PC Maintenance: PC Maintenance: Preparing for A+ Preparing for A+

CertificationCertificationChapter 3: Case, Electricity, and Chapter 3: Case, Electricity, and

Power SuppliesPower Supplies

Chapter 3 ObjectivesChapter 3 Objectives

Select an appropriate case for a PCSelect an appropriate case for a PC Understand electrical basicsUnderstand electrical basics Select an appropriate power supplySelect an appropriate power supply Troubleshoot a PC using electrical testingTroubleshoot a PC using electrical testing Select appropriate power conditioning and Select appropriate power conditioning and

backup devicesbackup devices

Selecting a CaseSelecting a Case

ConstructionConstruction Form Factor (AT, ATX)Form Factor (AT, ATX) Number of drive baysNumber of drive bays Power supply (if included)Power supply (if included)

Case Form FactorsCase Form Factors

ATX:ATX: Loose wires Loose wires

coming from coming from power switch, power switch, will connect to will connect to motherboard motherboard laterlater

Bezel for the Bezel for the motherboard’s motherboard’s built-in I/O ports built-in I/O ports in backin back

Case Form FactorsCase Form Factors

AT:AT: Power switch Power switch

connects to connects to power supplypower supply

Slots in case Slots in case floor for plastic floor for plastic stand-offsstand-offs

Drive BaysDrive Bays

InternalInternal ExternalExternal

SmallSmall Hard diskHard disk 3 ½” floppy3 ½” floppy

ZIP driveZIP drive

LargeLarge Some older hard Some older hard disksdisks

CDCD

5 ¼” floppy5 ¼” floppy

Drive BaysDrive Bays

Electricity BasicsElectricity Basics

VoltageVoltage CurrentCurrent WattageWattage ResistanceResistance

VoltageVoltage

Difference in charge between the positive Difference in charge between the positive and negative polesand negative poles

Can be positive or negative volts (v)Can be positive or negative volts (v) Ordinary household current is 110v in the Ordinary household current is 110v in the

USA, or 220v in most of EuropeUSA, or 220v in most of Europe

CurrentCurrent

Measurement of the volume of electricityMeasurement of the volume of electricity Measured in amperes, or ampsMeasured in amperes, or amps Controlled by the device that is drawing Controlled by the device that is drawing

the currentthe current

WattageWattage

Derived by multiplying voltage and currentDerived by multiplying voltage and current Examples: Examples:

5 amps of +12v power = 60 watts5 amps of +12v power = 60 watts 1.5 amps of +5v power = 7.5 watts1.5 amps of +5v power = 7.5 watts 10 amps of +3.3v power = 33 watts10 amps of +3.3v power = 33 watts

ResistanceResistance

Amount of obstacle in the electricity’s pathAmount of obstacle in the electricity’s path Measured in ohms (Measured in ohms (Ω)Ω) Resistance of less than 20 ohms required Resistance of less than 20 ohms required

for electrical operationfor electrical operation Infinite ohms ( ∞ ), no connectionInfinite ohms ( ∞ ), no connection

GroundingGrounding

Creating a path of little resistance to the Creating a path of little resistance to the groundground

Acts as a protection against over-voltageActs as a protection against over-voltage Achieved by the third prong in an outlet Achieved by the third prong in an outlet

plugplug

AC and DCAC and DC

AC: Alternating CurrentAC: Alternating Current Ordinary household currentOrdinary household current Alternates positive and negative poles at 60 Hz Alternates positive and negative poles at 60 Hz Good for sending power over long distancesGood for sending power over long distances

DC: Direct currentDC: Direct current BatteriesBatteries Positive and negative poles stay fixedPositive and negative poles stay fixed Lower overheadLower overhead PortablePortable

Electrical MeasurementsElectrical Measurements

Analog multimeterAnalog multimeter Uses a needle Uses a needle

gaugegauge Continuously Continuously

variablevariable Digital multimeterDigital multimeter

Uses a digital Uses a digital displaydisplay

Precise valuesPrecise values More suitable for More suitable for

computerscomputers

Measuring ResistanceMeasuring Resistance

Set multimeter to ohmsSet multimeter to ohms Place probes on either end of the wire or Place probes on either end of the wire or

circuit in questioncircuit in question

Measuring VoltageMeasuring Voltage

Must be Must be measured with measured with computer oncomputer on

Use back-Use back-probingprobing

Place black Place black probe on probe on grounding wire grounding wire (black)(black)

Place red probe Place red probe on wire to be on wire to be testedtested

Measuring CurrentMeasuring Current

Must be measured with computer onMust be measured with computer on Multimeter must be placed in-lineMultimeter must be placed in-line Difficult to do with most computer Difficult to do with most computer

componentscomponents

Types of Power SuppliesTypes of Power Supplies

Form factorForm factor ATAT ATXATX Other sizes Other sizes

WattageWattage

AT Power SupplyAT Power Supply

P8 and P9 connectors to motherboardP8 and P9 connectors to motherboard Power switch attached directlyPower switch attached directly +5v, -5v, +12v, and -12v power+5v, -5v, +12v, and -12v power

AT ConnectorsAT Connectors

ATX Power SupplyATX Power Supply

Single 20-wire connector to motherboardSingle 20-wire connector to motherboard No direct connection to power switchNo direct connection to power switch +5v, -5v, +12v, -12v, and +3.3v power+5v, -5v, +12v, -12v, and +3.3v power

ATX Power Supply WiresATX Power Supply Wires

Power Supply ConnectorsPower Supply Connectors

MolexMolex Used for most drive typesUsed for most drive types

MiniMini Used for 3.5” floppy drivesUsed for 3.5” floppy drives

Determining Wattage Determining Wattage RequirementsRequirements

Read label on power supplyRead label on power supply Calculate wattage drawn by each Calculate wattage drawn by each

componentcomponent Compare total amount drawn to labelCompare total amount drawn to label

Failed Power SupplyFailed Power Supply

Fan won’t spinFan won’t spin Inconsistent power provided (fan revs and Inconsistent power provided (fan revs and

sags)sags) System will not boot (appears dead)System will not boot (appears dead)

Overloaded Power SupplyOverloaded Power Supply

Typically overloads at startupTypically overloads at startup Problems occur when drives spin upProblems occur when drives spin up System may spontaneously reboot when System may spontaneously reboot when

multiple drives are accessedmultiple drives are accessed

Testing a Power SupplyTesting a Power Supply

Check voltage on the Power_Good pinCheck voltage on the Power_Good pin AT: Pin 1 on P8 (orange wire)AT: Pin 1 on P8 (orange wire) ATX: Pin 8 (gray wire)ATX: Pin 8 (gray wire)

Use back-probingUse back-probing Range should be +3v to +6vRange should be +3v to +6v

Surge suppressorSurge suppressor

No backup powerNo backup power Protects from damage due to spikesProtects from damage due to spikes Does not protect from damage due to sagsDoes not protect from damage due to sags

Uninterruptible Power SupplyUninterruptible Power Supply

Standby UPSStandby UPS Serves as surge Serves as surge

suppressorsuppressor Switches to battery Switches to battery

backup when neededbackup when needed Online UPSOnline UPS

Serves as a surge Serves as a surge suppressorsuppressor

Runs constantly on Runs constantly on battery, recharged battery, recharged from ACfrom AC