The Complete A+ Guide
to PC Repair 5/e Update
Chapter 4
Disassembly and Power
Chapter Objectives
After completing this chapter you will:
Describe how static electricity can damage a computer
Describe what type of equipment causes RFI and EMI and what
to do when they occur
List tools a technician needs
Disassemble and reassemble a computer
Define and apply basic electronic terms
Perform basic checks, such as voltage and continuity
Describe the purposes of a power supply
Install a power supply and connect the motherboard and
devices to it
Recognize the different power supply output voltages
Recognize different power connectors
Chapter Objectives (cont.)
After completing this chapter you will:
Apply appropriate power saving techniques
Research and upgrade or replace a power supply
Solve power problems
Define and describe the purpose of different power protection
devices
Describe what to do if an electrical fire occurs
Detail what to do when a computer component fails and must
be thrown away
Detail alternatives for outdated computer
Describe good written communication techniques
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Disassembly Overview
• It is seldom necessary to completely disassemble a computer.
−Sometimes disassembly is accomplished to perform
a preventive maintenance cleaning.
• Disassembly is also helpful in diagnosing
problems of undetermined cause by removing components one
by one or outside the case.
• Disassembly can also help with diagnosing grounding problems.
−Grounding – Occurs when motherboard or adapter isn’t properly
installed and a trace (metal line on the motherboard or adapter) touches
the computer frame and causes the adapter or other components to
stop working.
Electrostatic Discharge (ESD)
• ESD (ElectroStatic Discharge) – Occurs when stored up static electricity is
discharged in an instantaneous surge of voltage. ESD damage is nonrecoverable
and the most susceptible components are the CMOS and RAM chips.
• Anti-static Wrist Strap – A strap connecting the technician to the computer and
that equalizes the voltage potential between the two to prevent ESD. It is
connected to a grounding post or a metal component such as the power supply.
− Electronic symbol for ground:
Warning: A technician should NEVER wear an ESD wrist strap when
working inside a monitor because of high voltages!
Anti-Static Wrist Strap
Disassembly – Figure 4.1
EMI (Electromagnetic Interference)
• EMI (ElectroMagnetic Interference) – Also called
EMR (ElectroMagnetic Radiation) is noise caused by
electrical devices.
−Can travel through electrical wires.
• RFI (Radio Frequency Interference) – Noises that
occur in the radio frequency range.
• Always replace the slot covers for expansion slots
that are not being used.
−This will keep out dust and improve the airflow inside the
computer.
Disassembly
• As with most tasks, the successful disassembly of a
computer begins with preparation.
−Do not remove the motherboard battery
−Use proper grounding
−Take notes
−Have ample workspace
−Do not stack adapters
−Use anti-static bags if possible
−Handle adapter/motherboard by edges
−Handle hard drives carefully
−Do not disassemble a CRT monitor or power supply
Tools
• Having the proper tools to disassemble the computer
can make the task easier and prevent damage to
computer components.
Medium flat-tipped screwdriver
Small flat-tipped “tweaker” screwdriver
Important
Tools to
Have
#1 Phillips screwdriver
#2 Phillips screwdriver
¼-inch nut driver
3/16-inch nut driver
Small diagonal cutters
Needlenose pliers
Reassembly
• Reassembly is easily accomplished if the technician is careful
and diagrams properly during disassembly. Exercise care and
reinstall all components to their original location.
• Three major reassembly components
• Motherboards
• Have plastic connectors on the bottom called standoffs.
• Standoffs – Plastic connectors on the bottom side of a motherboard
that attach it to the case and prevent it from being in contact with
the metal of the computer case.
• Cables
• Connectors
Cables and Connectors
• Keyed – A connector or cable that has an extra metal piece that allows
correct connections.
Disassembly – Figure 4.4
Cables and Connectors
• Pin 1 – Pin 1 on a cable should be connected to Pin 1 on the
connector. The colored stripe on the edge of the cable
identifies Pin 1 on the cable.
−Pin 1 on an adapter will be stenciled beside the connector.
