Troubleshooting I
CAPL1102
Unit 1 (Theory)
General Safety Principles
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define terms associated with electrical safety
list two or more hazards of working with
electrical and electronic equipment
state two or more distinct health risks
associated with working with computers
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identify good working environments for
computer systems
handle electronic components of the
computer in a safe manner
General Safety Principles
General Safety Principles
A basic understanding of the properties of electricity is
necessary to be able to understand how a computer
operates.
Electricity flows through a circuit in much the same manner as
water flows through a pipe or hose.
When water is flowing through a pipe, it is pushed along by a
measurable rate of pressure. Electricity also flows through
a circuit with a measurable pressure. This pressure is
measured in units called volts.
General Safety Principles
While the water is flowing through a pipe or hose, it
experiences some loss of pressure through friction. The
same thing happens to electricity as it flows through a
circuit: there is friction that causes a loss in pressure.
This friction is called resistance and is measured in units called
ohms.
General Safety Principles
The amount of water that flows through a pipe for a specified
length of time, such as the gallons-per-minute, is called the
volume of the water flow.
For an electrical current, volume, or the rate of flow, is
measured in amps.
General Safety Principles
Another electrical term you should know is watt.
The amps (rate of electrical flow) in combination with the volts
(pressure in a circuit) form the watts, or the electrical
power in a circuit. When an electrical circuit is open, there
is no current or flow in the electricity.
However, there can still be pressure (volts) in the circuit.
General Safety Principles
In summary,
General Safety Principles
In summary,
General Safety Principles
A standard household electrical outlet has voltage (electrical
pressure) just waiting for you to plug in a household
appliance, which completes the circuit and starts the flow.
This is why you don’t want to stick your finger into an
electrical outlet. You would be supplying the extra circuitry
to close the circuit and cause the electricity to flow—
through you, in this case. And because you are not well
insulated and you don’t make a particularly good conductor
of electricity, you feel the electricity flowing through you
as a shock. The degree of shock you feel when you close the
circuit depends on the watts, or electrical power in the
circuit.
General Safety Principles
All computer professionals should know Ohm’s Law
From this formula, or a derivation of this formula, all basic
power calculations can be performed.
Ohm’s law states that the current flowing through a conductor,
or resistance, is linearly proportional to the applied
potential difference (volts)
General Safety Principles
For example,
The voltage (potential energy of the circuit) equals the
amperage (the current or flow of electricity) times any
resistance to that flow of electricity. From this, it can be
seen that for a given voltage, the more resistance in a
circuit, the lower the current flow.
General Safety Principles
An electrical current is a movement of electrons through a
copper wire or some other conducive property.
There are two types of electrical currents/power:
 alternating current (AC)
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•

110 volts to 120 volts American Standard
220 volts European Standard
direct current (DC)
General Safety Principles
Alternating Current (AC) changes the direction of the
electrical flow at a rate of about 60 times per second. The
voltage changes from a positive charge to a negative
charge, causing the electrical flow to change directions.
The term AC power means that the flow of electrons in the
wires moves back and forth or alternates (there are no
positive or negative poles).
General Safety Principles
AC is the type of power that we get from the electrical outlets
in our houses.
The reason that we use AC power in our businesses and homes
is that it is a very efficient way to transport power over
long distances.
AC power is measured in terms of voltage and frequency; where
voltage represents the potential power and the frequency
represents how many times per second the voltage
alternates.
Typical power is delivered to our homes as 110 to 120 Volts at
60 Hz (Hertz – cycles per second).
General Safety Principles
The electrical flow in a direct current (DC) keeps a constant
pace and flows in the same direction all the time. Direct
current flows from a negative charge to a positive charge
and does not fluctuate.
For example,
A battery has distinct poles, one positive and one negative,
where its current flows from the negative pole to the
positive pole.
The advantage of using DC power is that it is easy to control.
DC is the power of choice for electronic equipment.
General Safety Principles
In summary,
Computers use low voltage DC power to operate their
components.
AC power is what we are likely to have at our standard
household electrical outlets, but DC is what the computer
must have to operate properly.
General Safety Principles
What’s wrong with this picture?
The computer needs DC power, but our wall outlet provides AC
power.
