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: +61 3 9212 5200 Fax: +61 3 9212 5232 © Copyright Chisholm Institute 1 UEENEEH002B CARRY OUT BASIC REPAIRS TO ELECTRONIC APPARATUS BY REPLACEMENT OF COMPONENTS This page intentionally left blank © 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 This page intentionally left blank © Copyright Chisholm Institute 4 UEENEEH002B CARRY OUT BASIC REPAIRS TO ELECTRONIC 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 This page intentionally left blank © 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. © Copyright Chisholm Institute 7 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. © Copyright Chisholm Institute 10