RETRO AUDIO Paul Hetrelezis
ISBN 978-1-907920-58-5
www.elektor.com
This ‘hands-on’ servicing guide opens with fundamental considerations of the work space of repair and servicing. This includes a comprehensive discussion of essential test equipment and tools. Two chapters are devoted to obtaining servicing information about repair and obtaining spare parts. A key chapter is on general diagnosis and testing and includes the discussion of resistance, capacitance and inductance. These electrical properties are regularly in the mind of the repairer, so understanding of them is a key objective of this book. The next chapter is about time saving repair techniques and ensuring quality repair. The remaining chapters discuss entertainment equipment itself. Each of the chapters begins with an orderly discussion of the theory of operation and common and not so common problems specific to the equipment. All chapters conclude with a summary.
LEARN DESIGN
Elektor International Media BV
Today there is a re-emerging, nostalgic interest in vinyl records and associated music entertainment gear. With this interest, there is a paralleled market for the repair of this gear.
A GOOD SERVICE GUIDE
RETRO AUDIO
● PAUL HETRELEZIS
My passion for electronics commenced in the early 1970s. After many ventures in electronics as a teenager, such as building projects from electronics magazines, my formal education in this area began in the early 1980s through to completing a BEng in Electronics in 2001. This was supplemented by spending all my spare hours contently in my workshop repairing brown goods.
The intention of the book is to offer the reader understandings, ideas and solutions from the perspective of a workbench technician and electronics hobbyist. It is a descriptive text with many tables of useful data, servicing tips and supplementary notes of not so common knowledge.
RETRO AUDIO – A GOOD SERVICE GUIDE
A GOOD SERVICE GUIDE
Paul Hetrelezis LEARN DESIGN SHARE
SHARE
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Table of Contents
Table of Contents Chapter 1 Workshop Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 1.1 Lighting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 1.1.1 Lighting Tips . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 1.2 Organisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 1.3 Tips . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 1.3.1 General Storage Tips . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 1.3.2 Storage and management of parts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 1.4 Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 1.4.1 Electrical Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 1.4.2 Explanation of Electrical shock and its dangers . . . . . . . . . . . . . . . . . . . . . 25 1.4.3 Important note on electrical safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 1.4.4 Isolation Transformers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 1.4.5 RCDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 1.4.6 Safety Advice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 1.4.7 Other safety considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Ventilation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Eye protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 1.4.8 Electrostatic component protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 1.4.9 Electrostatic discharge Tips . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 1.5 Set up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 1.5.1 Space . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 1.5.2 Workbench set up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 1.6 Test Equipment and Tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 1.6.1 Multimeters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Analogue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 General Rules of Usage of an Analogue multimeter . . . . . . . . . . . . . . . . . . . . . . 29 Digital . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 1.7 Notes on DMM meters maintenance and procedures . . . . . . . . . . . . . . . . . . . . . 32 1.7.1 Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 1.7.2 Oscilloscopes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
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Retro Audio: A Good Service Guide 1.7.3 Bench Power supplies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 Signal Tracers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 Function Generator and signal injectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 1.8 Active and Passive Component testers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 1.8.1 Passive Component testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 ESR meters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 1.8.2 Frequency counters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 Frequency counters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 Other handy Equipment and/or job specific equipment . . . . . . . . . . . . . . . . . . . 35 1.9 Essential servicing Tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 1.9.1 Soldering /desoldering Tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 Simple Irons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 Soldering Rework stations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 Soldering accessories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 Maintenance of soldering equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 1.10 Hand tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 1.11 Further testing advice and techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 TIPS on using testing equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 1.11.1 Handy Auxiliary items: servicing aids (cleaners, glues etc.) . . . . . . . . . . . . 38 1.12 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 Chapter 2 Obtaining Spare Parts: component properties and uses . . . . . . . . . . . . . . 41 2.1 General explanation of discrete component types & parameters . . . . . . . . . . . . . 41 2.2 Passive components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 2.2.1 Resistors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 2.3 Capacitors and components with capacitive properties . . . . . . . . . . . . . . . . . . . . 43 2.3.1 Capacitors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 2.3.2 Other components with capacitive properties . . . . . . . . . . . . . . . . . . . . . . 44 2.3.3 Inductors and components with inductive properties . . . . . . . . . . . . . . . . . 45 2.3.4 Other components containing inductive properties . . . . . . . . . . . . . . . . . . . 45 2.4 Dynamic components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 2.4.1 Diodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 2.4.2 Transistors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
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Table of Contents 2.4.3 3 FETS & MOSFETS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 Integrated circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 Operational amplifiers and other common ICS . . . . . . . . . . . . . . . . . . . . . . . . . 49 2.4.4 Mechanical and hardware parts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 2.4.5 Safety tips when working on parts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 2.5 Methods to obtain replacement parts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 2.5.1 New for old . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 2.5.2 Re-used salvaged parts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 Salvaging tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 2.5.3 Methods of extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 Using wire cutters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 De-soldering technique for obtaining salvaged parts . . . . . . . . . . . . . . . . . . . . . 52 2.5.4 Tips for Desoldering parts for salvaging DIL ICs . . . . . . . . . . . . . . . . . . . . 53 Other extraction methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 Extracting parts with a propane blow torch . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 Other considerations of when salvaging parts . . . . . . . . . . . . . . . . . . . . . . . . . 54 2.5.5 Repairing parts to extend longevity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 2.5.6 Improvisation as a last choice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 2.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 Chapter 3 Obtaining source information for repair . . . . . . . . . . . . . . . . . . . . . . . . . . 57 3.1 Schematics and Service Manuals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 3.1.1 Having an identical working audio equipment to reference . . . . . . . . . . . . . 58 3.2 Circuit tracing procedures (alternative method to no schematic) . . . . . . . . . . . . . 58 3.3 Other ways to obtain information about audio products . . . . . . . . . . . . . . . . . . . 58 3.3.1 Parts identification (old/replacement parts) when no schematic available . . . 58 Passive Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 Capacitors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 Inductors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 3.3.2 Semiconductor Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 Transformers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 Speakers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 Motors and drive parts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
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Retro Audio: A Good Service Guide Fuses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 Switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 Display Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 3.3.3 Identifications of electronic circuit functions . . . . . . . . . . . . . . . . . . . . . . . 61 3.3.4 Tips on identifying rail voltages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 3.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 Chapter 4 Initial Diagnostic Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 4.1 Important Tip . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 4.1.1 Having a highly organised and methodical approach to diagnosis . . . . . . . . 63 4.1.2 Incorrect diagnosis of a fault . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 4.1.3 Procedures and ideas in correct diagnosis of a fault . . . . . . . . . . . . . . . . . . 65 4.1.4 Elimination by substitution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 4.1.5 Understanding the prognosis of repairing - Is it worth the pursuit? . . . . . . . 66 4.1.6 Customer history of audio equipment received to your workbench . . . . . . . . 67 4.1.7 Types of Symptoms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 4.1.8 Methodology to localise the fault . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 4.1.9 Specific Component tests –in circuit and out . . . . . . . . . . . . . . . . . . . . . . . 69 4.1.10 Resistors and general resistive checks . . . . . . . . . . . . . . . . . . . . . . . . . . 70 4.1.11 Checking shorts with a milliohm meter . . . . . . . . . . . . . . . . . . . . . . . . . . 71 4.1.12 Silicon Diodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 4.1.13 LEDS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 4.1.14 Zener Diode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 4.1.15 Transistors & FETs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 4.1.16 Transistor checks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 4.1.17 JFET checks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 4.1.18 Capacitors and the properties of capacitance . . . . . . . . . . . . . . . . . . . . . . 77 4.1.19 Checking Electrolytic capacitors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 4.1.20 ESR Testing of Capacitors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 4.1.21 Inductors and the properties of inductance . . . . . . . . . . . . . . . . . . . . . . . 80 4.1.22 Power Supplies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 4.1.23 Linear Power Supplies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 4.2 Battery Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
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Table of Contents Testing of batteries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 4.3 Signal Tracing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 4.3.1 ICs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 4.3.2 Note taking and tracking testing procedures . . . . . . . . . . . . . . . . . . . . . . . 84 4.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 Chapter 5 Repair Techniques and commissioning . . . . . . . . . . . . . . . . . . . . . . . . . . 87 5.1 Dismantling/re-assemble procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 5.1.1 Antistatic considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 5.1.2 Board Plugs and wiring arrangements . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 5.1.3 Liquid Spillage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 5.1.4 Board Damage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 5.1.5 General tool usage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 5.1.6 Using drivers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 5.1.7 Audio equipment veneering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 5.1.8 Heatsinking and thermal tips . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 5.1.9 Solder and its properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 5.2 Desoldering Technique for removing faulty components . . . . . . . . . . . . . . . . . . . 89 5.2.1 Clip out method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 5.2.2 IC extraction methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 5.3 Soldering technique . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 5.3.1 Final checks after the soldering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 5.3.2 Tips on soldering irons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 5.3.3 Ensuring Repair successful (soak testing) and rechecks . . . . . . . . . . . . . . . 93 5.3.4 Final reassembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94 5.3.5 Serviced equipment risk of repeat failure . . . . . . . . . . . . . . . . . . . . . . . . . 94 5.3.6 General maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94 5.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 Chapter 6 Servicing of Tuner /Home Entertainment Amplifiers . . . . . . . . . . . . . . . . . 97 6.1 The Tuner . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 6.1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 6.1.2 Radio reception . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 6.2 Analogue AM & FM Radio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
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Retro Audio: A Good Service Guide 6.2.1 Superheterodyne design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99 6.2.2 Radio Aerials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 The AM/FM aerials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 6.2.3 The tuning and RF amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 6.2.4 The mixer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 Selectivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 Local oscillator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 The IF Amplifier block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 6.3 Demodulator stage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 6.3.1 AM Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 6.3.2 FM Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 6.3.3 Stereo FM decoders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 6.4 Common Radio faults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 6.4.1 Antenna problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 6.4.2 Multipath distortion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 6.4.3 Interference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 6.4.4 Use of aerial signal attenuator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 6.4.5 RF circuit faults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 No signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 Low or weak signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 Strong overloading signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 AM/FM switching faults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104 6.4.6 Tuner systems and problems faults . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104 Tuners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104 Mechanical tuners with a dial cord . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104 Plastic toothed runners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104 Digital tuners with key scan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 Front end signalling faults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 6.4.7 IF stage Faults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 Description of IF stages and signalling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 No output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 Overloading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
