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10-1
Electronics
Principles & Applications
Eighth Edition
Charles A. Schuler
Chapter 10
Troubleshooting
(student version)
©2013
McGraw-Hill
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10-2
INTRODUCTION
• Preliminary Checks
• No Output
• Reduced Output
• Intermittents
• Operational Amplifiers
• Automated Testing
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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.
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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.
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10-5
GOAL
• Good troubleshooting
• Observe the symptoms
• Analyze the possible causes
• Limit the possibilities
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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
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Inputs
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10-7
Don’t forget to check for blown fuses!
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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
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10-9
Electrostatic Discharge (ESD)
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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
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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
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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
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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.
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10-14
SIGNAL INJECTION METHOD
STAGE 1
STAGE 2
STAGE 3
STAGE 4
SIGNAL GENERATOR
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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
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10-16
SIGNAL TRACING METHOD
(Divide and conquer works here too.)
STAGE 1
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STAGE 2
STAGE 3
STAGE 4
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10-17
Additional paths cause
the reading to be low.
C
V
B
mA
E
R1
In-circuit ohmmeter testing can be misleading.
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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
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10-18
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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
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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.
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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
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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
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Short causes loss of B-E bias
and transistor is cutoff
(depends on prior stage)
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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).
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10-24
If this is open,
the amplifier
voltages are 0.
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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?
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10-26
If this is open,
the transistor
approaches
saturation.
Will the collector voltage be high or low?
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10-27
If this is open,
the transistor
collector goes
to zero volts.
Will the base voltage be off very far?
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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
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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
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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.
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10-31
VERIFYING POWER OUTPUT
AMPLIFIER
DUMMY
LOAD
SIGNAL GENERATOR
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10-32
CHECKING FOR DISTORTION
AMPLIFIER
Crossover
TRIANGLE GENERATOR
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Clipping
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10-33
Making intermittents show up
•
•
•
•
•
•
•
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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
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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
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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?
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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
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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.
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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
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10-40
More boundary scan functions
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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
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10-43
Analog boundary scan
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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
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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.