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Chapter 8
Power Supplies
MELJUN CORTES
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2007 The McGraw-Hill Companies, Inc. All rights reserved
Overview
In this chapter, you will learn to
Explain the basics of electricity
Describe the details about powering the PC
Install, maintain, and troubleshoot power supplies
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2007 The McGraw-Hill Companies, Inc. All rights reserved
Measuring Electricity
Voltagepressure of electrons in a wire Unit of measurement: Volts (V)
Currentflow (or amount) of electrons in a wire
Unit of measurement: Ampere (A)
When voltage is applied to a wire, electrons flow,producing current
Wattagemeasure of power consumed or needed
Unit of measurement: Watt (W) W = V * A
Resistanceimpedance or opposition to the flow
Unit of measurement: Ohm ()
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Measuring Electricity
Wire has amperage rating
Defines how much amperage it can handle i.e., 20 amp, 30 amp
If you exceed amperage Wires heat upmay break
Circuit breakersare heat sensitive
Sense when amperage exceeds threshold Breaks the circuit to stop the flow of electricity
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Two Types of CurrentAlternating Current(AC)electrical current
flows in both directions
Electricity provided at wall socket
Frequency of alternations measured in
cycles per second, or hertz (Hz)
Direct Current(DC)electrical current
flows in one direction
Electricity provided by batteries
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Powering the PC
CompTIA A+
Essentials
Essentials
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Types of Power
PCs use DC voltage
Power companies supply AC voltage
The power supply in a computer converts high-
voltage AC to low-voltage DC
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Supplying AC
In the U.S., 115 VAC is standard
Other countries use 230 VAC
Many PCs may have a small switch on the back to
choose 115 or 230 V (used in other countries)
Pay attention to this switch, especially when
traveling overseas
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Outlet Voltages
Hot and neutral provide pathfor AC
Hot has 115 V
Neutral carries no voltage
Ground used for safety
Returns excess electricity to
groundWall outlet
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Multimeter Basics
A multimeter (or Volt-Ohmmeter: VOM) measures:
Voltage
Resistance
Continuity
Warning
Set it properly before
measuring
If not, damage can occur
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Testing AC Voltage
Verifies wiring of outlet
Hot should be 115 VAC
Neutral completes the circuit
Ground should go to ground
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Surge Suppressors
Surge suppressorsprovide protection against power surges Insert between the power supply and the outlet
Jouleis a unit of electrical energy
Surge suppressor rated by joules
Higher joules = better protection
Some protect more than AC surges
Phone lines for traditional modems
Cable connections for cable modems
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Uninterruptible Power Supply
An uninterruptible power supply(UPS) provides protectionagainst a power dip or power outage
Contains a battery that provides continuous AC power
Provides surge protection and power conditioning
Constantly charges battery
All UPSs measured in watts and volts-amps
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Supplying DC
The power supplyacts as a step-downtransformer
Converting AC into 5, 12, and 3.3 V DC
PCs use a 12 V current to power motors on devices
such as hard drives and CD-ROM drives
PCs use a 5-volt/3.3-volt current to support onboard
electronics
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Power Connectors
Motherboard 20- or 24-pin P1
4-, 6-, 8-pin
Peripherals
Molex
Mini
SATA
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Power Connectors
Connectors are keyed
Can plug in only one way
Splitters and adapters
Can create two power
connectors from one
Can convert
Molex to SATA
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Soft Power
ATX power supplies first to use P1 power connector
Always on when plugged in
5 V supplied to motherboard when plugged in
Configured in
CMOS
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Power Supply Versions
ATX 12 V 1.3 First widespread update to ATX PS
EPS 12 V
Introduced for server motherboards
ATX 12 V 2.0
Overcame problem overloading 12 V rail
Provides multiple 12 V rails
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P4 Connector
Many motherboards require a second,four-wire connector
Provides more 12 V power
Can be Molex
Can be PCI-E
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IT Technician
CompTIA A+
Technician
Niche MarketPower Supply Form Factors
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Wattage Requirements
Every device requires some wattage Often starting requirements are higher than running
requirements
Power supplies dont run at 100% efficiency
ATX 12 V requires power supplies to be at least
70% efficient
General recommendation
Use at least a 400 W power supply
Enough extra for starting and future growth
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Installing, Maintaining, and
Troubleshooting Power Supplies
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Installing
Removing Disconnect wires
Remove 4 standard screws
Remove PS
To install
Place PS in case
Replace screws Connect wires
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ATX Soft Power and CMOS
An ATX power supply never turnsoff
Continues to supply 5V to themotherboard as long as it isconnected to the power outlet
Always unplug an ATX powersupply before working on it
Some ATX power supplies provide a
real on/off switch on the back
Can use a screwdriver or car keysto short the two power jumpers toturn the system on or off inspecial circumstances
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Cooling
Case fanprovides extra cooling for PC
Most modern computers have case fans
Often plug into Molex connector
Connector adapters can be used
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Maintaining Airflow
Keep case closed
Keep covers on case
If an expansion card is removed from the PC, besure to cover the hole with a slot cover
Without proper airflow, the
CPU can overheat anddestroy itself
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Reducing Fan Noise
Some fans can be adjusted Manually adjustable with knob
Software adjustable by sensing heat
Larger fans that spin slower are quieter
Higher-end fans are quieter
Use better bearings
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CMOS Fan Options
Can monitor PCs health by showingtemperatures
Doesnt control fans
Can set fan thresholds for alarms
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Freeware Tool
SpeedfanAllows monitoring of fan speeds
Can set fan speeds
Hundreds of chipsets
supported
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When Power Supplies Die
Power supplies fail in two ways:
Sudden death When the fan doesnt turn and no voltage is present
Computer simply stops working
Slowly over time Intermittent errors
Output voltages may exceed specs ( 10%)
P S l T
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Power Supply Test
Put the black lead onto anyblack wire connection
Put the red lead onto colored
wire
12 V 10%
10.8 to 13.2 V
If readings are outsidetolerance and symptomsexist, replace powersupply
5V 10% 4.5 to 5.5 V
3.3 V 10%
2.97 to 3.63 V
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Power Supply Test
Power supplies need a load Plug into motherboard
Plug into tester
Check power switches
If faulty, can turn on
with motherboard jumper
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Fuses and Fire
Circuit breakersare heat-sensitive Sense when amperage exceeds threshold
Breaks the circuit to stop flow of electricity
Fusesblow for a reason
Power supply is malfunctioning
As a designed safety precaution, fuses blow
(break) to stop circuit
Alternative is a possible fire
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Fire Extinguishers
Class A Ordinary combustibles such as paper and wood
Class B
Flammable liquids such as gasoline
Class C
Live electrical equipment
Use only Class C extinguishers on electrical fires
B d A
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Beyond A+
It glows
Fancy colors, light up, and have extra
fans
Module power supplies
Reduced cables
Rail power
Look for power supplies that offer 16
to 18 A per 12 V rail
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