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Chapter 4
Disassembly and Power
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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
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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Detail alternatives for outdated computer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
1-3
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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.
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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!
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Anti-Static Wrist Strap
Disassembly – Figure 4.1
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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.
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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
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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
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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
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Cables and Connectors
• Keyed – A connector or cable that has an extra metal piece that
allows correct connections.
Disassembly – Figure 4.4
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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
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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
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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.
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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.
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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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16
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.
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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
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DC Voltage Reading
• Ensure the polarity (black to ground) is
maintained when taking DC voltage
readings.
19
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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 5-volt 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.
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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.
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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
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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)
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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 8-pin connector
− CFX12V – compact form factor
− TFX12V – thin form factor
− WFX12V – used with high-end workstations and
some servers
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Power Supply Form Factors
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ATX Power Supply
Power – Figure 4.8
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ATX Power Supply Connectors
27
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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
28
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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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29
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.
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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.
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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
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Power Supply ATX Connector
Power – Figure 4.14
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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
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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!
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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.
1-37
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Laptop Power with Travel
Configure for Hibernate rather
than Standby
Turn off wireless
if possible
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
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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
39
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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.
40
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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
41
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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.
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ACPI Operating States
43
Common BIOS Power Settings
44
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.
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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
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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.
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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
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Replacing or Upgrading a Power
Supply
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Sample Computer +12V Usage
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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.
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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
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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)
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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
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Surge Protector Features
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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.
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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.
• Troubleshooting guidelines are listed on pages 131-132.
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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.
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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.
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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
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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.
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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.
1-63
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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.
64
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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.
1-65
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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.
66
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Questions???
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