Television Principles and Practice J. S. Zarach Senior Lecturer. North Staffordshire Polytechnic Noel M. Morris Principal Lecturer. North Staffordshire Polytechnic M © J. S. Zarach and Noel M. Morris 1979 Softcover reprint of the hardcover I st edition 1979 All rights reserved. No part of this pUblication may be reproduced or transmitted, in any form or by any means, without permission. First published 1979 by THE MACMILLAN PRESS LTD London and Basingstoke Associated companies in Delhi Dublin Hong Kong Johannesburg Lagos Melbourne New York Singapore and Tokyo Typeset in 10/12 Times by Reproduction Drawings Ltd, Sutton, Surrey British Library Cataloguing in Publication Data Zarach, J S Television principles and practice. 1. Television-Repairing I. Title II. Morris, Noel Malcolm 621.3888'7 TK6642 ISBN 978-0-333-19221-4 ISBN 978-1-349-16124-9 (eBook) DOI 10.1007/978-1-349-16124-9 This book is sold subject to the standard conditions of the Net Book Agreement. The paperback edition of this book is sold subject to the condition that is shall not, by way of trade or otherwise, be lent, re-sold, hired out, or otherwise circulated without the publisher's prior consent in any form of binding or cover other than that in which it is published and without a similar condition including this condition being imposed on the subsequent purchaser. Contents Preface xi 1. Principles of Colour and Colour Perception 1 1.1 Colour Perception of the Eye 1 1.2 Additive and Subtractive Mixing of Colours 3 1.3 Hue, Saturation and Brightness 5 2. Transmission of Monochrome and Colour Television Information 6 2.1 The TV Camera 6 2.2 Block Diagram of Monochrome Transmitter 8 2.3 Principles of Colour Transmission 10 2.4 Colour TV Camera Arrangements 11 2.5 TV Signal Bandwidth 12 2.6 Signal Sidebands 15 2.7 Channel Allocation 17 2.8 Modulation of Colour Information 17 2.9 The PAL System 22 2.10 Other Colour Encoding Systems 23 3. The Composite Video Signal 25 3.1 The Video Signal Waveform 25 3.2 The Luminance Waveform of a Colour Bar Signal 26 3.3 Chrominance Waveforms of the Colour Bar Signal 28 3.4 The Composite Video Waveform of the Colour Bar Signal 33 3.5 The Field Synchronising Pulse Sequence 34 3.6 Teletext Information 36 3.7 Intercarrier Sound Transmission 36 4. The Essential Features of a TV Receiver 37 4.1 Introduction 37 4.2 The Tuner 37 vi Contents 4.3 The I.F. Strip 39 4.4 The Vision Detector and Video (Luminance) Amplifiers 39 4.5 The Colour Decoder 40 4.6 Sound Stages 41 4.7 The Synchronising Pulse Separator 41 4.8 The Line Time Base 41 4.9 The Field Time Base 42 4.10 The Picture Tube 42 4.11 Power Supplies 43 5. Tuners and I.F. Amplifiers 45 5.1 High Frequency Performance of Electronic Amplifiers 45 5.2 The U.H.F. Tuner 46 5.3 The Varicap Diode Tuner 48 5.4 V .H.F. and Integrated V.H.F ./U.H.F. Tuners 50 5.5 Touch Tuners 53 5.6 Remote Control 55 5.7 Tuner Servicing 57 5.8 Frequency Response of I.F. Amplifiers 59 5.9 Practical I.F. Amplifier Circuits 60 5.10 Alignment of I.F. Amplifiers 66 5.11 Automatic Frequency Control (A.F.C.) 69 6. Vision Detectors and Video Amplifiers 73 6.1 Principles of Signal Demodulation 73 6.2 Diode Detector Circuits 74 6.3 Synchronous Video Demodulation 75 6.4 Requirements of Video Amplifiers 79 6.5 Amplification of the D.C. Component 79 6.6 Amplification of Middle and High Video Frequencies 83 6.7 Luminance Stages in Colour Receivers 85 6.8 R, G, B Drive Circuits 87 6.9 Colour Difference Drive 89 6.10 Brightness Control 91 6.11 Contrast Control 93 6.12 Flyback Blanking 95 6.13 Beam Limiting 96 6.14 Typical Arrangements of Video and Luminance Amplifier Circuits 99 6.15 Automatic Gain Control (A.G.C.)-Basic Principles 101 6.16 Mean Level A.G.C. 101 6.17 Peak Level A.G.C. 102 6.18 Gated A.G.C. 104 Contents vii 6.19 Forward and Reverse A.G.C. 105 6.20 Direct and Delayed A.G.C. 107 6.21 Fault-finding in Video Amplifiers and A.G.C. Circuits 108 7. Chrominance Signal Stages 110 7.1 Processing the Chroma Signal 110 7.2 Chrominance Take-off Arrangements 112 7.3 Chroma Amplifiers 112 7.4 PAL Delay line 114 7.5 Synchronous Demodulators 119 7.6 (G'-Y') and R, G, B Matrix 121 7.7 Regeneration of the Colour Sub carrier 125 7.8 The Ident and the Colour Killer Circuits 130 7.9 The PAL Switch 133 7.10 Integrated Circuits in Colour Decoders 136 7.11 Fault-finding in Colour Decoders 140 8. TV Sound 144 8.1 Principle of Intercarrier Sound 144 8.2 Intercarrier Amplifiers and Sound Demodulators 145 8.3 Audio Frequency Amplifiers 150 9. Synchronising Pulse Separator and Field Time Base Circuits 154 9.1 Separation of Synchronising Pulses from Composite Video 154 9.2 Processing of Field and line Synchronising Pulses 157 9.3 Receiver Time Base Requirements 161 9.4 S-correction and Scan Linearity 162 9.5 Valve Field Time Base Circuits 164 9.6 Transistorised Field Time Base Circuits 171 9.7 Integrated Circuits in the Field Time Base 176 9.8 Class D (Switched Mode) Field Time Base 178 9.9 Fault-finding in Sync. Separator and Field Time