© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 10-1 Electronics Principles & Applications Eighth Edition Chapter 10 Troubleshooting (student version) Charles A. Schuler ©2013

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 10-2 Preliminary Checks No Output Reduced Output Intermittents Operational Amplifiers Automated Testing INTRODUCTION

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 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.

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 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.

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 10-5 GOAL Good troubleshooting Observe the symptoms Analyze the possible causes Limit the possibilities

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 10-6 A System Point of View Inputs Network Other hardware Software Power? Controls Connectors Symptoms? Diagnostics * adjust framostat * synthesizer off * buy low * sell high Causes? Components

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 10-7 Don’t forget to check for blown fuses!

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 10-8 R LOAD SYMPTOMS V LOAD = 0 V LOAD < NORMAL V LOAD > NORMAL FAULTS ZENER OPEN ZENER SHORTED R 1 OPEN R 1 > NORMAL C SHORTED V IN < NORMAL R1R1 V IN V IN = 0 C I LOAD > NORMAL C OPEN V LOAD SHOWS NOISE

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 10-9 Electrostatic Discharge (ESD)

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill ESD 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 PREVENTION

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 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

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 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

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 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.

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill SIGNAL INJECTION METHOD STAGE 1 STAGE 2 STAGE 3 STAGE 4 SIGNAL GENERATOR

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill SIGNAL INJECTION METHOD (another approach) STAGE 1 STAGE 2 STAGE 3 STAGE 4 SIGNAL GENERATOR Some technicians prefer the “divide and conquer” approach as it often saves time. Start in the middle.

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill SIGNAL TRACING METHOD (Divide and conquer works here too.) STAGE 1 STAGE 2 STAGE 3 STAGE 4

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill V mA E B C R1R1 In-circuit ohmmeter testing can be misleading. Additional paths cause the reading to be low. 

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill SIGNAL COMPARISON METHOD (Divide and conquer works here too.) RIGHT STAGE 1 RIGHT STAGE 2 RIGHT STAGE 3 RIGHT STAGE 4 LEFT STAGE 1 LEFT STAGE 2 LEFT STAGE 3 LEFT STAGE 4

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 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

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 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.

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill If any of these are open, there are no dc voltage errors. Open causes decrease in gain Open causes loss of signal Open might cause hum or noise

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill If any of these are shorted, there are dc errors. Short causes increase in transistor current Short causes loss of B-E bias and transistor is cutoff (depends on prior stage) Short causes amplifier voltages to be zero

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 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).

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill If this is open, the amplifier voltages are 0.

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill If either of these is open, the transistor is in cutoff. Which of these two faults will produce a non-zero emitter voltage?

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill If this is open, the transistor approaches saturation. Will the collector voltage be high or low?

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill If this is open, the transistor collector goes to zero volts. Will the base voltage be off very far?

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 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

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 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

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 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.

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill VERIFYING POWER OUTPUT SIGNAL GENERATOR DUMMY LOAD AMPLIFIER

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill CHECKING FOR DISTORTION TRIANGLE GENERATOR AMPLIFIER Crossover Clipping

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill Making intermittents show up 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. McGraw-Hill V 5 k  Here’s a solution: add a negative voltage to cancel the positive dc offset of the source. 100 k  1 k  1 V DC 1 k  RLRL Suppose a signal source has a dc component that must be eliminated but a coupling capacitor is not acceptable.

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill k  1 k  1 V DC 1 k  RLRL Suppose the output voltage is at negative saturation. - 5 V 5 k  - 12 V Could the 5 k rr esistor be open? Could the - 5 V supply be at fault? What else could be wrong?

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 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

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 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

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 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.

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill Test data in Test data out Virtual nails 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. Boundary scan functions Scan chain

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill More boundary scan functions

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill Each boundary scan chip pin is connected to cell. Scan chain Core Cell Normal output Serial output Serial input Normal input (from core) When the normal input is routed to the normal output, the chip works as if there was no scan function. The normal output can be driven by the serial input. The serial output can be driven by the serial input.

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill SN74BCT244 SN74BCT8244A Octal buffer/driver Test data out Test data in Test clock Test mode select Boundary scan version

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill Analog boundary scan

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 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

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill Preliminary Checks No Output Reduced Output Intermittents Operational Amplifiers Automated Testing REVIEW