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10-1 Electronics Principles & Applications Eighth Edition Charles A. Schuler Chapter 10 Troubleshooting (student version) ©2013 McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. 10-2 INTRODUCTION • Preliminary Checks • No Output • Reduced Output • Intermittents • Operational Amplifiers • Automated Testing McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. 10-3 Dear Student: This presentation is arranged in segments. Each segment is preceded by a Concept Preview slide and is followed by a Concept Review slide. When you reach a Concept Review slide, you can return to the beginning of that segment by clicking on the Repeat Segment button. This will allow you to view that segment again, if you want to. McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. 10-4 Concept Preview • Observation, analysis and limiting the possibilities are the key elements of troubleshooting. • The troubleshooting process should begin with a system point of view. • Software problems can produce symptoms that act like hardware failures. • Component level troubleshooting is based on circuit laws. • Electrostatic discharge can damage or destroy solid state components. McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. 10-5 GOAL • Good troubleshooting • Observe the symptoms • Analyze the possible causes • Limit the possibilities McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. A System Point of View 10-6 Diagnostics * adjust framostat * synthesizer off * buy low * sell high Other hardware Symptoms? Causes? Components Power? Software Network Controls Connectors McGraw-Hill Inputs © 2013 The McGraw-Hill Companies, Inc. All rights reserved. 10-7 Don’t forget to check for blown fuses! McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. 10-8 SYMPTOMS FAULTS VIN = 0 VLOAD = 0 VIN < NORMAL VLOAD < NORMAL R1 OPEN VLOAD > NORMAL R1 > NORMAL VLOAD SHOWS NOISE C OPEN C SHORTED VIN ZENER OPEN R1 RLOAD C ZENER SHORTED ILOAD > NORMAL McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. 10-9 Electrostatic Discharge (ESD) McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. 10-10 ESD PREVENTION • device packaging • minimize device handling • minimize motion • use a wrist strap • stand on ESD work mat • use ESD work surface • touch ground first • ionized air • instrument grounding • follow procedures McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. 10-11 G.O.A.L. quiz The key words in troubleshooting are observe, analyze and ________. limit Symptoms must be analyzed from the __________ point of view. system With computer based systems, a fault can be caused by hardware or _________. software Some solid-state devices are easily damaged by ____________ discharge. electrostatic Technicians sometimes wear a wrist strap to prevent _________. ESD McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. 10-12 Concept Review • Observation, analysis and limiting the possibilities are the key elements of troubleshooting. • The troubleshooting process should begin with a system point of view. • Software problems can produce symptoms that act like hardware failures. • Component level troubleshooting is based on circuit laws. • Electrostatic discharge can damage or destroy solid state components. Repeat Segment McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. 10-13 Concept Preview • Analysis by signal injection starts at the beginning of the signal chain. • Analysis by signal tracing starts at the end of the signal chain. • Signal generators and oscilloscopes are commonly used for both of the above methods. • In-circuit testing with an ohmmeter can be misleading due to multiple paths. • Signal comparison is handy when a working channel or circuit is available. McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. 10-14 SIGNAL INJECTION METHOD STAGE 1 STAGE 2 STAGE 3 STAGE 4 SIGNAL GENERATOR McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. 10-15 SIGNAL INJECTION METHOD (another approach) STAGE 1 STAGE 2 Some technicians prefer the “divide and conquer” approach as it often saves time. STAGE 3 STAGE 4 Start in the middle. SIGNAL GENERATOR McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. 10-16 SIGNAL TRACING METHOD (Divide and conquer works here too.) STAGE 1 McGraw-Hill STAGE 2 STAGE 3 STAGE 4 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. 10-17 Additional paths cause the reading to be low. C V B mA E R1 In-circuit ohmmeter testing can be misleading. McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. SIGNAL COMPARISON METHOD (Divide and conquer works here too.) LEFT STAGE 1 LEFT STAGE 2 LEFT STAGE 3 LEFT STAGE 4 RIGHT STAGE 1 RIGHT STAGE 2 RIGHT STAGE 3 RIGHT STAGE 4 McGraw-Hill 10-18 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. 10-19 Concept Review • Analysis by signal injection starts at the beginning of the signal chain. • Analysis by signal tracing starts at the end of the signal chain. • Signal generators and oscilloscopes are commonly used for both of the above methods. • In-circuit testing with an ohmmeter can be misleading due to multiple paths. • Signal comparison is handy when a working channel or circuit is available. Repeat Segment McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. 10-20 Concept Preview • Open capacitors do not usually cause dc voltage errors. • An open emitter bypass capacitor will cause the voltage gain to be abnormally low. • An open coupling capacitor will break the signal chain. • Shorted capacitors usually do cause dc voltage errors. • Open resistors usually do cause dc voltage errors. • An open resistor can cause an amplifier to operate in saturation or cutoff. McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. Open might cause hum or noise 10-21 If any of these are open, there are no dc voltage errors. Open causes decrease in gain Open causes loss of signal McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. Short causes amplifier voltages to be zero 10-22 If any of these are shorted, there are dc errors. Short causes increase in transistor current McGraw-Hill Short causes loss of B-E bias and transistor is cutoff (depends on prior stage) © 2013 The McGraw-Hill Companies, Inc. All rights reserved. 10-23 This instrument will find several kinds of faults. For capacitors, it can determine shorts, opens, and high series resistance (which can cause bypass capacitors to not do their job). McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. 