View
5
Download
0
Category
Preview:
Citation preview
Chapter 8Power Supplies
MELJUN CORTESMELJUN CORTES
© 2007 The McGraw-Hill Companies, Inc. All rights reserved
OverviewIn this chapter, you will learn to
Explain the basics of electricityDescribe the details about powering the PCInstall, maintain, and troubleshoot power
supplies
Understanding Electricity
© 2007 The McGraw-Hill Companies, Inc. All rights reserved
Measuring ElectricityVoltage—pressure of electrons in a wire
Unit of measurement: Volts (V)Current— flow (or amount) of electrons in a wire
Unit of measurement: Ampere (A)When voltage is applied to a wire, electrons flow,
producing current
Wattage—measure of power consumed or needed Unit of measurement: Watt (W) W = V * A
Resistance—impedance or opposition to the flowUnit of measurement: Ohm (Ω)
© 2007 The McGraw-Hill Companies, Inc. All rights reserved
Measuring ElectricityWire has amperage rating
Defines how much amperage it can handle i.e., 20 amp, 30 amp
If you exceed amperage Wires heat up—may break
Circuit breakers are heat sensitiveSense when amperage exceeds thresholdBreaks the circuit to stop the flow of
electricity
© 2007 The McGraw-Hill Companies, Inc. All rights reserved
Two Types of CurrentAlternating Current (AC)—electrical
current flows in both directionsElectricity provided at wall socketFrequency of alternations measured in
cycles per second, or hertz (Hz)
Direct Current (DC)—electrical current flows in one directionElectricity provided by batteries
Powering the PCCompTIA A+Essentials
Essentials
© 2007 The McGraw-Hill Companies, Inc. All rights reserved
Types of PowerPCs use DC voltage
Power companies supply AC voltage
The power supply in a computer converts high-voltage AC to low-voltage DC
© 2007 The McGraw-Hill Companies, Inc. All rights reserved
Supplying ACIn the U.S., 115 VAC is standardOther 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
© 2007 The McGraw-Hill Companies, Inc. All rights reserved
Outlet VoltagesHot and neutral provide
path for ACHot has 115 V
Neutral carries no voltage
Ground used for safetyReturns excess electricity
to ground Wall outlet
© 2007 The McGraw-Hill Companies, Inc. All rights reserved
Multimeter BasicsA multimeter (or Volt-
Ohm meter: VOM) measures:VoltageResistanceContinuity
WarningSet it properly before
measuringIf not, damage can occur
© 2007 The McGraw-Hill Companies, Inc. All rights reserved
Testing AC VoltageVerifies wiring of outlet
Hot should be 115 VAC
Neutral completes the circuit
Ground should go to ground
© 2007 The McGraw-Hill Companies, Inc. All rights reserved
Surge Suppressors Surge suppressors provide protection against power
surges Insert between the power supply and the outlet Joule is a unit of electrical energy
Surge suppressor rated by joulesHigher joules = better protection
Some protect more than AC surgesPhone lines for traditional modemsCable connections for cable modems
© 2007 The McGraw-Hill Companies, Inc. All rights reserved
Uninterruptible Power Supply
An uninterruptible power supply (UPS) provides protection against 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
© 2007 The McGraw-Hill Companies, Inc. All rights reserved
Supplying DCThe power supply acts as a step-down
transformer 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
© 2007 The McGraw-Hill Companies, Inc. All rights reserved
Power ConnectorsMotherboard
20- or 24-pin P14-, 6-, 8-pin
PeripheralsMolex
Mini
SATA
© 2007 The McGraw-Hill Companies, Inc. All rights reserved
Power ConnectorsConnectors are keyed
Can plug in only one way
Splitters and adapters
Can create two power connectors from one
Can convert Molex to SATA
© 2007 The McGraw-Hill Companies, Inc. All rights reserved
Soft PowerATX power supplies first to use
P1 power connector
Always on when plugged in5 V supplied to motherboard when plugged
in
Configured in CMOS
© 2007 The McGraw-Hill Companies, Inc. All rights reserved
Power Supply VersionsATX 12 V 1.3
First widespread update to ATX PS
EPS 12 VIntroduced for server motherboards
ATX 12 V 2.0Overcame problem overloading 12 V railProvides multiple 12 V rails
© 2007 The McGraw-Hill Companies, Inc. All rights reserved
P4 ConnectorMany motherboards require a
second, four-wire connector Provides more 12 V power Can be MolexCan be PCI-E
© 2007 The McGraw-Hill Companies, Inc. All rights reserved
IT TechnicianCompTIA A+Technician
Niche MarketPower Supply Form Factors
© 2007 The McGraw-Hill Companies, Inc. All rights reserved
Form FactorsNiche market power supply form factors
TFX12V, SFX12V, CFX12V, LFX12V
Active PFCPower Factor CorrectionCommon in quality power suppliesEliminates harmonics