Ribbon Cable’s Pin 1
Disassembly – Figure 4.2
Cables and Connectors
• Solder Joints – Solder connections on the back of
motherboards and adapters. Pin 1 solder joints on the back of
connectors are square.
Pin 1 on a Connector
Disassembly – Figure 4.5
Hard Drives
• Hard drives must be handled carefully
during disassembly because of the delicate nature of
their very intricate construction.
• The read/write heads are located only millimeters from the
platter storing all the data. A small jolt can cause them to
make contact with the platter and cause permanent physical
damage.
• Self-Parking Heads – Read/write heads which pull
away automatically when the computer powers off.
−This feature still would not prevent damaged caused by an
accident or mishandling.
Preventive Maintenance
• Preventive Maintenance – Certain procedures
performed to prolong the life of the computer, such as
cleaning the computer, drive heads, keyboard keys,
printers, and monitor screen.
• MSDS (Material Safety Data Sheets) – Sheets that
contain information about a product, its toxicity,
storage, and disposal.
Tech Tips
• LCD monitor cleaning
• Use wipes specifically made for LCDs
• Soft lint-free cloth dampened with water or a mixture of
isopropyl alcohol and water
• Don’t close laptop lid until screen is dry
• Aerosol can disposal
• Some states have special requirements
• During preventive maintenance calls…
• Check for system, driver, and anti-virus updates
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Basic Electronics Overview
• A technician should know a few basic electronic terms
and concepts when working with computers and testing
components.
• Electricity (or power) - Electrons flowing through a conductor,
just like water flows through a pipe.
• The two types of electricity
• AC (Alternating Current) – Electricity where electrons flow
in both directions and is provided by a wall outlet. Radios,
toasters, and televisions are some devices that use AC
power.
• DC (Direct Current) – Electricity where the electrons flow in
only one direction. Low voltage DC power is used by
computer components, or anything with batteries. The
computer’s power supply converts AC from the wall to DC
for use by internal computer components.
Electronic Terms
• Voltage – A measure of the pressure pushing electrons
through a circuit.
• Measured in volts
• Power supply output is measured in volts (DC) and are typically
+3.3 volts, +5 volts, - 5 volts, +12 volts, and –12 volts.
• The + or – refers to polarity which is simply the condition of being
either positive or negative with respect to some voltage point,
usually 0 volts, or ground.
• Capacitor – A component that holds a charge even after
the computer is turned off.
• CRT monitors have capacitors that can stay charged with high
voltage for hours after being turned off.
• Measured in farads
DC Voltage Reading
• Ensure the polarity (black to ground) is maintained when taking
DC voltage readings.
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Electronic Terms
• Current –The number of electrons going through a circuit every
second.
• Measured in amps (amperes)
• Every device needs some current to operate and a power
supply may be rated at the total amount of current it can
supply at a certain voltage level, such as 20 amps at the 5volt level, or 8 amps at the 12-volt level.
• Power – How much electrical work is being done.
• Measured in watts
• Calculated by multiplying volts times amps.
• Power supplies are described as providing a maximum
number of watts.
Electronic Terms
• Resistance –The amount of opposition to current in an
electronic circuit.
−Measured in ohms
−A good cable or fuse will have very low resistance (close to
zero).
−A broken wire or bad fuse will have very high resistance
(millions of ohms, sometimes displayed as infinite).
• Continuity – A connection from one end of a wire to another.
− Good continuity means little or no resistance.
− Bad continuity means high or infinite resistance, such as
with a broken wire in a cable or a bad fuse.
− Continuity checks can also be used to determine which
connector pins on one end of a cable are attached to what
pins on the other connector end.
Electronic Terms
• The sample meter readings in figure 4.7
demonstrate a good connection - good continuity or
zero resistance, also known as a short, as well as a
broken wire – bad continuity or infinite resistance,
also known as an open.
Power – Figure 4.7
Power Supply Overview
• The power supply is an essential component
because none of the other components can
function without it.
• Converts AC to DC
• Distributes lower voltage to computer components
• Provides cooling with its fan.
• It can be the source of strange and hard to diagnose
problems and easily causes damage to other internal
components.