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Table of Contents Instability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106 6.4.8 AGC (Automatic Gain Control) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106 General description of AGC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106 6.4.9 Detector faults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 AM Detector/ FM Detectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 Alignment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 Component replacement and screening considerations . . . . . . . . . . . . . . . . . . 107 6.5 The amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 6.5.1 Types of amplifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 6.6 Descriptions of amplifier stages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 6.6.1 Power supplies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 6.6.2 Input stages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 Signal levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110 6.6.3 The preamplifier and user control section . . . . . . . . . . . . . . . . . . . . . . . . 110 Loudness control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110 Volume control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110 Balance control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110 Tone control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110 Filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 6.6.4 The output stages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 6.6.5 Muting and Protection circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 Muting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 6.7 Common problems and solutions of an amplifier . . . . . . . . . . . . . . . . . . . . . . . 112 6.7.1 Amplifier section faults-Output stage . . . . . . . . . . . . . . . . . . . . . . . . . . . 112 IC output stages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112 Transistor and FET output stages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112 No output on one channel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112 No output on both channels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112 Other Signal Path issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 6.8 Distortion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 6.8.1 Harmonic & IM Distortion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
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Retro Audio: A Good Service Guide 6.8.2 Crossover distortion and clipping distortion . . . . . . . . . . . . . . . . . . . . . . . 114 Crossover distortion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114 Clipping distortion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114 Transient distortion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114 6.8.3 Causes and remedies of distortion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 Noise problems and interference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 6.8.4 Cables and connectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116 Instability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116 Poor Bass and Treble response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116 Bass response losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116 Final listening test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 6.9 Power supply faults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 6.9.1 Basic checks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 No Power and initial checks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 Checking Fuses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 Checking power indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 6.10 Regulation issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 6.10.1 Poor regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 6.10.2 No Regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 6.10.3 No output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 6.10.4 RFI interference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120 Ripple and Hum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120 6.10.5 Final output testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 6.11 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 Chapter 7 Cassette Deck players . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 7.1.1 The audio cassette . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 Magnetic Tape surfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 7.2 The Tape deck player . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125 7.3 Cassette Deck Motors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125 7.3.1 Servo Controlled Motor Drives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126 DC Motors (Brushed) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
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Table of Contents 7.3.2 Hall Effect motors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127 7.4 Mechanical operation – Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128 7.4.1 Drive motors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128 7.4.2 Motor speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128 7.4.3 Slip clutch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129 7.4.4 Control linkage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129 7.4.5 Capstan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129 7.4.6 Take-up /Supply reels and braking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130 7.5 User control buttons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 7.5.1 Play/Record modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 7.5.2 Fast-forward/Rewind . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 7.5.3 Search Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 7.5.4 Pause . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132 7.5.5 Load and Eject . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132 7.5.6 Auto stop detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132 Mechanical detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132 Electronic detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132 7.5.7 Cassette-in detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 7.5.8 Tape type Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 7.5.9 Tape counters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 7.5.10 No Record protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 7.6 Electronic operation – Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 7.6.1 Tape heads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135 7.6.2 Equalization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135 7.6.3 The record signal path . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136 7.6.4 The play signal path . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136 7.6.5 The Erase Head . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136 7.6.6 Record and playback switching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137 7.6.7 VU meters and recording levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137 7.6.8 Noise Reduction circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137 7.7 Mechanical related faults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137 7.8 Motor faults - general . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
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Retro Audio: A Good Service Guide 7.8.1 Symptom: Poor motor torque . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138 Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138 Possible causes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138 7.8.2 Symptom: Motor Speed too fast or slow . . . . . . . . . . . . . . . . . . . . . . . . . 139 If a motor speed is running too fast: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139 If a motor speed is running too slow: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139 7.8.3 Symptom: Motor creating electrical noise . . . . . . . . . . . . . . . . . . . . . . . . 139 7.8.4 Symptom: Worn top bearing of motor . . . . . . . . . . . . . . . . . . . . . . . . . . 140 7.8.5 Capstan and pinch roller drive assembly . . . . . . . . . . . . . . . . . . . . . . . . . 140 7.8.6 SYMPTOM: Faulty Capstan Motor creating mechanical noises . . . . . . . . . . 140 7.8.7 SYMPTOM: Faulty or poor quality cassette tape . . . . . . . . . . . . . . . . . . . . 141 7.8.8 Brakes replacements and adjustment . . . . . . . . . . . . . . . . . . . . . . . . . . . 141 7.9 Electronic related faults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142 7.9.1 Switch problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142 Bias Oscillator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142 Erase faults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142 Audio circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142 Noise reduction fault failures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143 Search systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143 Record playback switching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143 7.10 Care and Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143 7.10.1 Audio cassette . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143 Cassette Deck player . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144 7.10.2 Play/Record Head maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144 Cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144 Checking head wear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144 Head Replacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144 Head alignment and adjustments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145 Head Demagnetising . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145 7.11 Repairing Idler wheels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146 7.11.1 Belt replacements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146 Electrical adjustments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146
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Table of Contents 7.12 Maintenance of the compact cassettes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147 7.13 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147 Chapter 8 Repairing turntables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149 8.1 Description of the turntable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149 8.1.1 The Turntable motor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151 8.2 Induction motors (brushless) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151 8.3 The platter (or phono table) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152 8.3.1 Platter Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152 Speed selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152 Platter speed adjustments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153 8.3.2 The Tonearm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153 Tonearm settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154 8.3.3 Cartridge and Stylus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154 Ceramic (or Piezo) and Magnetic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154 8.3.4 The Stylus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156 8.3.5 Turntable suspension . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156 8.3.6 The Platter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156 8.3.7 The Dust cover . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157 8.4 Common Turntable faults and maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . 157 8.4.1 Motor faults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157 Idler wheels and belts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157 Speed Selection and adjustment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159 Wow and Flutter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159 Common tonearm & cartridge faults and maintenance . . . . . . . . . . . . . . . . . . 159 8.4.2 Sound faults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160 Weak or no sound on one or more channels . . . . . . . . . . . . . . . . . . . . . . . . . 160 Hum and interference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161 Distorted sound . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161 8.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161 Chapter 9 Repairing CD players (CDPs) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163 9.1 The CD player – A general operational description . . . . . . . . . . . . . . . . . . . . . . 163 9.1.1 Reading the CD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164
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Retro Audio: A Good Service Guide 9.1.2 Focus servo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164 9.1.3 Tracking servo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164 9.1.4 Carriage servo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166 9.1.5 The RF amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166 9.1.6 The Decoder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166 9.1.7 Digital Filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166 9.1.8 Digital to Analogue conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167 9.2 Faults with CD Players . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167 9.2.1 Initial Checks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167 Prior tampering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167 Checking the Objective Lens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168 Procedure in Lens cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168 Power Supply Checks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168 Initial system controller checks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168 The Compact Disc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169 Disc Loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169 No Disc Spin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170 No Playback . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170 Start/Stop disc Rotation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170 9.3 Playability faults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170 9.3.1 Skipping or Jumping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170 9.3.2 Search and erratic behaviour faults . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171 9.3.3 Sound faults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171 9.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171 Chapter 10 Speaker & Microphone Repairs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173 10.1 Speakers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173 10.1.1 The speaker enclosures or boxes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173 10.1.2 Moving Coil Speaker Driver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173 The frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174 The magnet assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175 The voice coil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175 The suspension system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175
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Table of Contents The cone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175 10.2 Speaker Driver Faults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175 10.2.1 Moving Coil Speaker driver faults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175 10.3 Summary of speaker faults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176 10.4 Microphones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177 10.4.1 The condenser microphone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177 10.4.2 Dynamic Element microphone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178 10.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179 Appendix A Common audio connectors and pinouts . . . . . . . . . . . . . . . . . . . . . . . . 181 Appendix B Additional Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183 Appendix C Safety Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187 Appendix D Understanding 'Pit' and 'Bump' . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191 Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193
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Chapter 1 • Workshop Considerations
Chapter 1 • Workshop Considerations I consider there to be four mandatory working conditions for the workshop. They can be summed using the anagram LOSS and if you don’t apply these, it could be your LOSS!: Lighting Organization Safety Setup How a technically inclined hobbyist sets up his workshop is arbitrary, but having said this, the use of an economic environment, both from a materials and energy source perspective can be easily reached and left to the ingenuity of the individual. Many websites offer considerable resource on ways of establishing your workspace.
