Electronics Principles & Applications Sixth Edition Chapter 10 Troubleshooting (student version) ©2003 Glencoe/McGraw-Hill Charles A. Schuler

Preliminary Checks No Output Reduced Output Intermittents Operational Amplifiers Automated Testing INTRODUCTION

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.

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.

GOAL G ood troubleshooting O bserve the symptoms A nalyze the possible causes L imit the possibilities

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

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

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

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

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

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.

SIGNAL INJECTION METHOD STAGE 1 STAGE 2 STAGE 3 STAGE 4 SIGNAL GENERATOR

SIGNAL TRACING METHOD STAGE 1 STAGE 2 STAGE 3 STAGE 4

0 V mA E B C R1R1 In-circuit ohmmeter testing can be misleading. Additional paths cause the reading to be low. 

SIGNAL COMPARISON METHOD RIGHT STAGE 1 RIGHT STAGE 2 RIGHT STAGE 3 RIGHT STAGE 4 LEFT STAGE 1 LEFT STAGE 2 LEFT STAGE 3 LEFT STAGE 4

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

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.

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

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

If this is open, the amplifier voltages are 0.

If either of these is open, the transistor is in cutoff. Which of these two faults will produce a non-zero emitter voltage?

If this is open, the transistor approaches saturation. Will the collector voltage be high or low?

If this is open, the transistor collector goes to zero volts. Will the base voltage be off very far?

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

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

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.

Verifying Power Output SIGNAL GENERATOR DUMMY LOAD AMPLIFIER

Checking for Distortion TRIANGLE GENERATOR AMPLIFIER Crossover Clipping

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

- 5 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.

100 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?

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

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

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.

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

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.

SN74BCT244 SN74BCT8244A Octal buffer/driver Test data out Test data in Test clock Test mode select Boundary scan version

Analog Boundary Scan

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

REVIEW Preliminary Checks No Output Reduced Output Intermittents Operational Amplifiers Automated Testing