• Two basic types of power supplies
• Switching (requires a load or something attached to it
using current), which is the type used by a computer
• Linear (provides constant voltage)
Power Supply Form Factors
• Power supplies have form factors (shapes and sizes)
like motherboards do. Form factors today are the ATX,
ATX12V v1.x, and ATX12V v2.x.
• Specific models
−LFX12V – low profile
−SFX12V – small form factor
−EPS12V – used with server motherboards and has an extra 8pin connector
−CFX12V – compact form factor
−TFX12V – thin form factor
−WFX12V – used with high-end workstations and some
servers
Power Supply Form Factors
ATX Power Supply
ATX Power Supply Connectors
ATX Power Supply Connectors
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Power Supply Tech Tips
• Replace a bad power supply with one
of equal or greater wattage.
• A rule of thumb is that if two power supplies are
equal in wattage, the heavier one is better because
it uses a bigger transformer, bigger heat sinks, and
more quality components.
• Not all 24-pin motherboard connectors can accept the
20-pin power supply connector (older ATX power
supply).
• Obtain a 24- to 20-pin adapter
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Power Converters and Y Connectors
• Good to have in the tool kit
Y Connector
Berg-to-Molex Converter
Molex-to-SATA Converter
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Purposes of a Power Supply
• Purposes of the power supply
• Convert AC wall outlet voltage to DC voltage.
• Create and distribute lower DC voltages to
internal components throughout the computer.
• Provide cooling to the computer with its fan.
Warnings
WARNING!
The power supply contains potentially
lethal voltages and current!
• To prevent injury, possible death, or damage to the computer
−ALWAYS exercise extreme caution when working inside the
computer if it is plugged into the wall outlet and/or the power
supply is operating.
−UNPLUG the computer from AC power (power cable from wall
outlet to the power supply) when working with wires (such as
connecting the front panel power switch) or
connecting/disconnecting internal power cables.
−ALWAYS follow ALL the manufacturer’s safety warnings and
instructions for connecting the power supply or working inside
the computer.
Power
Tech Tips
Powering on a power
supply without
anything attached
could damage the
power supply.
An ATX power supply
usually requires only a
motherboard
connection as a
minimum load.
Front Panel Power Connectors
Power –Figure 4.13
Power Supply ATX Connector
Power – Figure 4.14
Power Supply Voltages
• The wires from the power supply carry the following levels of
DC voltage:
• (+) 5 volts: motherboard, most adapters, CD/DVD and hard
drive, some newer drive motors, some chips
• (-) 5 volts: seldom used
• (+) 12 volts: CD/DVD and hard drives (for internal motors)
• (-) 12 volts: seldom used
• (+) 3.3 volts: some chips on motherboards, including CPUs;
also memory, PCI/PCIe adapters, and some laptop fans
• PWR_OK feature
Power Supply Voltages
• Occasionally voltages must be checked on a system.
There are four basic power supply checks that can be
accomplished:
− Wall outlet AC voltage
− DC voltages going to the motherboard
− DC voltages going to a device
− Ground with an outlet tester
• A power supply tester be used to check DC power
levels on the different connectors.
• Exercise extreme caution when checking AC
voltages because voltages harmful to the technician
are present!
Laptop Travel and Storage
• When traveling with a laptop:
• Remove all cards that insert into slots.
• Remove of media disks.
• Ensure that all drive doors and devices are securely
latched.
• Check that the laptop is powered off or in hibernate
mode.
• Carry laptop in a padded case. Never lay laptop
upside down on conveyor belt.
• Never pick a laptop up by the display when the
laptop is opened.
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Laptop Power with Travel
Configure for Hibernate rather
than Standby
Turn off wireless
if possible
De-Fragment the hard drive
before leaving
Keep battery
contacts clean
Avoid
Reduce
using
screen
USB
brightness devices
Avoid using multiple
applications
Seldom save documents—
Turn off autosave
Avoid using
DVD/CD drive.
Avoid temperature
extremes
Laptop Overheating
Locate air vents
Keep them unblocked and clean.
Do not place the computer on your lap to work.