1.1 • Lighting There are a host of ways to light your workspace. I personally employ a mains LED lighting globe system that uses 3-10 watts per globe and provides equivalent lighting to 40 to 100 watts of incandescent globes. Although initially more expensive, the lifespan and economy of LED globes far exceeds that of incandescent or other types.
1.1.1 • Lighting Tips •
To achieve more directional lighting from a lamp, it should be positioned on the left upper side of the workbench for a right handed technician and vice versa for a left handed operator. This is because the light will reflect off the work and will not cast a shadow from the working hand over the work.
•
In this modern age, vastly more powerful and economical lighting is available with super LED lighting being a popular choice. This type of lighting can be operated from a low voltage source and combined with solar panels and rechargeable batteries.
•
I find magnification aids with light assist me greatly. A very popular variant of this is the circular fluoro light with a magnifying glass located in the centre.
1.2 • Organisation Organisation improves work procedure efficiency and hence saves time. Organisation comes in many forms, not just having neatly sorted components in trays and tools arranged in their respective places. Organisation can be seen as how you will approach or forward plan a project, be it a repair or testing, ensuring you have readily available stock parts and tools to do the job. Over the years, I have discovered the value of organisation. For example, when initially beginning to work on repairing as a young person, in a few instances it took me longer to find the reassembly fasteners of the repaired item than the time it took to repair the item itself.
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Retro Audio: A Good Service Guide
1.3 • Tips 1.3.1 • General Storage Tips --
Use labelled jam jars and other screw lid containers to mount on the underside of shelving as an economical way to store spare parts
--
Use colour coding (e.g. stickers) as an easy way to recognise the location of parts, tools and cables. This system is particularly useful when you have many trays of parts to set up in your work space. Remember not to use too many colours as this will defeat the purpose of simplification. Personally I use 4 colours (Red, Green, Blue and Yellow). More specifically, for my precision drivers, blue for flat blade, red for Phillips, green and yellow for respective miniature spanners and hex socket drivers.
--
Having a white bench-top not only provides better lighting through (reflections), but enables you to quickly locate and recognise parts or tools.
1.3.2 • Storage and management of parts --
Screw back the fasteners into the underlying chassis after dismantling outer housings of repair product.
--
Make a habit (when finished) with any item, be it a tool or other item to put it back in its respective storage spot.
--
Magnetic materials are particularly useful when trying to maintain loose small parts such as fasteners. These come in many forms including as a wristbands with a magnetic dial plate.
--
Using recycled plastic receptacles from food and other packaging products assists in easy component management and other purposes such as glue mixing trays (see Figure 1-1 on page 24)1.
Figure 1-1 Reusing plastic packaging for storage of parts
This is an economical practice to the audio product repairer and the environment
1
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Chapter 1 • Workshop Considerations
1.4 • Safety 1.4.1 • Electrical Safety It is assumed that the reader of this text has a good understanding of electricity and its lethal consequences upon failing to adopt correct procedures and Workshop practices. Most of the brown goods I have worked on have electrical safety warning stickers and I see this factor as the most important to be adhered to. Most of my close-calls have occurred because I wasn't concentrating or simply not being aware of what I was doing. They all happened within my first couple of years when I began to work on mains voltage equipment.
1.4.2 • Explanation of Electrical shock and its dangers Regardless of what measures are put in place, complacency shouldn’t arise due to these measures. Ultimately correct and rigorous procedures should be autonomous to the service person. It is important to know that is not voltage that can be lethal or cause serious injury. It is in fact current (as little as 20 milliamps or 20/1000 of an amp). A very easy way of understanding this is by using ohms law: I (Current through body) = Voltage (touched by body) / (Resistance path of body to ground). Where resistance is the conductive path through the human body Voltage is the potential of the live wiring that the person has inadvertently touched. Current is the rate of electrical flow of electrons through the path of the body.
Figure 1-2 How electrical current can flow through the body. Important note: This is a 120 volt system and for demonstration purposes only. Many countries adopt a more dangerous 220/240 volt system. It can be seen from the above relationship there is a clear, direct correlation between voltage and current. The higher the voltage, the more current will travel through a resistive path to ground such as a human body. Furthermore to the above formula, the resistance of the electrical path that a human body offers to ground for a nominated voltage would be different for each particular situation. For example a barefooted person touching live wiring with wet feet (or hands) would offer much less resistance to ground and hence greater current flow than that of a person in the same situation wearing
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Chapter 2 • Obtaining Spare Parts: component properties and uses
Chapter 2 • Obtaining Spare Parts: component properties and uses 2.1 • General explanation of discrete component types & parameters Spare parts for a repair job are paramount in the fixing of it. The part/s to be replaced ideally should be of at least of a substitute or replacement value in terms of all its characteristics: this is in cases where the exact duplicate part cannot be obtained. At design stage level, components have been selected so as they fit the purpose or requirements of the circuit function. For example, a capacitor not only needs the correct capacitance e.g. 22uF value, and correct physical construction e.g. PCB board mount against pigtail, but also the correct voltage and temperature ratings. More specifically, incorrect temperature and voltage ratings could damage the capacitor. In extreme cases, electrolytic capacitors could explode if reversed the incorrect way i.e. the negative (-) terminal to the positive side of a circuit and vice-versa. As seen in the above example, the understanding of the electrical characteristics and other properties of an electronic component is vital. This understanding is very helpful in the correct selection of replacement parts or substitution. The next subsection of this book briefly reviews the characteristics and properties of discrete prime or widely used electronic components within audio equipment. Further detail on component properties will be provided in Diagnostic Testing (see Chapter 4 on page 63) Testing), particularly that of capacitors and inductors. The reason for the emphasis on the properties of these particular parts is that they are most difficult to understand - at least from my own and other colleagues experiences. Due to the multitude of electronic parts available on the market, again this chapter will focus on those encountered in audio repairs and more specifically the ones most likely to fail over time. These components too potentially have a domino effect that will cause the failure of associated parts electrically connected to them. For example, if a transistor circuit with a series collector resistor was to become faulty and short between collector emitter junctions, the transistors collector resistor having a higher enough supply voltage could well burn out the resistor. Note that the dynamic components (semiconductors) that are most likely to fail over time (generally speaking only) are those exposed to higher switching voltages, hence currents combined with high frequency switching currents. It is worth noting that because the equipment dealt with in this text is typically built decades ago, components will have a limited lifetime today. The lifetime of these aged components is dependent on the equipment usage and conditions, both external and electrical.
2.2 • Passive components 2.2.1 • Resistors Resistors are manufactured in many forms from simple ¼ watt PCB board mount resistors to log (logarithms) potentiometers acting as volume controls for an amplifier. The primary parameters to consider here are the wattage and tolerance rating used for the purposes of this book. More to the point, any replacement component has to at least match the wattage and tolerance of the replaced resistor. For example, if a resistor with a 1 watt rating and at 5% tolerance is replaced, then above that wattage (size of resistor permitting) with a more precision rating would be an appropriate replacement. On the contrary, a ½ watt with say 10% tolerance substituted resistor would not be suitable. Typically a resistor is rated at twice its nominal (in usage under
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Retro Audio: A Good Service Guide normal conditions) wattage when used in circuitry to allow for “headroom” to prevent overheating and subsequent burnout. The tolerance (or accuracy of rating) can vary 10% to 1% e.g. precision resistors dependent on how the resistor is used and also in the quality of specification of design. For example, high precision resistors would be employed in circuits that are temperature sensitive or used for calibration purposes. An example of this is where resistors having typical positive temperature coefficients need to be stable in ohm value so as not be affected by varying ambient temperatures.
Through hole resistors
Slide Pots
Trim Pots
Rotary Pots
Figure 2-1 Examples of some commonly used resistor types in audio circuits Table 2-1 Types of Resistors Type
Physical description
Properties
Typical circuit applications
Typical ranges
Through hole resistor – Carbon Film
5 colour banded (for value) board mounted resistor. Typically brown coloured coating.
Highly used resistor with relatively moderate precision
In most circuit applications and offers a broad range of values from typically 1 ohm to many mega ohm
1Ω to 10 MΩ
Through hole resistor- Metal Film
5 colour banded (for value) board mounted resistor Typically blue coloured.
High precision resistor
For applications requiring accuracy e.g. in circuit designs where the value requires to be used as a reference.
1Ω to 10 MΩ
Through hole resistor-
Bulky rectangular shaped with value printed on white coloured and contrasted surface.