© 2007 The McGraw-Hill Companies, Inc. All rights reserved
Wattage RequirementsEvery device requires some wattage
Often starting requirements are higher than running requirements
Power supplies don’t run at 100% efficiencyATX 12 V requires power supplies to be at
least 70% efficient
General recommendationUse at least a 400 W power supplyEnough extra for starting and future growth
© 2007 The McGraw-Hill Companies, Inc. All rights reserved
Installing, Maintaining, and Troubleshooting Power Supplies
© 2007 The McGraw-Hill Companies, Inc. All rights reserved
InstallingRemoving
Disconnect wiresRemove 4 standard screwsRemove PS
To install Place PS in caseReplace screwsConnect wires
© 2007 The McGraw-Hill Companies, Inc. All rights reserved
ATX Soft Power and CMOS
An ATX power supply never turns offContinues to supply 5V to the
motherboard as long as it is connected to the power outlet
Always unplug an ATX power supply before working on it
Some ATX power supplies provide a real on/off switch on the back
Can use a screwdriver or car keys to short the two power jumpers to turn the system on or off in special circumstances
© 2007 The McGraw-Hill Companies, Inc. All rights reserved
Cooling The power supply fan provides basic cooling
for the PC
Fan keeps the voltage regulators cool and provides a constant flow of cool air through the computer
If power supply fan stops, replace power supply
Many fans have sensors to detect when they should run quicker
© 2007 The McGraw-Hill Companies, Inc. All rights reserved
Cooling Case fan provides extra cooling for PC
Most modern computers have case fans
Often plug into Molex connector
Connector adapters can be used
© 2007 The McGraw-Hill Companies, Inc. All rights reserved
Maintaining Airflow Keep case closed
Keep covers on case
If an expansion card is removed from the PC, be sure to cover the hole with a slot cover
Without proper airflow, the CPU can overheat and destroy itself
© 2007 The McGraw-Hill Companies, Inc. All rights reserved
Reducing Fan NoiseSome fans can be adjusted
Manually adjustable with knobSoftware adjustable by sensing heat
Larger fans that spin slower are quieter
Higher-end fans are quieterUse better bearings
© 2007 The McGraw-Hill Companies, Inc. All rights reserved
CMOS Fan OptionsCan monitor PC’s health by showing
temperaturesDoesn’t control fansCan set fan thresholds for alarms
© 2007 The McGraw-Hill Companies, Inc. All rights reserved
Freeware ToolSpeedfan
Allows monitoring of fan speeds
Can set fan speeds
Hundreds of chipsetssupported
© 2007 The McGraw-Hill Companies, Inc. All rights reserved
When Power Supplies DiePower supplies fail in two ways:
Sudden deathWhen the fan doesn’t turn and no voltage is presentComputer simply stops working
Slowly over time Intermittent errorsOutput voltages may exceed specs (± 10%)
© 2007 The McGraw-Hill Companies, Inc. All rights reserved
Power Supply TestPut the black lead onto
any black wire connection
Put the red lead onto colored wire
• 12 V ± 10%– 10.8 to 13.2 V– If readings are outside
tolerance and symptoms exist, replace power supply
• 5V ± 10%– 4.5 to 5.5 V
• 3.3 V ± 10%– 2.97 to 3.63 V
© 2007 The McGraw-Hill Companies, Inc. All rights reserved
Power Supply TestPower supplies need a load
Plug into motherboardPlug into tester
Check power switchesIf faulty, can turn on
with motherboard jumper
© 2007 The McGraw-Hill Companies, Inc. All rights reserved
When Power Supplies Die Slowly
Intermittent problemsSometimes occur, sometimes don’tYou could measure voltage now and it’s good;
10 minutes later, system crashes
A dying power supply can causeRandom lockups and rebootsSporadic boot-up difficulties
When you encounter intermittent symptoms, consider replacing the power supply
© 2007 The McGraw-Hill Companies, Inc. All rights reserved
Fuses and FireCircuit breakers are heat-sensitive
Sense when amperage exceeds thresholdBreaks the circuit to stop flow of electricity
Fuses blow for a reasonPower supply is malfunctioningAs a designed safety precaution, fuses
blow (break) to stop circuit
Alternative is a possible fire
© 2007 The McGraw-Hill Companies, Inc. All rights reserved
Fire ExtinguishersClass A
Ordinary combustibles such as paper and wood
Class BFlammable liquids such as gasoline
Class CLive electrical equipment
Use only Class C extinguishers on electrical fires
© 2007 The McGraw-Hill Companies, Inc. All rights reserved
Beyond A+ It glows
Fancy colors, light up, and have extra fans
Module power suppliesReduced cables
Rail powerLook for power supplies that
offer 16 to 18 A per 12 V rail
© 2007 The McGraw-Hill Companies, Inc. All rights reserved
Recommended