General Safety Principles
Electrical Outlet
AC power is supplied to a computer via the electrical outlets or
receptacles, and then converted into DC power to run the
components inside the computer.
When connecting a computer or any other electronic equipment,
you must be sure to use a properly grounded outlet.
General Safety Principles
Electrical Outlet cont’d
Most modern construction today will require all outlets
facilitate three-prong.
While we can still purchase an adapter to convert the three-prong plug
that comes with a computer to a two-prong plug for older receptacles, it is
not advised as it is dangerous.
The reason for the third connection (the small round one) is to
provide a safety ground.
This protects both the user and the computer from short
circuits, as the grounded receptacle provides a direct
connection to ground, giving the electricity an alternate
path should things get out of control.
General Safety Principles
Inside our PC is a module called the power supply, which
converts the electricity in your household circuit (HC) from
AC power into the DC power that the computer needs.
Thus, all of the circuitry, the electronics on the motherboard,
including the microprocessor, the disk drive motors, and all
other electrical parts, require DC power to operate.
It is the function of the power supply to convert the AC power
to DC power.
General Safety Principles
Thus, the energy or power to drive a computer is derived from
electricity; which can be sourced from AC or a battery.
A computer requires a reliable source of power.
As computer technicians, we do not have to be electricians or
electronic experts; however we need to be able to perform
some basic tests to determine the reliability of the power
provided to a computer and its components.
General Safety Principles
The PC’s power supply solves the internal power issues for the
computer, but many of the PC’s power problems are caused
by the original power source.
Although we tend to take electrical power for granted most of
the time, that is, until it is not there, electrical power can
be a very unstable, damaging force that the PC needs to be
protected against.
General Safety Principles
Electrical power tends to fluctuate in its voltage. While its
normal operating range can vary, it is usually between 95
and 125 volts. On occasion though, the current spikes above
or drops below its normal range and causes damage to a PC
that is unprotected from sudden changes in the current.
The best way to protect your PC is with a surge suppressor
or an uninterruptible power supply (UPS).
General Safety Principles
Testing electronic devices
A computer technician does not need to be an electronic
technician to test electronic equipment successfully.
Although testing at the device level does not require the
sophisticated equipment as testing at the component level,
knowing a few electronic testing techniques will be helpful.
The most important tool that you as a computer technician can
use for device testing is the multi-meter (also known as a
Volt Ohm Meter or a Digital Volt Ohm Meter).
General Safety Principles
Testing electronic devices cont’d
The multi-meter’s name is derived from its ability to measure
several different parameters.
With a multi-meter, we can test for AC and
DC voltage, resistance, and continuity.
Some meters will also allow one to test for
current as well (less than 10 amps).
We can test various electronic components
as well as the electrical power in the computer.
General Safety Principles
Testing electronic devices cont’d
Most multi-meter will consist of a digital or analog meter or
display, a pair of wires with probes (one black and one red)
and a switch for adjusting the range of settings to be
measured. The red wire is considered the positive probe
and the black wire is considered the negative or ground
probe.
General Safety Principles
The Electronic Building Blocks of the PC
Four primary electronic components are used on virtually every
electronic circuit inside the computer. These components
are resistors, capacitors, diodes, and transistors.
Resistor slows down the flow of electrical current in a circuit
General Safety Principles
The Electronic Building Blocks of the PC
Four primary electronic components are used on virtually every
electronic circuit inside the computer. These components
are resistors, capacitors, diodes, and transistors.
Capacitor is used to store electrical charges. Most of the
computer’s capacitors are small, but there are some large
capacitors in the computer that hold enough charge to kill
you, such as those in the monitor and power supply
General Safety Principles
The Electronic Building Blocks of the PC
Four primary electronic components are used on virtually every
electronic circuit inside the computer. These components
are resistors, capacitors, diodes, and transistors.
Diode forces the electricity to flow in one way only
General Safety Principles
The Electronic Building Blocks of the PC
Four primary electronic components are used on virtually every
electronic circuit inside the computer. These components
are resistors, capacitors, diodes, and transistors.
Transistor which stores a single binary digit (bit)
General Safety Principles
The Electronic Building Blocks of the PC, cont’d
Another basic electronic component found in the circuitry of
the PC is the logic gate.