High wattage and respective lower resistor range (only to a few kilo-ohm)
Applications that the currents are relatively high. e.g. as a current limiter to a collector load or power supply applications
3W range: 0.1Ω to 10 kΩ 7W range: 0.1Ω to 7 kΩ10W range: 0.1Ω to 4.7kΩ
High power Wire Wound
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Chapter 2 • Obtaining Spare Parts: component properties and uses Type
Physical description
Properties
Typical circuit applications
Typical ranges
Standard
Single Rotary (spline or ‘D” shaft shaped). PCB board mount
Linear of Log scaled with rotation of shaft
Volume, balance, and tone pots for preamplifiers
1KΩ to 2.2MΩ
Adjustable Turn e.g. 10 turn, Mini Horizontal or vertical trim pots
Adjustable for setting
For pre-settings of motor speeds 50Ω to 5MΩ Pre-set pots
50Ω to 5MΩ
Potentiometers
Sub miniature
2.3 • Capacitors and components with capacitive properties 2.3.1 • Capacitors Capacitors too have a large family of various types. Each type is designed for a specific function such as the bipolar electrolytic. These are used in power supplies or acting as coupling capacitors between the stages of an amplifier. They are made from different materials and constructed as such to serve their intended purpose. The parameters to consider here in their usage are temperature rating, voltage rating, whether polarised (requiring orientation) or bipolar (can be orientated either way in circuit). Of course, each capacitor type is manufactured in a way to suit certain circuit functions and all have a specific limited range of offered values to suit those functions. For example, electrolytic capacitors can provide high capacitance (typically expressed in μF) whereas Ceramic capacitors are very low value range capacitors typically express in nanofarads (nF).
Figure 2-2 Examples of some commonly used capacitors in audio circuits
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Chapter 3 • Obtaining source information for repair
Chapter 3 • Obtaining source information for repair In any service repair of whatever audio equipment type, particularly complex circuitry containing respectively numerous discrete components, a schematic diagram is essential for successful and effective repair. A schematic diagram is a not only a descriptive translation in terms of proper circuit operation to assist you to locate faults, but measurements (both DC and signal) you would be expecting to read at these fault locations to confirm the fault does lie there. So it makes for a relatively fast process of diagnosis. It also assures the repairer and prospective customer that once the fix has been applied, the chance of repeat failure is very unlikely. This may not always apply to intermittent faults, but if the fault is able to be induced, then the distinct advantage of a schematic to effective repair is valuable. The reason being is the exact determination of the fault can be verified by a schematic. Given that information is not always available and will vary by manufacturer, other ways can be helpful. One effective way in audio equipment repair is to focus on limited makes and models of this type of equipment. The first part of this process would be to attempt to obtain as many service manuals and schematics as possible for a preferred and popular make and model of equipment. The make would have to be popular so as not limit your obtainability of this equipment. Once obtained, faults can then be methodically identified, repaired and logged in order to build a good knowledge base. This will provide you with an understanding of the faults that tend to occur with these makes and respective models. If the fault is a common trade fault, then industry service personnel could well help. The audio equipment reviewed in this book is of a past era and hence faults, be it production or modification errors have more or less all been identified. There are numerous online resources of information at circuit level, forums and websites for specific types of servicing - the information is virtually limitless. Faults too are limitless in the sense that technically one or more discrete components of audio equipment could fail together with countless combinations of these. Past periodicals specializing in repair or electronic magazines have columns dedicated to HI-FI repairs. These can be invaluable if the symptoms and respective repairs written about pertain to your audio equipment symptoms and faults. These periodicals can be obtained from many public and educational institutes that can provide either or both softcopies and hardcopies of this information. The only issue in accessing the abundance of information available, is the difficulty in tracing specific information. Despite having fault information at hand, it is always worthwhile to reference a schematic or service manual. A fixed fault could recur again due to other influences such a required modification. These modifications of the past era were provided to the service industry by the manufacturer. The modifications involved component changes to the circuits as recommendations for a common fault that required a design solution. Also for each repair fault there will be tendencies or a likelihood for a particular circuit component failure over others. This could be age related wear such as that of a mechanical switch or turntable belt slipping. Compare this to a ¼ watt resistor used in a low voltage circuit (most unlikely to fail).
3.1 • Schematics and Service Manuals Service manuals are the most essential of all data pertaining to any form of electronic servicing. This is information provided by the manufacturer. The job in hand can be tackled with the biggest advantage as these service manuals typically not only provide circuit layouts and components listings, but other sometimes mandatory information. This information might describe safety procedures, disassembly methods, expected test signals or patterns from descriptive test procedures.
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Retro Audio: A Good Service Guide
3.1.1 • Having an identical working audio equipment to reference If you are fortunate enough to have an identical working piece of audio equipment to that you are going to repair, this is a marked advantage and second best to having a circuit diagram. Measured resistances, voltages and currents of the working unit can be compared directly to that of the faulty unit. When adopted, this point against point checking, it is best to take a methodical approach to it - first check supply voltages and any other voltage feeds to the circuit. Also check possible test points with marked voltages on the boards of the circuit being repaired or overviewed.
3.2 • Circuit tracing procedures (alternative method to no schematic) The tracing of circuits is a refined skill that requires practice, patience and much observation. This can be achieved with a reliable working continuity (or buzzer). Also required is a large notepad, pencil and eraser. The procedure I have adopted is to start at one nominated soldered point on the underside tracking any component of the suspect board to repair. From there visually trace the PCB tracking to other connecting points on the board. It can be electrically confirmed with an audible buzzer (or visual buzzer if preferred) that a connection is present. Then from these new end points, further points of connection to other components can be determined. It is worth noting the read values of components of the board. These are marked next to the drawn component as a point of reference. After scribing the connecting points to paper, a series of drawn joining lines and components will firstly appear disorganised. After a manageable number of components are drawn (say about six or so), it requires the arranging of components to replicate a recognisable circuit. This could be difficult if the reader has limited understanding of how circuits are generally configured with other components to form a circuit function or building block. There is also the option of using the “Rats nest sort feature” available as freeware to perform this unravelling and composing of a readable circuit.
3.3 • Other ways to obtain information about audio products 3.3.1 • Parts identification (old/replacement parts) when no schematic available The following sections identify discrete components that have a higher need for replacement or at least have common usage in the audio circuits covered in this text. Of course not every encountered component associated to so many repairable items can be covered in this chapter. Passive Components For passive components such as resistors, capacitors and inductors, in most cases they can be easily identified. The value of components can be determined by colour coded or numerical markings and type by their physical appearance. (See Appendix B on page 183). Resistors more than likely will go open circuit and if burnt severely enough because of overheating, will become unrecognisable in value. To replace a damaged resistor of equal value, the first requirement is to identify what value is to be replaced. There are two convenient methods to determine the value of a resistor that has been extensively damaged and consequential unrecognisable in value. 1. Remove the suspect resistor from the connecting circuit 2. Using a sharp utility knife, carefully scrape away the outer coating of the burnt resistor to expose the resistor coiled tracking.
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Chapter 4 • Initial Diagnostic Testing
Chapter 4 • Initial Diagnostic Testing The first sections of this chapter will look at diagnostic testing. The latter sections will then be more specific to component testing. Every fault you tackle for any make and model of audio equipment is unique in the sense of it as a whole. More specifically every piece of audio equipment has its own history of use - The hours it has been used and the environment it is used in and how it is operated, cared for and maintained by it's owner. Considering this, fault finding can be quite involved with the variation of faults seemingly endless. When taking on any repair, be it for yourself as a hobbyist to repair your own personal audio equipment from the past or as a small business, much consideration must be given. With experience this becomes easier and more effective. I cannot emphasise enough from the position of initial diagnosis, how important it is to understand the repair you take on and whether it is worthwhile. Many key factors play a part in this decision including having the correct and mandatory servicing equipment. Also service information is virtually mandatory. The previous chapter highlighted having adequate service information to perform the repair of audio equipment. Part availability also plays a mandatory part as does having the adequate skill to perform the repair. For example, the skills required to re-align an audio head of a cassette player differ greatly to replacing a capacitor on a board. From the initial assessment of audio equipment, you are able to get a reasonably accurate idea of the magnitude of the fault(s) within the device. To get this wrong will involve a great deal of time and effort without much gain. In a business sense, this is not an acceptable practice and may be the reason to why a “one man band” engineer may adopt a specialised repair in a limited number of makes and models of audio equipment. The disadvantage of this approach is that you limit your marketability to repairs, hence will have a direct impact on your potential customer base.
4.1 • Important Tip In any fault finding situation, never discount any component or fault causing scenarios (within reason of course). A far superior approach is to think it may be possible. Then through testing, verify the possibility with a resultant elimination or cause of fault. Remember to start at the most likely cause and work from that basis.