BIOS settings
Check temperature settings for when the fans turn on.
Check manufacturer web site
Check for any fan/temperature monitoring gauges are
available through BIOS or applications
Elevate the laptop
Pads, trays, and mats can be purchased
with fans that are AC or USB-powered
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Laptop Power
• Laptops either use a battery (DC
power) or an AC connection.
• On most models, the battery recharges when the
laptop has AC power attached.
• Some power supplies and laptops have input voltage
selectors.
• Others have the ability to accept input from 100 to
240 volts for use in various countries.
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Laptop Tips
• Most laptops use Li-ion batteries.
• These batteries last longer if they are kept cool.
• 40% charged and place in refrigerator
• Don’t power on after a temperature change
• Allow to return to room temperature
• Avoid direct sunlight
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ACPI (Advanced Configuration and Power Interface)
• Allows the operating system, BIOS, and motherboard to have
control over various devices’ power and modes of operation
−CPU
−Monitor
−CD/DVD drive
−Network adapter
−Printer
• Two common BIOS and adapter features that take advantage of
ACPI
−Wake on LAN allows a network administrator to control power
to a workstation and come out of sleep mode for operating
system, application, and anti-virus updates.
−Wake on Ring allows a computer to come out of sleep mode to
receive phone calls, faxes, and e-mails.
ACPI Operating States
44
Common BIOS Power Settings
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ACPI and Coming Out of Sleep Mode
• Sometimes a computer will not come out of sleep
mode and the power or reset button has to be
pressed.
• A screen saver conflicts with ACPI
• Not all adapters or devices are ACPI-compliant
• An adapter or device has an outdated driver
• Keep the screen saver timeout value shorter than the
power saver timeout value with energy efficient
monitors.
ACPI and Not Going into Sleep Mode
• Sometimes a computer will not go into sleep mode.
• Determine if ACPI is enabled in the BIOS
• Try disabling the antivirus application
• Disable the screen saver to see if it is the problem
• Determine if all drivers are ACP-compliant
• Determine if power management is enabled
through the operating system
• Disconnect USB devices
Replacing or Upgrading a Power Supply
• Its important to make sure that the power supply
has enough power to run all the devices in the
computer.
• If you’re adding or upgrading devices, make sure
you won’t be exceeding the wattage rating for the
power supply with the new configuration.
• If you upgrade or replace the power supply, make
sure its power rating is high enough to meet the
needs of the computer configuration and the power
supply is the right size and form factor to fit the
computer case.
Replacing or Upgrading a Power Supply
• Dual rail power supply – has two +12V output lines,
one used for the CPU.
• Triple rail power supply – has three +12V output lines
for devices.
• Multi-core processors and video cards use 12V power
in addition to devices that have motors such as hard
drives and CD/DVD drives.
• Ensure enough amperage is provided for all installed
devices that use 12V power.
• An auto-switching power supply monitors incoming
voltage and automatically switches itself accordingly.
• Commonly found in laptops (110 vs. 220)
Replacing or Upgrading a Power Supply
Sample Computer +12V Usage
Power Supply Problems
• You should never take the power supply apart unless you have a background in
electronics. Replace the entire power supply when it is faulty; power supplies are
inexpensive.
• Power supply problems are usually easy to check. You should:
• Check to see that the power supply is plugged into the wall outlet and snugly
into the power supply. Replace it to verify functionality.
• If the power supply has never worked before, check the 115/230 switch to be
sure its in the 115 position.
• Ensure the power supply fan is turning. If not, check the wall outlet for proper
AC voltages with an AC circuit tester.
• If a surge strip is used, make sure its powered on, then try another outlet in
the strip, or another strip to verify functionality.
Symptoms of Power Supply Problems
• The computer’s power light is •
off.
• The power supply fan does not
turn with computer powered •
on.
•
• The computer sounds a
continuous beep.
•
• When the computer powers
on, it does not beep at all.
•
• When the computer powers
on, it sounds repeating short
beeps.
During POST, a 02X or parity
POST error code appears
(where X is any number).
The computer reboots without
warning.
The power supply fan is noisy.