A logic gate is created from a combination of resistors,
capacitors, diodes, and transistors.
Circuits are made up of logic gates and electronic systems are
made up of circuits.
Perhaps the most important electronic component in the
computer is the microprocessor. The microprocessor
controls the function of virtually all other electronic
components of the computer.
General Safety Principles
The Electronic Building Blocks of the PC, cont’d
Another component, a coil (also called an inductor), provides
resistance to AC current and no resistance to DC current.
Coils are simply wire wrapped in loops. Sometimes the wire is
wrapped around a piece of ferrous metal, and are used in
conjunction with capacitors to provide filtration when
converting AC to DC.
Failure of a coil is usually indicated by discoloration or burning
of the wires.
General Safety Principles
The Electronic Building Blocks of the PC, cont’d
Testing a coil is simple. Since a coil is made of wire, testing is
similar to a transformer: Inspect the coil for visual signs of
deterioration.
Turn the power off and do a conductivity test: Set the meter
the same as for a capacitance or resistance check. You will
need to disconnect one end of the coil before starting the
test. Put the leads across the coil and note the reading. Any
reading greater than zero indicates that the coil is not
open. This test is only an indication of whether or not a coil
is bad. To do a complete test will require removing the coil
from the part and using an inductor tester.
General Safety Principles
The Electronic Building Blocks of the PC, cont’d
Another component is the fuse. The typical fuse that is used
appears in glass tube, where the wire inside determines the
capacity of the fuse.
As the flow of current increases, heat is generated in a wire. If
too much heat is generated, a wire will soften and melt
causing a failure.
The gauge (diameter) of the wire and the material of
construction determine at what current flow (amperage)
the wire will fail. All fuses are rated in amps (A) or the
maximum current it can sustain before failure. Some fuses
are designated as slow blow.
General Safety Principles
Electro-Static Discharge (static electricity) is one of the most
damaging phenomena that occur with electronic equipment.
It is an unseen (and sometimes unheard) force that is deadly to
a computer’s components, and is oftentimes created by
humans.
General Safety Principles
Static electricity is generated when two dissimilar materials
are rubbed together.
The rubbing causes positive electrons to migrate to one
material and negative electrons to move to the other. When
the materials are quickly separated (before the electrons
have time to neutralize), one becomes positively charged
while the other becomes negatively charged.
The two materials are now electrically unstable and will
discharge its energy to ground as soon as there is an
available path (a conductor) for the flow of electrons.
The discharge of this energy is ESD.
General Safety Principles
There are two important points that you need to remember
about ESD.
First is that low relative humidity increases the possibility of
generating ESD. This is particularly true in the low humidity
environments caused by dry heat during the cool/cold
times.
The second is that ESD does not have to be seen to do damage
to electronic components; it generally takes a potential of
about 20,000 volts before ESD is actually ―seen‖ or ―felt‖,
while voltages of less than 100 can be fatal to some
components.
General Safety Principles
1.
Ways to prevent ESD
a.
Zero Potential - Make sure you and the computer are at
Zero Potential by continuously touching an un-painted
metal surface of the chassis or the computer power
supply case.
b. Standing - Standing at all times is very important when
working on the computer, as sitting on a chair can
generate charges.
d. Cords - Make sure you remove everything from the back
of the computer (power cord, mouse, keyboard, among
others).
General Safety Principles
1.
Ways to prevent ESD, cont’d
d. Clothes - Be careful not to wear clothing that conducts
a lot of electrical charges, such as a wool sweater; or
simply do not wear clothes made of synthetic materials.
e.
Weather - Try not to work on a computer during
electrical storms, storms can increase the ESD risk.
f.
Remove personal accessories - Make sure you remove all
jewellery to help reduce ESD, as they are conductors
and can also cause short circuits.
g.
Use an ESD wrist-strap -Be sure that you are using it
properly and ensuring that the resistor is good.
General Safety Principles
1.
Ways to prevent ESD, cont’d
h. Make sure that the computer chassis is grounded.
i.
Keep electronic devices in or on the protective bags
until needed.
j.
Do not place circuit boards on metal or foil.
k.
Create an ESD workstation –this consists of: antistatic mat, wrist strap, ground wire.
l.
