PRACTICAL ELECTRONICS TROUBLESHOOTING Second Edition James Perozzo

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DELMAR PUBLISHERS INC.®

Contents Preface/xiii

chapter one Some Necessary Basics

Chapter Overview/1 Necessary Background/1 A Few Definitions/6 The Test Bench/11 Summary/12 Review Questions/13

chapter two Kinds of Electronics Problems

Chapter Overview/14 Complete Failures/14 Poor Performance/14 Tampered Equipment/15 lntermittents/15 Motorboating/19 Massive Traumas/19 Transients/22 Overheated Part Failures/23 Hum Problems/25 Distortion Problems/26 Multiple Problems/27 Microphonics/28 Noisy Controls/28 Operator-Induced Problems/28 The Tough Problems/29 Summary/29 Review Questions/30

chapter three System Troubleshooting

Chapter Overview/31 Investigate the Report/31 Finding the Bad Unit/32 Wire-Bundle and Coax-Cable Problems/34

vi Contents

Signal Levels as System Operation lndicators/36 Replacement of Suspected Units of the System/38 Verify Proper System Operation After the

Replacement/39 Summary/39 Review Questions/40

chapter four Passive Components in DC and Low-Frequency Circuits

Chapter Overview/41 Passive Components in DC Circuits/41 Passive Components in 60 Hz and Audio

Sine-Wave Circuits/49 Passive Components in Pulse and Square-Wave

Circuits/58 Summary/68 Review Questions/69

chapter five Live-Circuit Testing

Chapter Overview/70 Safety and Cautionary Notes/70 Use of Circuit Card Extenders/71 Using the Schematic Diagram/72 If No Schematic Is Available/75 Summary/78 Review Questions/79

chapter six DC Troubleshooting

Chapter Overview/81 General Voltage Troubleshooting/81 Using Voltages to Find Analog Problems/91 A Most Important Concept/94 Opening the Equipment/96 Timely Shortcuts/97 Summary/97 Review Questions/97

chapter seven Fixing the Power Supply

Chapter Overview/99 Finding the Open Fuse/99 Analyzing Fuse Failures/99

Contents vii

The Power-Supply Block Diagram/101 Applying Input Power to the Power Supply/103 Troubleshooting an Overloaded (Shorted) Power

Supply/107 Troubleshooting an Inoperative Power Supply

(Good Fuse, No Output Voltage)/108 Troubleshooting the Voltage Regulator/110 Finding a Short in the Load on a Power Supply/116 Determine the Method to Locate the Short/117 Batteries as a Power Source/121 Summary/123 Review Questions/124

chapter eight How to Trace Analog Signals

Chapter Overview/125 Troubleshooting Digital Circuits/125 Troubleshooting Analog Equipment/125 The Block Diagram—Finding the Bad Area/126 Using a Bench Power Supply/127 Narrowing the Problem to an Area/131 Narrowing the Problem to a Stage/132 Signal-Tracing Considerations/132 Tracing the Unwanted Signal/134 Summary/134 Review Questions/135

chapter nine Audio and Low-Frequency Troubleshooting

Chapter Overview/136 Obtain All Reference Material Possible/136 Generic Low-Frequency Troubleshooting

Instruments/137 Output Devices and Instruments/138 Basic Low-Frequency Amplifier Circuits/143 Audio Distortion Problems/146 Troubleshooting Audio-Amplifier Consumer

Chips/150 Summary/150 Review Questions/151

chapter ten Special Techniques for Discrete Semiconductors in Operation

Chapter Overview/152

Troubleshooting the PN Junction Diode in Operation/152

Troubleshooting the Zener Diode Circuit in Operation/154

Troubleshooting the Bipolar Transistor Circuit in Operation/154

Transistor and Resistor Arrays/161 Troubleshooting FET Circuits/162 Troubleshooting UJT Oscillators/165 Troubleshooting Thyristors (SCRs)/166 Summary/166 Review Questions/167

chapter eleven Troubleshooting in Live Analog IC Circuits

Chapter Overview/168 Operational Amplifiers/168 Voltage Regulator ICs/174 Consumer IC Chips/175 Analog Switches/1 77 Optical Isolators/1 78 Summary/180 Review Questions/180

chapter twelve Radio Frequency Components and Troubleshooting

Chapter Overview/181 When a Problem Is Reported/181 Some Uniquely RF Components/182 A Review of Common Instruments Used With RF