The power supply is too hot to
touch.
The monitor power light is on,
but nothing appears. No PC
power light is on.
Adverse Power Conditions
• Do not create a trip hazard with a surge strip
Adverse Power Protection
• Although power supplies have built-in protection
against adverse power conditions, the best
protection for a computer during a power outage or
thunderstorm is to unplug it.
• Three devices are commonly used to protect the
power supply from adverse conditions. They are:
• A surge protector
• A line conditioner
• An Uninterruptible Power Supply (UPS)
Surge Protectors
• Surge protector – Is commonly a six-outlet strip with
built-in protection against overvoltage.
• MOV (Metal Oxide Varistor) – An electronic
component in most surge protectors that protects
the computer or device that plugs into one of the
outlets on the surge strip.
Power –Figure 4.17
Surge Protector Features
Line Conditioners
•
Line Conditioners – protect the computer from
overvoltages, undervoltages, and adverse noise conditions
over electrical lines.
• The line conditioner monitors AC electricity and adjusts the
voltage
being sent to the computer.
Uninterruptable Power Supply (UPS)
• UPS (Uninterruptable Power Supply) – Provides power to a
computer or device for a limited amount of time when there is a
power outage. If the power from the wall outlet goes out, the
battery continues to provide power for at least long enough to
shut down the computer properly.
• Sine Wave – Pattern for AC voltage in its correct form and what
you want the UPS you choose to have for its output.
• Square Wave – The AC voltage pattern described by cheaper,
and thus less effective, UPS.
Uninterruptable Power Supply (UPS)
• Three things to look for when purchasing
a UPS are to be sure that:
• There is sufficient battery time to
protect all devices.
• The amount of current the UPS
produces is sufficient to protect all
devices.
• The output waveform is a sine wave.
Standby Power Supply (SPS)
• SPS (Standby Power Supply) – Provides power to a
computer only when it loses AC power.
• Does not provide protection against noise or over/under
voltages.
• The SPS must detect a power-out condition first and then
switch over to the battery. Because of this, switching time
is very important. Any time under five milliseconds is
acceptable.
Phone Line Isolator
• Phone line isolator – Also called a modem isolator, provides
protection against phone line surges.
• Goes in between a modem and the wall jack to protect
the computer against power surges on the phone line.
• Sometimes contained in a surge strip
Electrical Fires
• Electrical fires in computers are uncommon, but can still
occur. If possible, unplug the computer if there is an
electrical fire, but don’t risk injury to do so.
• Type C Fire Extinguisher – A type of extinguisher used
only on electrical fires.
• Type A-B-C Fire Extinguisher – A type of extinguisher
used on either Type A (wood, paper, cloth), Type B
(flammable liquids or gases), or Type C fires.
Computer Disposal/Recycling
• Computers and electronic devices can contain
materials which pose a threat to the environment
such as: lead, cadmium, mercury, nickel, and zinc.
• Every state has regulations for disposing of
electronic equipment.
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Alternatives to Displosal
• Donate to schools and charities
• If the operating system is not put on another system, leave on
the donated computer and provide proof of purchase.
• Erase data stored on the donated computer
• Recycle outdated electronics
• Many companies accept old parts and can reuse them
• Buy electronics designed with saving resources in mind
and that are energy efficient.
• Check with the computer/component manufacturer to
see if they have a recycling program.
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Written Communication Skills
• Technicians use written skills when documenting
problems and writing emails.
• Documentation can include a basic description of
what was done, and time spent on the job.
• It should be written in a manner as to be helpful to other
technicians.
• Suggested guidelines for effective emails include using
a spelling and grammar checker, and using proper
capitalization, never only uppercase or lowercase
letters.
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Effective Email
• Don’t use email when a meeting or phone call is more
appropriate
• Include a subject in the email subject line
• Do not write an email when angry
• Send email only to the appropriate people
• Stick to the point of the email; do not be wordy
• Use a spell/grammar checker
• Use proper grammar, capitalization, punctuation, and spelling.
• Do use all uppercase or lowercase letters.
• Write each email as if it were being posted to a billboard.
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