Carry out basic repairs to electronic apparatus by replacement of

56 Pages·2010·2.03 MB·English

Electrical, Electronics
Engineering Department

Carry out basic repairs to
electronic apparatus by
replacement of
components

Competency Code:
UEENEEH002B

Version No 1 2 3 4 5
Date 12/2008 05/10
Refer to: DMcR DK

Chisholm Institute of TAFE
Dandenong Campus
Stud Road
DANDENONG 3175
Tel: [phone]
Fax: [phone]

© Copyright Chisholm Institute 1
UEENEEH002B CARRY OUT BASIC REPAIRS TO ELECTRONIC
APPARATUS BY REPLACEMENT OF COMPONENTS

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© Copyright Chisholm Institute 2
UEENEEH002B CARRY OUT BASIC REPAIRS TO ELECTRONIC
APPARATUS BY REPLACEMENT OF COMPONENTS
Competency Details

Competency Title Carry out basic repairs to electronic
apparatus by replacement of components
Nominal Duration 20 hours
Competency Code UEENEEH002B
Unit Descriptor This unit deals the replacement of electronic component,
cabling an sub systems of electronic apparatus.
Dismantling and assembling apparatus and
disconnecting and reconnecting components. It
encompasses safe working practices, following written
and oral instruction and procedures, basic testing and
techniques,

Prerequisite Units UEENEEE002B Dismantle, assemble and fabricate
electro technology components

Essential Knowledge and Skills

2.18.9 Electronic safe working practices
E2.1.8 Electronic cable and conductor terminations
E2.11.11.1 Electronic soldering equipment and techniques
E2.9.1.1 Electronic component basics

© Copyright Chisholm Institute 3
UEENEEH002B CARRY OUT BASIC REPAIRS TO ELECTRONIC
APPARATUS BY REPLACEMENT OF COMPONENTS

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© Copyright Chisholm Institute 4
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APPARATUS BY REPLACEMENT OF COMPONENTS

Table of Contents

Electrical Safe Working Practices .............................................................................. 7
Electrical shock ...................................................................................................... 7
Working with De-Energised Equipment ................................................................ 10
Working on Energised Equipment ........................................................................ 11
Re-energising Equipment .................................................................................... 13
Electrical Safety Signs ......................................................................................... 14
Types and Characteristics of Cables and Conductors ............................................. 16
Definitions ............................................................................................................ 16
Types of Cables ................................................................................................... 16
Removing Insulation from Cables ............................................................................ 17
Basic Methods of Terminating Conductors .............................................................. 19
Mechanical Connection ........................................................................................ 20
Special Purpose Cables .......................................................................................... 24
Twisted Pair Cable ............................................................................................... 25
Fibre Optic Cable ................................................................................................. 26
Terminating UTP Cable ....................................................................................... 27
Soldering ................................................................................................................. 30
Detailed Description ............................................................................................. 34
Soldering Iron Types ............................................................................................ 37
Desoldering using solder wick .............................................................................. 39
Desoldering using a vacuum pump (solder sucker) .............................................. 40
Surface mount technology (SMT)......................................................................... 41
FM Wireless Microphone ..................................................................................... 47
Components ........................................................................................................ 48
Printed Circuit Boards .......................................................................................... 50
Component Assembly .......................................................................................... 51

© Copyright Chisholm Institute 5
UEENEEH002B CARRY OUT BASIC REPAIRS TO ELECTRONIC
APPARATUS BY REPLACEMENT OF COMPONENTS

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© Copyright Chisholm Institute 6
UEENEEH002B CARRY OUT BASIC REPAIRS TO ELECTRONIC
APPARATUS BY REPLACEMENT OF COMPONENTS
Electrical Safe Working Practices
Electrical shock
The magnitude and the effect of an electrical shock depend on the magnitude of the
current passing through the body, and the path taken by the current.

The most dangerous path for the current to take is that which embraces the heart (or
in unusual circumstances, the head). Usually this involves hand to hand or hand to
foot contact. (See figure 1.)

Figure 1 Contact points for electric shock
Fundamentally, current, rather than voltage, is the criterion of shock intensity and is
dependent on body resistance, contact conditions, current path through the body,
and the frequency and waveform of the current.

