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

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

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

4. 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

5. 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

6. 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

7. 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

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

9. SIGNAL TRACING METHOD
STAGE 1
STAGE 2
STAGE 3
STAGE 4

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

11. 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

12. 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

13. 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

14. If this is open,
the amplifier
voltages are 0.

15. 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?

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

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

18. 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

19. Verifying Power Output
AMPLIFIER
DUMMY
LOAD
SIGNAL GENERATOR

20. Checking for Distortion
AMPLIFIER
Crossover
Clipping
TRIANGLE GENERATOR

21. 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

22. 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

23. - 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?

24. 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

25. 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

26. 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

27. 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

28. Analog Boundary Scan

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