4.1.1 • Having a highly organised and methodical approach to diagnosis When diagnosing a fault, a general understanding of the operation of the faulty audio equipment goes a long way to at least localising the fault and possible suspect components. A good example of this is weak sound from only one speaker of a stereo cassette player. The understanding of the two symptoms: weak sound from one speaker is strongly indicative of a misaligned tape head. Understanding signal pick up from the cassette head is part of understanding the operation of the cassette player as a whole. Depending on the audio equipment and respective fault, a particular order of testing should be adopted. An example of this is an amplifier that has no audio output, only a hiss from the output its speakers. The hiss varies in loudness with the volume control. This control is located in the preamplifier circuit of the amplifier. A signal probe would be at the base of each amplifier stage starting from the front end and working backward to the preamplifier. It could be safely assumed that the power is being supplied due to the hiss from the pre amplifier volume pot. It also could be said the problem lies past the preamplifier stage as the loudness of the hiss can be controlled by the volume control (or pot).
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Retro Audio: A Good Service Guide
4.1.2 • Incorrect diagnosis of a fault Many books on electronic servicing tell of various ways to diagnose and repair faults. There should be emphasis too on the ways not to approach diagnostic servicing. These misappropriated approaches may appear to be viable at face value. Behind a seemingly sensible approach, there are hidden issues of incorrectly recognising the symptoms and/ or respective faults. This leads to many hours of wasted time and frustration. The following paragraphs will discuss the main issues I have encountered over the years of electronic fault finding. Note that the majority of these faults were encountered when I first started electronic servicing in the 80's. Beware of red herrings, they're a real trap. These diversions in diagnosis are potential time wasters. With experience they will occur less. Thinking out the problem in hand with a methodical approach will certainly reduce the time in localising a problem. This again stresses the importance of having a schematic diagram. If a schematic cannot be obtained for practical reasons e.g. time in obtaining due to limited availability, then understanding of the basic operation of the faulty audio equipment will assist greatly. An example could be a cassette and AM/FM radio product that only has audio on the left or right channel speaker on cassette playback. However when the FM radio is playing back, clear stereo sound can be heard on both channels - the indication is that the problem is with the cassette player. Is the audio cassette player play head incorrectly aligned? Due to the fact that both the cassette player and radio share the same audio amplifier and the radio is OK, this immediately eliminates the amplifier being at fault. One common pitfall is to be convinced that a component is faulty from circuit readings. A very good example of this is doing passive (no power supplied to the circuit) tests of perhaps a transistor or diode which indicate a shorted junction. After removing the component it reads OK. Resistors or capacitors paralleled to these junctions obviously influence the reading. The current from the meter probes will flow into other parallel networks. In the case of a larger value capacitor, it will charge from the meter current again giving false representation to what would be expected. Another pitfall is assuming only one component is faulty. The faulty component is replaced, and then it fails again. Why? One or more components that are also faulty are causing this. A good example of this is when an output audio transistor is replaced with a shorted junction, yet it's driver (also shorted) wasn't replaced. Other pitfalls are presuming the symptoms are specific to a certain defective component or circuit and then spending much time to trying to locate defective components that are actually in correct working order. Not so common issues could be fixing the initial fault, but creating new ones through disruption of the circuitry. This disruption could be caused in many ways. It could be due to handling of the board which has caused static damage to other previously good and working static sensitive components. It could also be caused by simple things such as not replugging board connectors to allow proper contact. It is best to always clean plugs with switch cleaner to allow full surface contact. On the mechanical side, when replacing mechanical parts such as cassette heads or drive motors, ensure that alignment and settings for these devices are correct. For example a misaligned cassette/records head can cause of a range of sound issues on playback. In all the above scenarios what is required is what I like to term an “anchor point”. This is having a definitive fault, recognising it and fitting in with all symptoms. These faults will become more easily recognisable to you over time with good experience and subsequent understanding. Correct and effective fault diagnosis cannot be easily learned by any person who has not this prior experience. However, texts such as this can provide ● 64
Chapter 5 • Repair Techniques and commissioning
Chapter 5 • Repair Techniques and commissioning Having covered some of the fundamentals of diagnostic testing, this chapter will now cover actual repair and work techniques to fix identified faults. Although fault finding can be the most challenging of tasks, it is worth noting that good repair techniques not only offer quality work, but the chance of recall being low on the work performed.
5.1 • Dismantling/re-assemble procedures When dismantling any type of audio equipment, care must be taken to reassemble it in the exact state it was, prior to the repair. It is very easy to misplace a single screw amongst many dislodged during dismantling and perhaps very time consuming when trying to relocate it. This is where you need to track your disassembly through stages. A mobile phone camera is an ideal tool to do this by taking pictures of disassembly. The pictures will have visibility of board component orientation, plugs, leads and any other visual information that may require reference at the reassembly stage. Also pictures of mechanical assemblies of say a cassette deck can be quite valuable where there is a need for replacement and reassembly of mechanical parts. An easy way to keep track of fasteners is to reinsert them into their respective threaded positions after removing the fastened part. Another way is to keep the fasteners and other dissembled parts in a labelled container e.g. a jam jar noting where they belong.
5.1.1 • Antistatic considerations The objective of anti-static protection is to ensure your body, the connections to the static sensitive device and working soldering iron are all at the same potential. This can be done through wrist strapping or utilising an antistatic mat that the electronics being repaired can rest on. A conductive floor mat can too be used under the work bench. Other precautions include keeping the static sensitive device within its protective packaging until it is used. These precautions should be adopted for the suspect device to be removed and a new one replaced. Also take note in some cases the suspected part may not be damaged. By not applying static safety handling measures confuses the issue of identifying the damaged parts, in this case. If solder pumps are used, ensure anti-static tips are used.
5.1.2 • Board Plugs and wiring arrangements When removing board plugs, prior to dislodging them their respective board sockets, be aware of what type of clip has been used. Over gripping and trying to release the plug with over exertion can cause undue strain that could create a connecting wire of the plug to become disconnected. Depending on the design of the plug socket arrangement, pulling them out by hand may not be possible. A clip on the plug may need to be levered or prised prior to removing from the board. Also how the wiring was arranged within audio equipment prior to disassembly - it should put be back the same way.
5.1.3 • Liquid Spillage Liquid spillage, if not localised can be a potential issue in terms of the repair. Spillage if left uncleaned over a period of time will cause corrosion. If the problem is in a localised area, then all components of that area should be replaced. Mechanical parts are particularly susceptible to spillage and should be carefully examined and replaced. In these cases, ensure all parts have availability for replacement. It is left to the discretion of the repairer if they wish to embark on taking up this type of repair as there are no
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Retro Audio: A Good Service Guide guarantees to a successful outcome.
5.1.4 • Board Damage If a board has been damaged, depending on the scale and type of damage, generally they are salvageable. For charred boards, these can be cut out and cleaned for safety reasons and board connectors can be re-joined using an insulated bridging connector. Any connecting or re-joining of tracks performed on the underside (soldered side) of a board should always be done so with the use of spaghetti sleeving or insulated wire. Likewise on the component side ensuring the use of at least the same gauge of wire to allow for the current capacity of the damaged track. Cracked boards can be fixed by gluing Paxolin pieces for rigidity. Epoxy resins are a good choice of adhesive.
5.1.5 • General tool usage Every tool used needs to be the correct one for the work or repair. Never take short cuts by using the incorrect tool. This includes being undersized or oversized for the task. New innovative tools are always arriving on the market and they are generally not too expensive. Therefore it is handy to have a wide range of tools and accessories available as there will likely be a chance you will use them some time in the future. Their specific use will depend on the diversity of work you perform. This preferred range of tools and servicing accessories will give you quick access at the time of need. This will not only provide for a faster turn around time for repairs, but improve quality by having the right tool for the right job.
5.1.6 • Using drivers When unscrewing a fastener, not only the correct size driver should be used but correct type. For example a Philips head looks very similar to a posi-driver head. There are different types of drivers, but the one I typically use is ratchet driver and I have a case of various sizes and types of drive bits. I also have a quality precision driver set containing popular Slot, Philips, Hex and Torx drivers. These are made of tempered steel and work well with small mechanical assemblies in cassette and CD players. When removing tight fitting fasteners, twist the driver clockwise very firmly only allowing as minimal movement as possible then unscrew in an anti-clockwise direction. If this isn’t successful then apply a short burst of freeze spray preferably using a spray tube directly at the fastener head. This may loosen it. Overall, regardless of the technique, it best to apply patience as once the fastener head becomes too burred, it may require drilling out then being rethreaded for a new replacement fastener. This drilling procedure could cause more damage if not performed carefully. The key here, as with all repair work is to carefully consider the options of resolution and carry them out carefully.
5.1.7 • Audio equipment veneering Any audio equipment housed in a wooden cabinet should be repaired, particularly if the damage could incur potential danger. Any trimmings or veneering can be re-joined using hot glue from a gun. General epoxy resin glue is very useful for these purposes. Damage to a cabinet will occur where there is the most mechanical stress occurring due to weight and leverage. Door and lid hinges as well as underside castors are vulnerable to breakage. Also glass fittings should be replaced with matching hinges in the event of the original hinge spring tension not being correctly set.