Maintain the relative humidity, between 50 and 70
percent.
General Safety Principles
2. Never put yourself in a position where you are the path of
least resistance between the hot line and ground!
A polarized plug showing hot and neutral, and
a three-prong plug showing hot, neutral, and ground
General Safety Principles
2. Never put yourself in a position where you are the path of
least resistance between the hot line and ground!
A receptacle tester
–used to verify that hot, neutral, and ground
are wired correctly
General Safety Principles
3. Use appropriate methods/strategies to dispose of damaged
or wasted equipment/parts.
General Safety Principles
4. Preventing Lethal Shocks
It is possible to receive a lethal shock from inside a
computer (especially the monitor), voltages as high as 30,000
volts (30 KV) may exist (even after the power is turned OFF).
Thus,
 If in doubt – D O N O T A T T E M P T!
 Always use grounded outlets and power cords.
 Switch OFF and disconnect all equipment from its power
source before removing any covers.
General Safety Principles
4. Preventing Lethal Shocks cont’d
 Always replace blown fuses with the correct rating and type.
 Do not work alone - you might need help in an emergency.
 Work with one hand -using two hands can cause a direct
circuit, via your heart, from one object to another.
General Safety Principles
Protect the environment against EMI
EMI is another phenomenon that can cause electrical problems
with computers; it is caused by the magnetic field produced
as a side effect when electricity flows.

EMI in the radio frequency range, which is called radio
frequency interference (RFI), can cause problems with
radio and TV reception.

Data in data cables that cross an electromagnetic field can
become corrupted, causing crosstalk.
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Power supplies are also shielded to prevent them from
emitting EMI.
General Safety Principles
EMI affects computers mostly through intermittent errors
that may occur. Unchecked EMI will distort images on a
video display, corrupt communications equipment, and
corrupt data on floppy disks.
To solve:
•
Try moving the PC to a new location.
•
If the problem continues, try moving it to a location that uses
an entirely different electric circuit.
•
If EMI in the electrical circuits coming to the PC causes a
significant problem, use a line conditioner to filter the
electrical noise.
•
A properly grounded computer will both prevent the
transmission of EMI and protect itself from other sources of
EMI.
General Safety Principles
A simple way to detect EMI is to use an inexpensive AM radio.
Turn the tuning dial away from a station and all the way
down into a low-frequency range. With the radio on, you can
hear the static that EMI produces. Try putting the radio
next to several electronic devices to detect the EMI they
emit.
General Safety Principles
A wide range of devices on the market condition the AC input
to computers and their peripherals, whereby eliminating highs
and lows and provide backup power when the AC fails.
These devices, installed between the house current (HC) and
the computer, fall into three general categories:
 surge suppressors
 power/line conditioners
 uninterruptible power supplies (UPSs)
General Safety Principles
The proper placement or location of a computer relative to its
environment is important for ease of maintenance and long life.
This will also minimize the requirements for cleaning.
Thus, a few good practices for placement of computer
equipment includes:
 A dust-free and smoke-free environment.
 Controlled humidity (50 to 70 percent relative humidity).
 Controlled temperature (do not place too close to a heater
or in direct sunlight and avoid temperature extremes).
 Good ventilation (make sure that the fan/ventilation vents
aren’t blocked).
General Safety Principles
A fire in the workplace can be disastrous, both in terms of lost
equipment and injuries to people.
Knowing what to do in the event of a fire can save valuable
equipment and most importantly, lives.
To help prevent fire and to protect yourself:
 Always know the emergency procedures for your company.
 Know the location of the nearest fire exits.
 Know the location of the nearest fire extinguishers and how
to use them.
 Don’t overload electrical outlets.
:
General Safety Principles
Simply knowing the location of a fire extinguisher is of no value
unless you know how to use it. Additionally, using the wrong
type of fire extinguisher on a fire can be worse than not using
one at all.
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Groth, D., et. Al. (2007). PC Hardware Essentials. NJ: Wiley
Pathways
Mueller, S. (2010). Upgrading and Repairing PCs, 19th
Edition. Indianapolis: Pearson Education, Inc.
Rosenthal, J. and K. Irwin. (2004). PC Repair and
Maintenance—A Practical Guide. Massachusetts: Charles
River Media, Inc..