Frequencies/183 Special Tools for RF Use/198 Working With Microvolt Signals in Receivers/199 Working With RF Watts and Transmitters/219 Making Transmitter Tests/221 Optional Transmitter Tests/225 Generic Adjustment of a Radio Transmitter/228 Summary/230 Review Questions/231

chapter thirteen Troubleshooting and Signal Tracing in Pulse Circuits

Chapter Overview/233 Terms Unique to Pulsed Waveforms/233

Contents ix

Source Instruments/235 Load Instruments/236 The Originating Pulse Circuit/241 The Processing Pulse Circuit/241 Pulse Uses/242 Summary/245 Review Questions/246

chapter fourteen Digital Troubleshooting Techniques

Chapter Overview/247 First Checks/247 Digital IC References Are Absolutely Necessary/248 Digital Troubleshooting Basics/248 The Digital Schematic Diagram/252 Basic Digital Gates/253 Instruments for Digital Circuit Troubleshooting/256 Tracing Signals Through Digital Circuits/269 Summary/276 Review Questions/276

chapter fifteen Troubleshooting Computer Circuitry

Chapter Overview/278 Additional Knowledge Required/278 Types of Computer Problems/279 Hardware Problems/279 Let the Computer Test Itself/280 Additional Checks to Make/281 Software Problems/282 Options and Hardware Setup Problems/283 Summary/283 Review Questions/284

chapter sixteen Dead-Circuit Testing

Chapter Overview/285 Don't Ruin Your Ohmmeter!/285 Using the VOM on the Resistance Function/286 Using the DMM on the Resistance Function/287 Using a Solid-State Tester/287 Making the Checks/289 Testing Component Resistance ln-Circuit/290 Summary/294 Review Questions/294

chapter seventeen Replacing the Part and Analyzing the Failure

Chapter Overview/296 Some Mechanical Tips and Considerations/296 Point-to-Point Wiring Repairs (Not Printed

Circuits)/298 Printed-Circuit-Board Repairs/298 Soldering on Printed Circuit Boards/299 Where to Get Parts/300 Replacing Parts/300 Cleaning and Repairing Damaged Boards/302 Checking the Bad Component/302 Final Precautions/322 Summary/322 Review Questions/322

chapter eighteen Alignment, Final Inspection, and Return to Service

Chapter Overview/324 Aligning Equipment/324 Reassembling the Equipment/329 Final Tests/330 The Paperwork/330 Packing for Shipment/331 Summary/332 Review Questions/332

chapter nineteen Routine and Preventive Maintenance

Chapter Overview/333 Why Mess With lt?/333 Using the Solid-State Tester to Predict Failures/334 TDR for Cable Maintenance and

Troubleshooting/334 Mechanical Maintenance/336 Solvents for Cleaning/336 Weathered Electronics/337 Summary/339 Review Questions/339

chapter twenty Techniques for Live Vacuum-Tube Circuits

Chapter Overview/340 Special Tools/340 Safety Notes/340

Contents xi

Chassis Wiring Color Code/341 Typical Vacuum-Tube Voltages/343 Troubleshooting Vacuum-Tube Circuits/348 The Cathode-Ray Tube/351 Summary/353 Review Questions/353

chapter twenty-one Basic Troubleshooting of Power-Line Circuits and Motors

Chapter Overview/355 Single Phase Power Distribution and

Troubleshooting/355 Three-Phase Power Systems/356 A Special Circuit/357 DC Motor Basics/357 The Alternator/360 AC Motor Basics/361 Troubleshooting Motor Circuits/363 Using the Oscilloscope on AC Line Problems/364 Summary/364 Review Questions/365

chapter twenty-two If the Right Part Isn't Available

Chapter Overview/366 Parts Substitutions/366 Summary/374 Review Questions/374

appendix I Resistor Color Codes

Two-Significant-Figure Color Code/376 Three-Significant-Figure Color Code/377

appendix II Electronics Schematic Symbols

Common Electronics Symbols/378 Semiconductor Symbols/380 Digital Symbols/382 Logic Symbols/383 Common Vacuum-Tube Symbols/384

appendix III Contributing Manufacturers of Test Equipment and Supplies/385

Index/387