground mats
Static shielding bags
Ground Bracelet
Ground Mat
Static Shielding Bags
EMI (Electromagnetic Interference)
• Caused by the magnetic field produced as a
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side effect when electricity flows
Radio frequency interference (RFI) can cause
problems with radio and TV reception
Use a line conditioner to filter electrical noise
causing the EMI
Surge Protection
and Battery Backup
• Devices that control electricity to a computer
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Surge suppressors (surge protectors)
 Power conditioners
 Uninterruptible power supplies (UPSs)
• Should have UL (Underwriters Laboratory)
logo
Surge Suppressors
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Protect equipment against sudden changes in level of
power
Shunt type, series type, or combination
Can come as power strips, wall-mounted units that
plug into AC outlets, or consoles; some provide RJ-11
telephone jack to protect modems and fax machines
Data line protector (for phone line)
Power Conditioners and UPSs
• Provide protection against spikes
• Regulate (condition) the power, providing
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continuous voltage during brownouts
Sometimes called line conditioners
Uninterruptible Power Supply
• Benefits
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Conditions line for brownouts and spikes
 Provides backup power during a blackout
 Protects against very high potentially damaging spikes
• Types
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Standby device
 Inline device
 Line-interactive device
Uninterruptible Power Supply
Uninterruptible Power Supply
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Intelligent UPS
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Can be controlled and managed from utility software at a
remote computer
Must have a serial port connection to PC and a
microprocessor on board
What to consider when buying a UPS
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Cost
 UPS rating should exceed total VA or wattage output by at
least 25%
 Be aware of degree of line conditioning
 Consider warranty, service policies, and guarantee
UPS Manufacturers
The Computer Case
and Form Factors
• Form factor
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Description of size, shape, and general makeup of a
hardware component
 Use same form factor for motherboard, case, and
power supply
Case, Power Supply, and
Motherboard Form Factors
• XT (older, outdated) • Most common form
factors used on PCs:
• AT
 AT
• ATX (most popular)
 Baby AT
• LPX
 ATX
• NLX
 Mini-ATX
• Backplane systems
AT Form Factor
• Used on older motherboards
• Uses full-size AT cases used by original IBM
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AT personal computer
Cannot be used with smaller AT cases or with
newer ATX cases
Difficult to install, service, and upgrade
No longer produced by most manufacturers
AT Motherboard
Baby AT
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Industry standard from 1993-1997 because of greater
flexibility
Power supplies blow air out of computer case
Smaller motherboards fit into many types of cases
Problematic position of CPU in relation to expansion
slots not resolved
Cables might not be long enough
ATX
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Superseded earlier AT and Baby AT form factors
Open, nonproprietary industry specification
developed by Intel in 1995
Easier to add and remove components
Greater support for I/O devices and processor
technology
Lower costs
Better positioning of components on motherboard
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ATX
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Possible to reduce cable lengths, which can help
reduce potential for EMI and corrupted data
Power supply and motherboard use single power
connector (P1 connector)
Power supply fan blows air into case; cools processor
directly
Soft switch feature
Other types of ATX boards (Mini-ATX, MicroATX,
FlexATX )
ATX Motherboard
LPX and Mini LPX
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Developed by Western Digital
Often used in low-cost systems
Expansion cards mounted on riser card that plugs into
motherboard
Not easy to upgrade
Cannot handle physical size of recently developed processors
Not designed to handle higher temperature at which faster
processors operate
Use low profile cases and slim-line cases
LPX
NLX
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For low-end PC motherboards
Use low-profile cases
Provide greater support for current and up-andcoming processor technologies
Flexible; use space efficiently
NLX
Backplane Systems
• Do not use a true motherboard, but a board that
normally sits against back of a proprietary case
that has slots for other cards
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Active backplanes
 Passive backplanes
• Not generally used in PCs
Types of Cases
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Computer case (chassis)
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Houses power supply, motherboard, expansion cards, drives
Lights and switches on front panel for controlling and
monitoring PC
Needs to fit its intended use
Major categories
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Desktop cases
Tower cases
Notebook cases
Desktop Cases
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Classic case with four drive bays and six expansion
slots; sits on desktop and does double duty as a
monitor stand
Being replaced by smaller and more space-efficient
cases
For low-end desktop systems, compact cases follow
either the NLX, LPX, or Mini-LPX form factor
A Desktop Case
Tower Cases
• Provide maximum space for working inside a
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computer and moving components around
Variations
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Minitower
 Midsize tower (most popular)
 Full-size tower
Minitower
Tower and Desktop Cases
Notebook Cases
• Used for portable computers that have all
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components of a desktop computer
Weigh between six and eight pounds
Can present difficulties in expansion
Designed to conserve space, allow portability,
use less power, and produce less heat
Manufacturers of Cases and Power
Supplies for PCs
Detecting and Correcting Power
Supply Problems
• Measuring voltage of a power supply
• How to upgrade and install power supplies
• Troubleshooting power system and power
supply
Measuring Voltage
of a Power Supply
• Use a multimeter
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Before using, tell it three things
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Whether to measure voltage, current, or resistance
Whether the current is AC or DC
What range of values it should expect
How to measure voltage
 How to measure current
 How to measure continuity
A Digital Multimeter
Measuring Voltage of
a Power Supply
Measuring Voltage Output to an AT
Motherboard
Measuring Voltage Output to an AT
Motherboard
Measuring Voltage Output to an
ATX Motherboard
Measuring Voltage Output to an
ATX Motherboard
Upgrading Your Power Supply
• Sometimes necessary when you add new
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devices
Easiest way to fix a power supply you suspect
is faulty is to replace it
Introduction to Troubleshooting
• Isolate the problem
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Problems that prevent PC from booting
 Problems that occur after a successful boot
• Learn as much as you can by asking questions
of the user
PC Problem Solving
Guidelines for Troubleshooting the
Power System
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Any burnt parts or odors?
Everything connected and turned on? Loose cable
connections? Computer plugged in?
All switches turned on—computer, monitor, surge
protector, UPS, separate circuit breaker? Wall outlet
good?
If fan is not running, turn off computer: Connections
to power supply secure? All cards securely seated?
Troubleshooting the Power System
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Check for correct wire
connections to the
motherboard
Remove all nonessential
expansion cards one at a
time
Vacuum entire unit
Troubleshooting the Power System
• Troubleshooting the power supply itself
• Troubleshooting the power supply fan
• Power problems with the motherboard
• Overheating
Energy Star Systems
(the Green Star)
• Satisfy energy-conserving standards of the
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U.S. EPA
Generally have a standby program that
switches the device to sleep mode when it is
not in use
Apply to computers, monitors, printers,
copiers, and fax machines
Power Management Methods
• Advanced Power Management (APM)
• AT Attachment (ATA) for IDE drives
• Display Power Management Signaling
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(DPMS) standards for monitors and video
cards
Advanced Configuration and Power Interface
(ACPI)
Power Management Features
• Green timer on the motherboard
• Doze time
• Standby time
• Suspend time
• Hard drive standby time
A Power Management Setup Screen
Energy Star Monitors
• Most adhere to DPMS specifications which
allow video card and monitor to go into sleep
mode simultaneously
Windows 98 Energy Star Monitors
Using Energy Star Features
Changing Power Options in
Windows 2000
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Chapter Summary
Basic understanding of electricity
How to measure electricity
Form in which electricity comes to you as house
current
Power supply, backup power sources, how to measure
power supply output, and how to change a defective
power supply
Introduction to form factors
How Energy Star devices save energy