Base Circuits 178 10. Line Time Base Circuits 181 10.1 line Time Base Synchronisation 181 10.2 The Line Oscillator 185 10.3 Transistorised line Driver Circuits 190 10.4 Equivalent Circuit of a line Output Stage 191 10.5 Simple Transistorised line Output Stage 192 10.6 High Power Transistorised Line Output Stage 195 10.7 Valve Line Output Stage 198 viii Contents 10.8 Generation of E.H.T. 201 10.9 Thyristors in Line Output Stage 204 10.10 Faults in Line Time Base Circuits 206 10.11 Safety Aspects of Line Time Base Operation and Servicing 208 11. Picture Tubes and Associated Circuits 210 11.1 Basic Principles of Picture Tube Operation 210 11.2 The Electron Gun 211 11.3 Arrangements for Correct Picture Geometry 212 11.4 The Shadowmask Tube-Delta Gun Version 213 11.5 The Shadowmask Tube-In-line Version 216 11.6 The Trinitron Tube 217 11.7 Dynamic Convergence Circuits-General Requirements 218 11.8 Dynamic Field Convergence Circuits-Delta Gun Tubes 219 11.9 Dynamic Line Convergence Circuits-Delta Gun Tubes 221 11.10 Dynamic Convergence Circuits-In-line Tubes 223 11.11 Pincushion Correction 225 11.12 Grey Scale Tracking 231 11.13 Automatic Degaussing 232 11.14 Tube Safety Features; Precautions when Handling C.R.T. 233 12. Receiver Setting-up Procedure 235 12.1 Fundamentals of Receiver Setting-up Procedure 235 12.2 Installation Checks on a Colour Receiver 235 12.3 Manual Degaussing 237 12.4 Purity Adjustments 237 12.5 Static Convergence Adjustments 239 12.6 Dynamic Convergence Adjustments 240 12.7 Pincushion Distortion Adjustments 242 12.8 Grey Scale Adjustments 243 12.9 Test Cards 245 13. Television Aerials and Systems 249 13.1 Properties ofV.H.F. and U.H.F. Signals 249 13.2 Fundamentals of the Receiving Aerial; the Dipole 250 13.3 Multielement Aerials 254 13.4 Special Aerial Designs 255 13.5 Aerial Feeder Cables 257 13.6 Choice of Aerial Installation 258 13.7 Aerial Attenuators 260 13.8 TV Signal Distribution Systems 261 Contents ix 14. Receiver Power Supplies 263 14.1 Power Supply Requirements 263 14.2 Heater Supplies 264 14.3 Unregulated D.C. Supplies 266 14.4 Simple Stabilised Supply Circuits 268 14.5 Switched-mode Power Supplies 272 14.6 Thyristor Regulator Circuits 273 14.7 Series Transistor Switched-mode Regulator Circuits 277 14.8 Shunt Switched-mode Power Supplies 278 14.9 Overcurrent Protection 283 14.10 Overvoltage Protection 284 14.11 Power Supply Fault-fmding and Safety Considerations 286 14.12 Mains/Battery Operation 288 Index 289 Preface The aim of this book is to present the reader with a comprehensive description of the principles involved in the operation and servicing of modern TV receivers. The treatment of the subject is such that is should appeal to students preparing for examinations of the City and Guilds Institute for Radio, TV and Electronics Mechanics. In this connection the syllabuses of the two options, Television (Colour and Monochrome) and Additional TV, receive extensive coverage. Students taking CGU Radio, TV and Electronics Technicians course, as well as the various 'television options' within the Technician Education Council framework, should also find the text of considerable assistance. Many service engineers who wish to refresh their knowledge will find the subject presented in an easy-to-follow manner. The contents of the book reflect the circuit techniques adopted in modern TV receivers; these include transistors, I.C.s, thyristors, valves (still used in many time base circuits) and other devices as appropriate. The first three chapters cover the important aspects of colour perception and the formation of monochrome and colour signals (with special reference to the PAL system). A review of a complete TV receiver in block diagram form is presented in chapter 4; this provides the basis for detailed circuit descriptions in later chapters. Chapters 5 to 7, inclusive, cover the main signal path from the tuner to the video (luminance) amplifiers and decoder. Practical circuits and principles of the inter carrier sound reception are fully outlined in chapter 8. The field and line time base circuits (including e.h.t. generation) are featured in chapters 9 and 10. This is followed in chapter 11 by a description of picture tubes, including delta gun and in-line tubes, together with information about convergence and pincushion correc tion circuits. Receiver setting-up procedures are outlined in chapter 12, including details of test cards F and G. Aerials and practical aspects of their installation are discussed in chapter 13; finally, in chapter 14 receiver power supplies are described, ranging from simple rectifier circuits to switched-mode arrangements. Throughout the book, reference is made to the practical aspects of TV servicing and to the accompanying safety considerations. xii Preface The authors wish to thank the following organisations for permission to use their technical information in this book: BBC, Decca, GEC, ITT, Mullard, Philips, Rank Radio International and Thorn. J.S.ZARACH N.M.MoRRIS