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

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

GOAL Good troubleshooting Observe the symptoms Analyze the possible causes Limit the possibilities

A System Point of View Symptoms? Causes? Other hardware Components Diagnostics Other hardware * adjust framostat * synthesizer off * buy low Symptoms? * sell high Causes? Components Software Power? Network Controls Connectors Inputs

SYMPTOMS FAULTS VLOAD = 0 VIN = 0 VIN < NORMAL VLOAD < NORMAL R1 OPEN VLOAD > NORMAL R1 > NORMAL VLOAD SHOWS NOISE C OPEN C SHORTED VIN ZENER OPEN R1 RLOAD ZENER SHORTED C ILOAD > NORMAL

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

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

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

SIGNAL TRACING METHOD STAGE 1 STAGE 2 STAGE 3 STAGE 4

Additional paths cause the reading to be low.  C V B E mA R1 In-circuit ohmmeter testing can be misleading.

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

If any of these are open, there are no dc voltage errors. Open might cause hum or noise If any of these are open, there are no dc voltage errors. Open causes loss of signal Open causes decrease in gain

If any of these are shorted, there are dc errors. Short causes amplifier voltages to be zero If any of these are shorted, there are dc errors. Short causes loss of B-E bias and transistor is cutoff (depends on prior stage) Short causes increase in transistor current

If this is open, the amplifier voltages are 0.

Which of these two faults will produce a non-zero emitter voltage? 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

Verifying Power Output AMPLIFIER DUMMY LOAD SIGNAL GENERATOR

Checking for Distortion AMPLIFIER Crossover Clipping TRIANGLE GENERATOR

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

Suppose a signal source has a dc component that must be eliminated but a coupling capacitor is not acceptable. - 5 V 5 kW Here’s a solution: add a negative voltage to cancel the positive dc offset of the source. 1 kW 100 kW 1 VDC RL 1 kW

- 12 V - 5 V Suppose the output voltage is at negative saturation. Could the 5 kW resistor be open? Could the - 5 V supply be at fault? - 5 V 5 kW 1 kW 100 kW - 12 V 1 VDC RL 1 kW 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

Boundary Scan Functions During a scan, devices can be checked for proper function. During a scan, I/O ports can be checked for proper function. Virtual nails During a scan, circuit traces can be checked for proper function. Scan chain Test data in Test data out

Each boundary scan chip pin is connected to cell. Normal input (from core) Serial output The serial output can be driven by the serial input. Cell Normal output 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. Serial input Scan chain

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

Analog Boundary Scan

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