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Chapter 6 • Servicing of Tuner /Home Entertainment Amplifiers
Chapter 6 • Servicing of Tuner /Home Entertainment Amplifiers The amplifier is common to all sound systems in some form be it as a standalone unit or part of an integrated part of a sound system. There are many examples of the latter application in portable music equipment such as radio/cassette decks. The purpose of the amplifier is to amplify weak audio signals from a source such as the phono cartridge of a turntable. This type of audio source is well below a voltage level that can be directly sourced to a speaker or headphone. The amplifier also controls the audio signal. The amplifier can be separated into two functional operations: the preamplifier and power amplifier. The preamplifier preceding the power amplifier can be described as a voltage amplifier and increases the level of source signal. Through this amplification, it also acts an equaliser and controls the source signals volume loudness, selection of signal source, bass and treble controls and channel balance. The power amplifier increases both the voltage and current to provide power ranges from 10 to over 100 watts per channel. This audio is maintained at very low distortion levels and maintaining other qualities of the source music such as broad audible frequency response and dynamic range. The tuner in many pre-2000 composite audio equipment products was combined with either a cassette player and/or amplifier. Full composite systems would also incorporate a turntable. The amplifier would be common to these sound sources. This system had auxiliary inputs for the allowance of externally sourced sound such as a turntable and its output was provided by external speaker sockets. Tuners (or radios) will be reviewed first before describing amplifiers later in the chapter. This chapter will review the tuner and amplifier by providing a functional diagram of the basic building blocks. Furthermore it will describe how they fit together for overall functionality. No text reference can cover all conceivable faults for a specific component of audio equipment e.g. the amplifiers of an audio system let alone the sound system as a whole. The best compromise is to focus on the most common or vulnerable of faults seen in each of these components. This and the remaining chapters provide concise workshop reference. Combining this generalised approach on faults together with the diagnostic testing provided in Chapter 4 on page 63 is good alternative of reference. Figure 6-1 provides a simplified view of the main sections of a combined amplifier and tuner unit. OUTPUT TO TAPE ANTENNA
AM/FM TUNER SIGNAL SOURCE SELECTOR
AUX PHONO
EQUALIZER
POWER TO ALL SECTIONS
120 VAC
TAPE MODE SWITCH
INPUT TO TAPE
TONE LOUDNESS VOLUME FILTERS BALANCE
POWER AMPLIFIER
OUTPUT TO SPEAKERS
PREAMPLIFIER
POWER SUPPLY
Figure 6-1 Block diagram indicating main sections of a tuner amplifier unit
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Retro Audio: A Good Service Guide
6.1 • The Tuner 6.1.1 • Introduction Radio could be considered another entirely separate branch of discussion in audio. However due to radio receivers being an essential item in audio Hi-Fi systems, it will discussed in the first part of this chapter. Discussion on this specific topic will presented firstly with a broad overview of radio electronics and descriptions of main circuit functions. (See Figure 6-2 on page 99 and Figure 6-3 on page 99). The latter will describe common faults that occur within these circuit functions. This chapter covers analogue reception as this was available in the pre-2000 era of audio equipment. Commercial radio provided in most tuners is typically one of two bands: Amplitude Modulation (AM) or Frequency Modulation (FM). The essential difference between the AM and FM band is the carrier frequency and the way it is modulated. These two factors have an impact not on only on the quality of signal received, but also the potential interference and available reception to the tuner aerial.
6.1.2 • Radio reception The key to any clear, quality radio broadcast is to have a proper and maximised signal reception. The received signal will then pass through the RF amplifier stage and be extracted through various demodulation and other processes. These could include de-emphasis, beat removal (BFO). Radio reception via an aerial is the key to any radio tuner as it is the source signal where the content, music or speech will be extracted. A proper suited aerial with sufficient gain is paramount to effective performance of the tuner. AM stands for “Amplitude Modulation”, as AM radio signals vary their amplitude to adapt to the sound information that is being broadcast through the wavelengths. While changes in amplitude occur on FM radio as well, they are more noticeable in AM radio because they result in audible static. So, essentially, when you’re switching the channels on an AM radio, you’re hearing changes in amplitude, which is why distant broadcasts with weak signals will come across as very faint with the sound largely dominated by static. FM stands for “Frequency Modulation,” and, unlike AM radio, sound is transmitted through changes in frequency. While both FM and AM radio signals experience frequent changes in amplitude, they are far less noticeable on FM. During an FM broadcast, slight changes in amplitude go unnoticed because the audio signal is presented to the listener through changes in frequency, not amplitude. So, when you’re switching between stations, your FM antenna is alternating between different frequencies, and not amplitudes, which produces a much cleaner sound and allows for smoother transitions with little to no audible static Tips
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--
Lead wire connecting an external aerial to a tuner input is made of two specific types: 300Ω twin lead or 75Ω coaxial. Although coax cable provides better electrical noise from cars CB radios and building or road light fixtures, twin lead has lesser transmission loss. 1.4 dB per 100 feet (approx. 30.5 metres). However saying this if the twin lead is wet signal loss can be as high as 8dB per 100 feet. These figures compare to that of coaxial cable where the loss is typically of 3 DB per 100 feet.
--
Flat ribbon twin lead can be mechanically strengthened by twisting approximately every 4 feet (120 cm) to avoid movement from winds and
Chapter 6 • Servicing of Tuner /Home Entertainment Amplifiers reducing radio interference. Also when installing twin ribbon keep away from conducting material such as metal down pipes or wood that may become wet due to weather conditions such as rain. This will reduce signal strength and increase background noise levels. A standoff wire support is the best approach to installing ribbon cable to avoid these issues of loss signal.
6.2 • Analogue AM & FM Radio A functional block diagram of both an AM & FM radio is shown below.
RF Amplifier
Mixer
IF amps
Detector
To Preamplifier
Local oscillator
Figure 6-2 AM Radio block diagram
RF Amplifier
Mixer
IF amps
Radio detector
To Preamplifier after L-R decoding
Local oscillator
Figure 6-3 FM Radio block diagram
6.2.1 • Superheterodyne design AM and FM radio operation is based on superheterodyne design and its meaning is important here prior to describing the elements of these radio receivers. Heterodyning simply means to mix two frequencies together so as to produce a beat frequency, namely the difference between the two. The term superheterodyne refers to creating a beat frequency that is lower than the original signal. The advantages of this are: It caters for a relatively lower frequency range that components can operate in an optimal fashion. Higher frequencies are more complex in design due to other factors such as intrinsic capacitance and inductance. It allows many components to operate at a fixed frequency (IF section) and therefore they can be optimised. The fixed IF frequency can be easier designed than working over a wide range of frequencies. Overall, a more economical approach.
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Chapter 7 • Cassette Deck players
Chapter 7 • Cassette Deck players 7.1 • Introduction The audio cassette deck player was a common, popular source of music entertainment which was integral to early Hi-Fi systems. The Compact Disc (CD) and player (Refer to Chapter 9 on page 163) superseded the magnetic tape system as both a recording and playback medium. The very popular audio cassette during its time was a light-weight, quality medium (originally developed by Philips). At the time there were three types of magnetic recording systems commercially available: reel-to-reel, audio cassette and cartridge (used in automobiles). The first of these offered high quality recordings, however the audio cassette became the popular choice for Hi-Fi systems. For this reason the chapter's focus is on audio cassette and associated deck player. The principle of operation will be discussed and the associated common faults highlighted. This operation also extends to portable cassette players such as radio cassette players and Walkmans. Prior to discussing cassette player operation, its overall performance depends heavily on electronic circuits, tape heads and cassette tape itself. Note: Magnetic tape systems had better channel separation over vinyl disk recordings.
7.1.1 • The audio cassette Before describing the operation of tape decks, the description of the source of audio itself, the audio cassette is well worth reviewing to appreciate the functionality of the tape deck. Figure 7-1 on page 124 shows an audio cassette with its labelled components. Audio cassette tape can be adaptable to both mono (one channel) and stereo modes. A Stereo recording can be played on a mono deck cassette player. This is because the two stereo tracks are on the same surface area of the tape as the mono track. The playing (or record) times of tapes were 30, 60, 90 and 120 minutes. Note: Due to the long playing time of 120 minute length tapes, they are comparatively thin and more susceptible to breakage and stretching. Magnetic Tape surfaces There are three main types of oxide coatings commercially available: normal, chrome and metal. The types are based on the oxide coating of the tape and the performance offered in terms of frequency response and noise distortion. Normal tapes are ferric oxide coated, the best of these being the ‘UD’ type. ‘UD’ stands for Ultra Dynamic and tape manufacturer Maxwell had a series of these high quality tapes. The second type is the chromium oxide tape that offers even better performance, quality and output levels. They do however require a tape deck with appropriate bias and equalisation to allow the performance to be realised. The last of these is metal tape (ferric oxide) that offers better high frequency response. The audio cassette consists of two hubs or reels. The recorded tape is initially wound on one hub, prior to playback and is appropriately referred to as the supply hub. When the cassette is inserted into the player and the play function is activated, the take up reel draws the magnetic tape supply at a constant speed. During any high speed movement it draws the supply magnetic tape at a constant speed. During a high speed movement in both directions, forward and backward, this action is performed without the magnetic tape touching the head. The tape is steadily guided past the play head and driven by the capstan shaft (hence the capstan hole shown in Figure 7-2 on page 124 and the pinch
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Retro Audio: A Good Service Guide roller. The play heads could be described as electromagnets and the magnetic tape as
Figure 7-1 The audio compact cassette having multitudes of recorded imprinted magnetic particles. Further description of play heads is provided later in this chapter.
