#### Transcript A+ Guide to Managing and Maintaining Your PC, 4e

```Chapter 4
Electricity and Power
Supplies
You Will Learn…
 How electricity is measured
 How to protect your computer system against
damaging changes in electrical power
 About different form factors and computer
cases
 How to detect and correct power supply
problems
Electricity: Basic Introduction
Measures of Electricity
continued…
Measures of Electricity
Voltage
 Electrical force created by the potential
difference in charge
 Measured in units called volts
Voltage
Amps
 Ampere = unit of measurement for electrical
current
Relationship Between Voltage and
Current
 Direct relationship
• As the electrical potential difference (voltage)
•
increases, the electrical current increases
As the voltage decreases, the current decreases
Ohms
 Standard unit of measurement for electrical
resistance
 Resistors are devices used in electrical circuits
to resist the flow of electricity
 As resistance decreases, electricity increases
Relationship Among Voltage, Current,
and Resistance



Voltage and current have a direct relationship
• When voltage increases, current increases
Resistance has an inverse relationship with voltage
and current
• 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
Wattage
 Total amount of power needed to operate an
electrical device
 Measured in watts
 Calculated by multiplying volts by amps in a
system (W = V x A)
AC and DC


AC (alternating current)
• Cycles back and forth rather than traveling in only one
direction
Most economical way to transmit electricity
•
DC (direct current)
• Travels in only one direction
• Type of current required by most electronic devices,
•
including computers
Computer power supplies function as both a transformer
and a rectifier
Computer Power Supply
Hot, Neutral, and Ground
Hot, Neutral, and Ground
 Short circuit
• Occurs when electricity is allowed to flow
uncontrolled from hot line to neutral line or from
hot line to the ground
 Fuse
• Designed to prevent too much current from
flowing through the circuit
Hot, Neutral, and Ground
Hot, Neutral, and Ground
Some Common Electronic Components
Materials Used to Make Electronic
Components
 Conductors
 Insulators
 Semiconductors
 General safety precautions
 Protecting against electricity
 Protecting against electrostatic discharge (ESD
or static electricity) and electromagnetic
interference (EMI)
 Surge protection and battery backup
Protecting Against Electricity
 When working inside a computer
• Turn off the power
• Unplug the computer
• Use a ground bracelet
Static Electricity
 Ground yourself and computer parts, using
static control devices or methods
• Ground bracelet or static strap
• Ground mats
• Static shielding bags
 Caution: Don’t wear a ground bracelet when
working inside a monitor or with high-voltage
equipment such as a laser printer
Using a Ground Bracelet
Using a Ground Bracelet and a Ground
Mat
Using Static Shielding Bags
Electromagnetic Interference
 Caused by the magnetic field produced as a
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 filter AC input
• Surge suppressors (or surge protectors)
• Power conditioners
• Uninterruptible power supply (UPS)
•
Also provides backup power
Uninterruptible Power Supply
 Benefits
• Condition line for brownouts and spikes
• Provide backup power during a blackout
• Protect against very high spikes that could damage
equipment
Uninterruptible Power Supply
What to Consider When
 Cost
 Rating should exceed your total VA or wattage
output by at least 25%
 Degree of line conditioning
 Warranty, service policies, and guarantee
UPS Manufacturers
Computer Case and
Form Factors
 Form factor
• Describes the size, shape, and general makeup of a
•
hardware component
Must match for motherboard, power supply, and
case
Case, Power Supply, and Motherboard
Form Factors
 AT
 ATX (most popular)
 LPX
 NLX
 Backplane systems
 Most common form
factors used on PCs:
• AT
• Baby AT
• ATX
• Mini-ATX
AT Form Factor
ATX Form Factor
NLX Form Factor
Types of Cases
 Desktop cases
 Tower cases
• Minitower
• Midsize (most popular)
• Full-size
 Laptop cases
Desktop Cases
Minitower Cases
Tower and Desktop Cases
Case and Power Supply Vendors
Detecting and Correcting Power Supply
Problems
 Measuring the voltage of a power supply
 Upgrading and installing power supplies
 Troubleshooting the power system and power
supply
Measuring the Voltage of a Power
Supply
 Use a multimeter
• Before using, tell it three things
•
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 Multimeter
How to Measure the Voltage of a Power
Supply
 How to measure the power output for AT and
ATX motherboards
 Procedure for a secondary storage device
Measuring Voltage on an AT
Motherboard
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
 Sometimes necessary when you add new
devices
 Easiest way to fix a power supply you suspect
is faulty is to replace it
Introduction to Troubleshooting
 Categories of problems
• Problems that prevent the PC from booting
• Problems that occur after a successful boot
 Learn as much as you can by asking questions
of the user
Problem-Solving Flow Chart
Troubleshooting the Power System:
Guidelines and Questions




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? Cards securely seated?
Troubleshooting the Power System
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
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
 AT Attachment (ATA) for IDE drives
 Display Power Management Signaling
(DPMS) standards for monitors and video
cards
 Advanced Configuration and Power Interface
(ACPI)
Power Management Features
 Green timer on motherboard
 Doze time
 Standby time
 Suspend time
 Hard drive standby time
Power Management Features
Energy Star Monitors
 Most adhere to DPMS specifications which
allow for the video card and monitor to go into
sleep mode simultaneously
 View and change energy settings in Desktop
Properties window (Windows 2000)
Changing Power Options in Windows
2000
Chapter Summary
 How to measure electricity
 The power supply and backup power sources
 How to measure power supply output
 How to change a defective power supply
 Introduction to form factors
 How Energy Star devices save energy
```