10-24 If this is open, the amplifier voltages are 0. McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. 10-25 If either of these is open, the transistor is in cutoff. Which of these two faults will produce a non-zero emitter voltage? McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. 10-26 If this is open, the transistor approaches saturation. Will the collector voltage be high or low? McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. 10-27 If this is open, the transistor collector goes to zero volts. Will the base voltage be off very far? McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. 10-28 Component level troubleshooting quiz Ohmmeter troubleshooting can be misleading when performed _____ a circuit. in Dc voltage errors are usually not caused by _________ coupling capacitors. open A shorted coupling capacitor could cause the Q-point to move to cutoff or ______. saturation When a base bias resistor opens, the Q-point __________ changes. always Stage-by-stage verification with an oscilloscope is called signal ____________. tracing McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. 10-29 Concept Review • Open capacitors do not usually cause dc voltage errors. • An open emitter bypass capacitor will cause the voltage gain to be abnormally low. • An open coupling capacitor will break the signal chain. • Shorted capacitors usually do cause dc voltage errors. • Open resistors usually do cause dc voltage errors. • An open resistor can cause an amplifier to operate in saturation or cutoff. Repeat Segment McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. 10-30 Concept Preview • A dummy load should be used when verifying power output. • Triangle waves make it easy to recognize signal distortion. • Intermittents might appear with changes in supply voltage, with temperature, or with vibration. • When an op amp output goes to its maximum negative or positive value it is “at the rail.” • When an op amp is at the rail, there could be an open resistor, a resistor out of tolerance, or a bad supply voltage. McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. 10-31 VERIFYING POWER OUTPUT AMPLIFIER DUMMY LOAD SIGNAL GENERATOR McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. 10-32 CHECKING FOR DISTORTION AMPLIFIER Crossover TRIANGLE GENERATOR McGraw-Hill Clipping © 2013 The McGraw-Hill Companies, Inc. All rights reserved. 10-33 Making intermittents show up • • • • • • • McGraw-Hill System view (Is any software involved?) Wiggle it Thump it (don’t get carried away) Heat it (don’t melt anything) Cool it Raise supply voltage (moderate amount) Lower supply voltage © 2013 The McGraw-Hill Companies, Inc. All rights reserved. 10-34 Suppose a signal source has a dc component that must be eliminated but a coupling capacitor is not acceptable. Here’s a solution: add a negative voltage to cancel the positive dc offset of the source. 5 kW -5V 1 kW 100 kW 1 VDC RL 1 kW McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. 10-35 Suppose the output voltage is at negative saturation. Could the 5 kW resistor be open? Could the - 5 V supply be at fault? -5V 5 kW 1 kW 100 kW - 12 V 1 VDC RL 1 kW What else could be wrong? McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. 10-36 Verification and intermittent quiz Amplifier power output is best measured using a ________ load. dummy The waveform that makes it easy to see amplifier distortion is the _______. triangle Intermittents caused by poor connections may be located by using __________. vibration Some intermittents can be made to appear by changing temperature or supply _____. voltage When an op amp shows dc output error, check first for dc _________ error. input McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. 10-37 Concept Review • A dummy load should be used when verifying power output. • Triangle waves make it easy to recognize signal distortion. • Intermittents might appear with changes in supply voltage, with temperature, or with vibration. • When an op amp output goes to its maximum negative or positive value it is “at the rail.” • When an op amp is at the rail, there could be an open resistor, a resistor out of tolerance, or a bad supply voltage. Repeat Segment McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. 10-38 Concept Preview • Boundary scan was developed to replace the bed of nails manufacturing test procedure. • Boundary scan can also be used for field service work. • Scan cells support both normal operation and diagnostic modes which can verify inputs and outputs, test circuit board traces, and check device functions. • Boundary scan devices have at least four extra pins: test data in, test data out, test mode select, and clock. McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. Boundary scan functions 10-39 During a scan, devices can be checked for proper function. During a scan, I/O ports can be checked for proper function. During a scan, circuit traces can be checked for proper function. Virtual nails Scan chain Test data in Test data out McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. 10-40 More boundary scan functions McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. 10-41 Each boundary scan chip pin is connected to cell. Normal input (from core) Serial output Cell Normal output Core Serial input Scan chain McGraw-Hill When The The thenormal serial normal output output inputcan is can routed be be to the normal driven by output, the serial the chip input. works as if there was no scan function. © 2013 The McGraw-Hill Companies, Inc. All rights reserved. Boundary scan version Test data out Test mode select McGraw-Hill SN74BCT8244A Octal buffer/driver SN74BCT244 10-42 Test data in Test clock © 2013 The McGraw-Hill Companies, Inc. All rights reserved. 10-43 Analog boundary scan McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. 10-44 Concept Review • Boundary scan was developed to replace the bed of nails manufacturing test procedure. • Boundary scan can also be used for field service work. • Scan cells support both normal operation and diagnostic modes which can verify inputs and outputs, test circuit board traces, and check device functions. • Boundary scan devices have at least four extra pins: test data in, test data out, test mode select, and clock. Repeat Segment McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. 10-45 REVIEW • Preliminary Checks • No Output • Reduced Output • Intermittents • Operational Amplifiers • Automated Testing McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved.