How to TestAlmost Everything

Electronic3rd Edition

Oe/ton T. Horn

TAB BooksDivision of McGraw-Hill

New York San Francisco Washington, D.C. Auckland BogotäCaracas Lisbon London Madrid MeKico City Milan

Montreal New Delhi San Juan SingaporeSydney Tokyo Toronto

ContentsIntroduction

1 Test equipmentMultimeters 3Adapters for multimeters 9Oscilloscopes 10Signal generators 21Signal tracers 25Capacitance meters 25Frequency counters 27Servicing test equipment 28

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2 De voltage tests and power supplies 31Dc voltage measurements 31Problems with circuit breakers 32Checking for a hot chassis 33All-polarity voltmeters 34Polarity indicators 36Full-wave power supplies 39Measuring ac voltages 40Power supply ripple 41Shortened power transformers 43Power supplies with voltage dividers 44Power supplies with dropping resistors 45Power-supply circuits with branches 47Transformerless power supplies 49Half-wave voltage doublers 50Full-wave voltage doublers 51Full-wave bridge rectifiers 53

Electrolytic capacitors in series for higher working voltage 55Ac power supplies for transistorized equipment 56Power supplies from a transformer winding on a

phono motor 58Transistorized capacitance multipliers 59Checking capacitance multiplier circuits 60Transistorized series voltage regulators 62Transistorized shunt voltage regulators 63Three-transistor voltage regulators for transistor TV sets 64Transistorized dc-to-dc converters 66Testing dc-to-dc converters 68JC voltage regulators 68Reading battery voltages correctly 70

3 Current testsPower measurements 74Measuring the dc drain of an auto radio 75Dc current measurements in transistor portable radios 76Testing power transformers for internal shorts 78Substitute power testers 79Finding overloads in power supplies 81Selecting the bias of a power transistor with a

current meter 82Measuring large currents 83

4 VOM and VTVM testsMeasuring contact resistance with a VOM 87Measuring voltage drop in long battery wires 88Jdentifying uncoded wires in multiconductor cables 90Testing capacitor leakage with a VTVM 91Measuring very high resistances 93Checking diodes by the balance method 94Checking video-detector diodes with an ohmmeter 95Checking video-detector diodes in-circuit with

an ohmmeter 96Checking transistors with a VOM 98Voltage and resistance tests 99Stacked stages 104Bad base bias 106Dealing with noise pick-up 107

5 Oscilloscope testsCalibration for direct measurements 113Oscilloscope probes 114Triggered and gated sweep 117

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Measuring dc voltages with an oscilloscope 119Measuring ac voltages with an oscilloscope 121Measuring frequency with an oscilloscope 125Analyzing distortion with an oscilloscope 127Square-wave testing 133Time and phase measurements 136Using a sweep-frequency signal generator 139Lissajous figures 140Reactance and impedance measurements 151Testing for filter ripple with the scope 155Checking ca transmitter modulation with the scope 157

6 Component testsDetecting thermal drift in resistors 159Checking and repairing potentiometers 160Capacitance testing 164Testing variable capacitors 167Testing inductors 168Measuring inductance 173Shorted power transformers 174Testing integrated circuits, modules, and PC units 183A quick check for microphones 184Checking phone cartridges with the scope 185Impedance checker for speakers 186Testing diodes 189Replacing transistors 191Derating components 191

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7 TV tests 193Measuring very high voltages 195Measuring focus voltages in color TV 197Checking color picture tubes with a VOM 199Extension cables for testing TV tuners 201A quick tuner gain check 202Checking for operation of the 3.58 MHz color oscillator 203Testing for presence of high voltage, horizontal

sweep, etc. 204Checking for high voltage with a neon tester 205Setting a horizontal oscillator on frequency by

comparing with video 206Testing frequency in vertical-oscillator circuHs 206Finding the cause of sync clipping with the scope 209Finding sync troubles with the scope 211TV signal tracing and gain checks with an RF or AF

signal generator 215

Signal tracing with the scope and color-bar patterns 219Using the scope to set the duty cycle of the horizontal

output transistor 221How not to read voltages: The "do not measure"

points in TV 222Blown audio output transistors 223Dealing with dead sets 223

8 Special testsMeasuring peak voltages without a voltmeter 226Using a pilot lamp for current testing 227A voltage divider far obtaining very small audio signalsA quick test for audio power output 229Measuring amplifier output power with a multimeterTesting an audio amplifier's frequency response 233A quick test for the RF power output of a transmitterMeasuring base bias voltage in high-resistance circuitsFinding breaks in multi-conductor cables 239Finding a break in a coaxial cable with a capacitance

tester 240Measuring true rms voltages 241Testing transistors 243Testing Zener diodes 250Testing FETS 253Testing SCRs 256Testing ICs 260

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9 Signal tracing and alignment tests 263Checking the calibration of an RF signal generator 263Setting an RF signal generator on a crystal frequency 265Finding the exact point of a zero beat 266Test records: Good substitutes for the audio-signal

generator 267Using radio signals for testing stereo or PA systems 268Using a communications receiver as an RF signal

locator or tracer 269The ac voltmeter for gain checks and signal tracing 271Power output tests for PA and hi-fi amplifiers 272

10 Digital circuitsLogic probes 280Monitoring brief digital signals 281Signal tracing in a digital circuit 282Digital signal shape 282Power-supply problems in digital circuits 282

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Logic analyzers 283Pulse generators 283Flip-flops 284Tri-state logic 294Sequencing problems 295Noise and glitches 298

11 Flowcharting and troubleshooting 301Basic flowchart 302Servicing without a schematic 305Systems comprised of multiple pieces of interconnected

equipment 308

Index