ERASE HEAD
REPLAY HEAD
RECORD HEAD
CAPSTAN
PINCH WHEEL
Figure 7-2 The audio compact cassette tape path The pressure pad applies gentle pressure on the magnetic tape to the tape head allowing good contact as it passes from the supply reel to the take up reel via the guide rollers. This pad is essential for high frequency response at slow cassette speeds. However, the pad must not be too tight to create tape damage. A magnetic shield is found in most good quality tape cassettes. In the earlier days of cassette technology, players and recorders utilised high impedance heads. Due to this, the head is susceptible to noises from stray electromagnetic fields. Changing technology allowed for modern heads to have lower impedances and being relatively immune to stray fields of the era. The shield is maintained in order to be compatible with older cassette machines. The shield material is made from non-magnetic material with good permeability to draw the stray magnetic fields away from the head. Slip sheets play an important role in wow and flutter levels of a moving tape. These sheets act as bearing surfaces for the hubs and as gentle guides for tape packs. They provide uniform tape travel and ultimately reduce tape edge damage.
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Chapter 8 • Repairing turntables
Chapter 8 • Repairing turntables The turntable (or record player) was a popular entertainment unit in many households until the early 80s. The technology of this device was able to continually improve over time with respect to the player's performance. Prior to vinyl records (and their memorable artful covers or sleeves) being eventually superceded by the digital formatted Compact Discs (CDs) of the day, the record player was hugely popular. The player has seen a recent resurgence, so much so, that new manufacturing of new record players has taken place for the first time in years. This popularity is part of a mass sentimental movement towards retro products of the past and justifies turntable repair as one of the chapters in this book. As with all relevant chapters in this book, an overview of Hi-Fi entertainment equipment will first include a description of working turntables then followed by their most common associated faults. Bearing in mind that the turntable is essentially a mechanical device, the chapter will provide more of a mechanical overview of the turntable. The common faults encountered will predominantly, be of a mechanical nature. An attempt will be made however to document electrical faults that the reader could be faced with. In the later part of the era of turntable design, more advanced electronics were used to overcome particular issues which led to lighter and more economical production designs. These designs took away the elements of instability that older and heavier devices had like their heavier platters and metal linkages to switch RPM speeds. This provided natural instability and impacted on performance, particularly Wow and Flutter where advanced electronic techniques then could now compensate for this. Like any type of commercially available audio equipment, there are performance limitations. These are of course dependent on the quality of unit. The range of possible turntable faults is generally limited to wear on parts such as rubber belts or friction driven tyres. Visual symptoms presented in the operation of the record player offer in most cases enough information to the issue in hand. Many issues only require adjustment of mechanical settings.
8.1 • Description of the turntable To begin discussing turntables, they can be divided distinctly into two areas of operation: the turntable drive and the tonearm with connecting cartridge and stylus. These two distinct systems are presented in Figure 8-1. The turntable drive’s function is the motor rotation of the vinyl record on a platter at a constant and stable speed. Turntable components Motor Friction Drive System Platter
Media & signal sensing components Vinyl record Stylus and cartridge Tone arm
Electrical Power and user control RPM selection Stop/Play Cueing
Figure 8-1 The two operational systems of a turntable with common power and user control
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Retro Audio: A Good Service Guide The tone arm with end cartridge contains a stylus (or needle) to convert the vibrating needle to an electrical signal. The vibration originates from the prerecorded groove inscription on the vinyl record. This groove is hundreds of metres long (on each record side) and moulded from a master disc when the record was produced. See Figure 8-2. A Sound wave from a pure unvarying frequency produce compressions and rarefication of air. This is how the same sound wave may look from being inscribed on the master disc for vinyl record reproduction.
Figure 8-2 Grooves on the surface of a vinyl disc under a microscope Over decades of development of the record player, four distinct design types evolved. These were: Manual Operation – the user switches on the revolving turntable with a loaded record, sets and removes the record tonearm at the respective start and end of play for. The user then switches off the turntable. Semi-automatic – the user switches on the turntable with the loaded record, sets the tonearm at the start of play of the record, but at the end of the record the tonearm lifts off and turntable switches off automatically. Fully Automatic – the user sets the tonearm at start of play of the record and the turntable starts automatically. The tonearm returns to the rest position at the end of play with a final switching off of the turntable. Variations of this mode are where the user starts the turntable and the tonearm loads automatically or where the record can play several times automatically. Record changer – multiple records are played in order of how they are loaded. After each record is played to the end, the tone arm returns to the rest position and the next record in sequence drops down to the platter. The tonearm then automatically loads and plays to the end of the record play and again automatically returns to the rest position. This sequence of actions repeats until all loaded records have been played where the tone arm finally unloads and turntable switches off.
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Chapter 9 • Repairing CD players (CDPs)
Chapter 9 • Repairing CD players (CDPs) With the progress in digital electronic technology in the 1980's, the CD player fast entered into the home consumer entertainment market. It quickly superseded its analogue counterparts such as the compact audio cassette and vinyl record. The fast growing popularity of digital formats was not coincidental and understanding of the digital principles of CD and PCM go some way to explaining this. With so much literature and theory already available for CD players, this chapter will be focused on the main servicing issues encountered with CD players. Attention will be given to the most likely issues that occur with CD players of the era and only those where repair is warranted (within the limitations of the test equipment and tools in hand). Many faults, particularly of those pertaining to optical functions do not warrant repair. Combine this limitation with the very high scale integration designs and manufacturing techniques of surface mounted devices (SMDs), this chapter will at least offer an approach to repair on a basic level. It will provide information that the author sees more valuable to the reader in order to allow for basic fixes. This has not been the case for the last three Chapters (6, 7 and 8) where repairs are more achievable due to less integration. Noting Chapter 7 on Cassette deck players and Chapter 8 on turntables, a respective capstan or turntable motor were the only servo type controlled utilised. CD players require several servo systems dedicated to their multiple functions.
9.1 • The CD player – A general operational description As with the discussion format of the two previous chapters, a good starting point to discussion of the CD player is to first look at the media it plays i.e. the Compact disc or CD. The CD player of the time catered for two sized CDs: 8 cm and 12 cm. The playing time of the 8cm disc was only 20 minutes compared to the maximum playing time of 74 minutes for its 12cm counterpart. Table 9-1 provides general information on the physical specifications of the more popular 12cm disc. Table 9-1 Physical specifications of 12 cm Compact Disc Parameter description
Specification
Additional note
Disc material
Glass /photo resist coating
Manufactured through highly precision processes
Disc Diameter
120mm
Disc thickness
1.2mm
Centre hole diameter
15mm
Recording diameter limits
46 to 117mm
Signal (playback) diameter limits
50 to 116 mm
Rotation
Anticlockwise in reference to laser
Laser normally on underside of CD
Lineal scanning speed
1.2 m/sec to 1.4 m/sec
To maintain constant data bit rate slower rotational speed as scanning towards outer diameter of CD i.e. slowing to 1.12 m/s
Playing time
Maximum 74 minutes
Nominally 60 minutes
As indicated in the Table 9-1, the CD plays from the centre and gradually moves outward. Due to the Optical Pick-up Unit (OPU) outward movement, it slows down to
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Retro Audio: A Good Service Guide maintain a constant data rate from the unit. The digital data on the CD is in a binary format consisting of 1s and 0s. This information is found in the form of detected ‘pits’, ‘bumps‘ and the CD surface (termed ’land’.) See Appendix D on page 191 on the explanation of CD data for further detail. This information contains much packed data and is advantageous for optimising and limiting playback errors.
9.1.1 • Reading the CD The Optical Pick-up Unit (OPU) contains a 5mW solid state laser diode. The beam from the diode travels through a series of lens and a beam splitter controlled by focusing mechanics. Spindle table
Chrome plated guide rails
Laser pickup lens Laser pickup
Screw drive to move entire laser pickup
Sled drive motor
Figure 9-1 Optical Pick-up Unit (OPU) In general, the beam through system control processes focuses on the reflective pits/ bumps and lands on the CD. Variation of light intensity from the CD's reflective surface is then passed to a photo detector via detector lenses. Most CD systems from the era contained four individual servo systems: Focus, Tracking, Carriage and Radial Servo. The last of these (Radial) is the actual optical assembly itself. The functions of this assembly contain both tracking and carriage servo systems. Because of this, only three systems are represented in the workings of the CD player. A very general description of each these three systems are given in the following sections.
9.1.2 • Focus servo The purpose of this servo is to ensure the laser beam is in ’focus‘ mode on the CD playing surface. This is achieved through the focus amplifier where the focus error is amplified and the error signal supplied to the focus coil. The coil is mounted to the objective lens as part of the optical assembly to allow for correcting vertical movement. This movement maintains focus of the laser on the playing surface of the CD.