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UEENEEH002B CARRY OUT BASIC REPAIRS TO ELECTRONIC
APPARATUS BY REPLACEMENT OF COMPONENTS

Degrees of Electrical Shock
It is generally accepted, on the basis of a large number of investigations, that
electrical current flow through the body of the following magnitudes will generally
cause the stated effect:

a. 0.5 mA to 2 mA. Limit of perception, the smallest current it is normally
possible to detect;

b. 2 mA to 8 mA. The sensation becomes more painful;

c. 8 mA to 12 mA. Painful muscle spasm sets in;

d. 10 mA to 15 mA. This is the limit of being able to “let go”; Muscles will no
longer obey voluntary commands. For example, it will not be possible to
release the grip around a live conductor, the muscles being “frozen” stiff;

e. 20 mA to 50 mA. Such current, if passing through the chest, will interfere
with, and possible stop, breathing;

f. 50 mA to 100 mA. If passing in the vicinity of the heart, such current will
cause ventricular fibrillation (heart muscles contract in a random disordered
way). This interferes with circulation and deprives the body of oxygen;

g. 100 mA to 200 mA. Such current will stop the heart;

h. Above 200 mA (several amperes). Severe burns.

The current will be determined by the applied voltage and the resistance of the
current path.

V

I =
Ohm’s Law
R

Ohm’s Law defines the relationship between voltage, current, and resistance in an
electrical circuit.

© Copyright Chisholm Institute 8
UEENEEH002B CARRY OUT BASIC REPAIRS TO ELECTRONIC
APPARATUS BY REPLACEMENT OF COMPONENTS
Factors Affecting the Impedance of the Human Body
a. The current path
(see figure 1.)

b. The duration of current flow
The duration of the current flow is of some significance. The longer the
exposure to such a shock, the less is the victim’s chance of recovery.

Short contacts (150 ms) with alternating currents can cause ventricular
fibrillation or cardiac arrest if the contact should occur during a vulnerable
period of the cardiac cycle.

c. The voltage
Up to 50 V the value of skin impedance varies widely (even for one person)
for the factors previously mentioned.

As a conductor of electricity the human body is made up of two parts. The
upper layer of skins which has relatively high resistance, and the tissues,
muscles, etc that lie below the outer skin and have relatively low resistance.

For higher voltages (50 to 100 V) the skin impedance decreases and
becomes negligible when the skin breaks down.

d. The degree of moisture on the skin
A person with a dry, callused skin presents higher resistance than a person
with a soft skin.

For example: At 250 Vac :-
Very dry skin 2500 ohms (typ.)
Very moist skin 1000 ohms (typ.)

e. Male or Female
Generally females have a lower value of skin resistance than males.

f. The Frequency
At lower potential’s the impedance of the skin decreases as the frequency
increases so that above 500 Hz. the whole body impedance is equal to the
internal body impedance - nominally approximately 500 ohms.

Also the threshold of perception increases as the frequency increases. For
frequencies between 10 kHz and 100 KHz, the threshold rises from
approximately 10 mA to 100 mA. For frequencies above 100 KHz the tingling
sensation characteristically perceived at lower frequencies becomes a feeling
of warmth for currents in the order of hundreds of milliamperes. At these
higher frequencies there is no data on threshold of “let-go” or ventricular
fibrillation. However, burns may occur at these frequencies depending on the
current and duration of contact.

g. The surface area of contact
For larger contact areas, the initial resistance of the human body is equal to
the same as for hand-to-hand and hand-to-foot contact, ie approximately 500
ohm.
© Copyright Chisholm Institute 9
UEENEEH002B CARRY OUT BASIC REPAIRS TO ELECTRONIC
APPARATUS BY REPLACEMENT OF COMPONENTS
High and Low Voltages
A voltage of 30 Vrms (ac) or 60 Vdc is considered safe. However, under some
circumstances this may not be the case. When working with voltages exceeding 30
Vrms or 60 Vdc, precautions must always be taken.

DC and AC Voltages
For Direct Current (DC), the figures for the threshold of perception and “let-go”
current are considerably higher than for Alternating Current (AC).

DC has the tendency to “jolt” or “throw” whereas AC has the tendency to cause
muscles to “spasm” and stay in contact with the source.

Working with De-Energised Equipment
The first rule for safe working is not to work on any equipment if you lack the
knowledge and/or training regarding the equipment.

Equipment being worked on should be isolated from the mains supply. This means
unplugging or disconnecting the equipment from the mains supply. Do not rely on
the effectiveness of an on/off switch, as switches can be faulty or wired incorrectly.
It’s your life and your responsibility, so do not rely on fellow workers to disconnect
equipment.

Personally ensure that the power is disconnected and check all equipment with a
suitable testing instrument to ensure that no voltages are present after isolation has
been completed.

Capacitors
Capacitors can be dangerous because of the magnitude of their stored energy.

Effects of Capacitor Discharge

Capacitance Capacitor Volts
µF 100 1000 4000 10,000
Fibrillation
1 Unpleasant Painful
likely
Dangerous
15
fibrillation
Dangerous
20 Painful but fibrillation Dangerous
unlikely

Table 1 − Effects of capacitor discharge
After isolating the power from electronic equipment, the capacitors,
especially filter capacitors, should be discharged to earth. A discharge
of 10 joules is dangerous to life.
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