9.1.3 • Tracking servo A very similar operation occurs with the tracking servo, however it amplifies any tracking error signals. That is, it enables the laser beam to accurately track across the CD playing surface. This error signal is passed to a tracking coil. The coil too is part of the objective lens of the optical assembly allowing for lateral or sideways correcting movement.
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Chapter 10 • Speaker & Microphone Repairs
Chapter 10 • Speaker & Microphone Repairs 10.1 • Speakers Speakers being the audible output of a sound system are of vital importance in the overall sound quality of a system. They are the last stage of the sound system and therefore sound can be only as good as what the speakers deliver to the listener. On this point, the human ear is in most cases the best test ‘tool‘ one can use to detect any sound abnormalities. Discussion in this chapter will be limited to the moving coil speaker driver, the most popular format of the era of discussion in this text. This typical speaker system of the time was used in alliance with the sound system components discussed in earlier chapters. Poor or serious performance issues may be due to many factors other than damaged speaker drivers. Due to sound being dispersed as sound waves from the speaker drivers, the physical environment of the driver sound wave requires to be correctly set up. This assumes the electrical signal supplied to the driver itself is within nominal specifications. Also the speaker box and internal components are correctly designed for the driver. More specifically, the speaker box is required to be sealed using damping sound absorbing material such as fibreglass. Sealing of the enclosure prevents low frequency waves from emanating outside the enclosure causing wave cancellations. These sound cancellations are around 700 Hz and above. The grill requires a loose woven fabric so as to not impede high frequency sound from the tweeters. Considerations such as impedance matching from the amplifier to speakers or the correct wiring to the speaker terminals all impact upon the optimal performance of a speaker system. To appreciate these, description of the determining factors of the sound system will follow, starting with speaker drivers.
10.1.1 • The speaker enclosures or boxes The speaker or termed driver is at the heart of any speaker system. Speaker drivers are of various sizes. The size of a speaker is related to the frequency that it transmits. The larger the speaker, the lower the frequency. Three categories of speakers in order of size (largest to smallest) are used in speaker enclosures: termed woofers, mid‑range and tweeters. Woofers (bass speakers) are used for 20-2,000Hz (2KHz) range, the midrange 500 to 8,000Hz (8KHz) and 4,000 (4KHz) to 20,000Hz (20KHz) for tweeters. These drivers are usually wired within the enclosure containing internal crossover networks. The purpose of these networks is to filter and distribute the incoming electrical signal from the amplifier to three frequency ranges to the respective drivers. They are low, mid and high frequency to the respective woofer, mid-range and tweeter drivers. The crossover networks typically consist of passive components constructed from capacitors or inductive coils.
10.1.2 • Moving Coil Speaker Driver The function of a speaker is to convert electrical energy into sound energy. This conversion is performed through speaker coil movement. Figure 10-1 on page 174 shows alternating current in both directions of the speaker coil. The frequency or the signal replicates the speed of the moving coil as it moves in and out with each change of polarity. A high frequency would show a high rate of fluctuation. The volume or sound intensity is represented by how far the coil extends in and out of the cone. Both frequency and volume are replicated as part the cone movement. The cone moves the surrounding
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Retro Audio: A Good Service Guide air, producing a corresponding sound reverberation and compression according to the signal received by its source. In most cases this would be a sourcing amplifier.
Figure 10-1 Diagram of a moving coil speaker driver With reference to the physical structure of the moving coil speaker driver, it is constructed with five main components. They are: •
Frame
•
Magnet
•
Voice Coil
•
Suspension system
•
Cone
Each of these will briefly described Surround Diaphragm or cone
Voice coil former Dust cap
Frame or basket
Spider Top Plate Magnet
Pole piece
Voice coil
Figure 10-2 Basic components of a moving coil speaker driver The frame The frame (otherwise known as the “basket”) is used to hold all the driver components as a whole. The frame is also used to mount the driver in the speaker enclosure. Frames may completely cover smaller drivers to prevent larger woofer air pressures within the
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Appendix A • Common audio connectors and pinouts
Appendix A • Common audio connectors and pinouts
In Figure A-1 below is the common audio visual connectors found on most audio visual equipment and their respective pinouts.
2 pin DIN speaker connection
L R
3 1 524
3 pin DIN
L R
5 pin DIN 180°
7
L R
3
4 pin DIN
3
3 1 5
2
4
5 pin DIN 240°
5
2
4 pin DIN with plastic locator spigot
5
1 4
5 pin DIN 360° or domino
4
6 3
1 2
6 pin DIN
6
52 4
1
7 pin DIN
L R XLR + outline of plug design 1 3 5 7 9 11 13 15 17 19 21
FM aerial plug AM aerial plug In both cases the centre ‘pin’ is a plastic locator
2 4 6 8 10 12 14 16 18 20 SCART Left channel
Headphone plug
Right channel Common
Pin
Use
Level
Pin
Use
Level
1 2
Audio out (R) Audio in (R)
0.5 V rms 0.5 V rms
12 13
No connection Red ground
-
3
Audio out (L)
0.5 V rms
14
Data/status switch ground
-
4 5 6
Audio ground Blue ground Audio in (L)
0.5 V rms
15 16 17
Red in (RGB) RGB blanking switch signal Video ground
-
7
Blue in (RGB)
-
18
Blanking ground
-
8 9 10
Data/switch signal Green ground No connection
-
19 20 21
Video output (CVBS) Video input(CVBS) Screen plate surround
1.0 V p-p 75Ω 1.0 V p-p 75Ω -
11
Green in (RGB)
-
Figure A-1 Common audio connectors and pinouts
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Appendix B • Additional Information
Appendix B • Additional Information B.1 • Resistor colour code chart In Figure B-1 shows the colour codes, tolerances and temperature co-efficient data for the three most common types of resistors.
Figure B-1 Resistor colour code and tolerances
B.2 • Capacitor colour code chart In Figure B-2 shows the colour codes, tolerances and temperature co-efficient data for the three most common types of resistors.
Figure B-2 Capacitor colour codes
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Index
Index
Braking system 130
C
A AC - sensitivity 30 Active Component testing 35 Active to Earth 71 AC Voltage 30 AM Detection 101 Amplifier faults FET output stages 112 IC output stages 112 No output 112 Signal Path issues 113 Transistor 112 Analogue AM 99 Antenna problems 102 Antistatic 87 audio cassette 143 Audio circuits 142 audio connectors 181 Audio drivers 49 Automatic Gain Control 106 Auto stop detection Electronic detection 132 Mechanical detection 132
B Basic checks 118 Bass response losses 116 Battery Power 83 Belt Drive 152 Belt replacements 146 belts 157 Belts, cogs pulleys 49 Bench Power supplies 33 Bent Capstan 140 Board Damage 88 Board Plugs 87 braking 128
Cables 116 Calibration 32 capacitance 77 Capacitor code chart 183 Capacitors 43, 59, 77 capstan 129, 140 Carriage servo 166 Cartridge 154 cartridge faults 159 CD players 163 ceramic cartridge 155 Checking Fuses 118 Checking wear 144 Circlip pliers 37 Circuit tracing 58 Cleaning 144 Clipping distortion 114 Compact Disc 169 condenser microphone 177 cone 174, 175 connectors 116 Control linkage 128, 129 Crossover distortion 114
D Darlington Pair 48 DC Current 30, 32 DC motors 126 DC Motor windings 71 DC - sensitivity 30 DC Voltage 30, 31 Deck Motors 125 Decoder 166 Decoding circuitry 166 Demodulator 101 Desoldering 52, 89 Detector faults
â—? 193
RETRO AUDIO Paul Hetrelezis
ISBN 978-1-907920-58-5
www.elektor.com
This ‘hands-on’ servicing guide opens with fundamental considerations of the work space of repair and servicing. This includes a comprehensive discussion of essential test equipment and tools. Two chapters are devoted to obtaining servicing information about repair and obtaining spare parts. A key chapter is on general diagnosis and testing and includes the discussion of resistance, capacitance and inductance. These electrical properties are regularly in the mind of the repairer, so understanding of them is a key objective of this book. The next chapter is about time saving repair techniques and ensuring quality repair. The remaining chapters discuss entertainment equipment itself. Each of the chapters begins with an orderly discussion of the theory of operation and common and not so common problems specific to the equipment. All chapters conclude with a summary.
LEARN DESIGN
Elektor International Media BV
Today there is a re-emerging, nostalgic interest in vinyl records and associated music entertainment gear. With this interest, there is a paralleled market for the repair of this gear.
A GOOD SERVICE GUIDE
RETRO AUDIO
● PAUL HETRELEZIS
My passion for electronics commenced in the early 1970s. After many ventures in electronics as a teenager, such as building projects from electronics magazines, my formal education in this area began in the early 1980s through to completing a BEng in Electronics in 2001. This was supplemented by spending all my spare hours contently in my workshop repairing brown goods.
The intention of the book is to offer the reader understandings, ideas and solutions from the perspective of a workbench technician and electronics hobbyist. It is a descriptive text with many tables of useful data, servicing tips and supplementary notes of not so common knowledge.
RETRO AUDIO – A GOOD SERVICE GUIDE
A GOOD SERVICE GUIDE
Paul Hetrelezis LEARN DESIGN SHARE
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