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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.McGraw-Hill
10-1
ElectronicsElectronics
Principles & ApplicationsPrinciples & ApplicationsEighth EditionEighth Edition
Chapter 10Troubleshooting(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 segmentis preceded by a Concept Preview slide and is followed by aConcept Review slide. When you reach a Concept Reviewslide, you can return to the beginning of that segment byclicking on the Repeat Segment button. This will allow youto 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
10-6A System Point of View
Inputs
Network
Other hardware
Software
Power?
Controls
Connectors
Symptoms?
Diagnostics
* adjust framostat
* synthesizer off
* buy low* sell high
Causes?Components
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Don’t forget to check for blown fuses!
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RLOAD
SYMPTOMS
VLOAD = 0
VLOAD < NORMAL
VLOAD > NORMAL
FAULTS
ZENER OPEN
ZENER SHORTED
R1 OPEN
R1 > NORMAL
C SHORTED
VIN < NORMAL
R1
VIN
VIN = 0
C
ILOAD > NORMAL
C OPENVLOAD SHOWS NOISE
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Electrostatic Discharge (ESD)
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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
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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 becaused by hardware or _________. software
Some solid-state devices are easily damagedby ____________ discharge. electrostatic
Technicians sometimes wear a wrist strapto prevent _________. ESD
© 2013 The McGraw-Hill Companies, Inc. All rights reserved.McGraw-Hill
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
© 2013 The McGraw-Hill Companies, Inc. All rights reserved.McGraw-Hill
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 STAGE 3 STAGE 4
SIGNAL GENERATOR
Some technicians prefer the “divide
and conquer” approach as it
often saves time.
Start in the middle.
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SIGNAL TRACING METHOD (Divide and conquer works here too.)
STAGE 1 STAGE 2 STAGE 3 STAGE 4
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10-17
0
V
mA EB
C
R1
In-circuit ohmmeter testing can be misleading.
Additional paths causethe reading to be low.
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SIGNAL COMPARISON METHOD(Divide and conquer works here too.)
RIGHTSTAGE 1
RIGHTSTAGE 2
RIGHTSTAGE 3
RIGHTSTAGE 4
LEFTSTAGE 1
LEFTSTAGE 2
LEFTSTAGE 3
LEFTSTAGE 4
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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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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
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10-22
If any of these are shorted, there are dc errors.
Short causes increase in
transistor current
Short causes loss of B-E biasand transistor is cutoff
(depends on prior stage)
Short causes amplifier voltages to be zero
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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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If this is open,the amplifier
voltages are 0.
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If either ofthese is open,the transistor
is in cutoff.
Which of these two faults will produce a non-zero emitter voltage?
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If this is open,the transistorapproachessaturation.
Will the collector voltage be high or low?
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If this is open,the transistorcollector goesto zero volts.
Will the base voltage be off very far?
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Component level troubleshooting quiz
Ohmmeter troubleshooting can be misleadingwhen performed _____ a circuit. in
Dc voltage errors are usually not caused by_________ coupling capacitors. open
A shorted coupling capacitor could cause theQ-point to move to cutoff or ______. saturation
When a base bias resistor opens, the Q-point__________ changes. always
Stage-by-stage verification with an oscilloscopeis called signal ____________. tracing
© 2013 The McGraw-Hill Companies, Inc. All rights reserved.McGraw-Hill
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
© 2013 The McGraw-Hill Companies, Inc. All rights reserved.McGraw-Hill
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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VERIFYING POWER OUTPUT
SIGNAL GENERATOR
DUMMYLOAD
AMPLIFIER
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CHECKING FOR DISTORTION
TRIANGLE GENERATOR
AMPLIFIER
Crossover
Clipping
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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
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- 5 V
5 k
Here’s a solution: add a negative voltageto cancel the positive dc offset of the source.
100 k
1 k
1 VDC
1 k
RL
Suppose a signal source has a dc component that must beeliminated but a coupling capacitor is not acceptable.
© 2013 The McGraw-Hill Companies, Inc. All rights reserved.McGraw-Hill
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100 k
1 k
1 VDC
1 k
RL
Suppose the output voltage is at negative saturation.
- 5 V
5 k
- 12 V
Could the 5 kresistor 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
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Verification and intermittent quiz
Amplifier power output is best measuredusing a ________ load. dummy
The waveform that makes it easy to seeamplifier distortion is the _______. triangle
Intermittents caused by poor connections maybe located by using __________. vibration
Some intermittents can be made to appear bychanging temperature or supply _____. voltage
When an op amp shows dc output error, checkfirst for dc _________ error. input
© 2013 The McGraw-Hill Companies, Inc. All rights reserved.McGraw-Hill
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
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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.
© 2013 The McGraw-Hill Companies, Inc. All rights reserved.McGraw-Hill
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Test data in
Test data out
Virtualnails
During a scan,devices can be
checked forproper function.
During a scan,I/O ports can be
checked forproper function.
During a scan,circuit traces can be
checked forproper function.
Boundary scan functions
Scanchain
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More boundary scan functions
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Each boundary scan chip pin is connected to cell.
Scan chain
Core
CellNormal output
Serial output
Serial input
Normal input(from core)
When the normal input is routed tothe normal output, the chip worksas if there was no scan function.
The normal output can bedriven by the serial input.The serial output can be
driven by the serial input.
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SN
74B
CT
244
SN
74B
CT
8244
A
Octal buffer/driver
Test data out Test data in
Test clockTest mode select
Boundary scan version
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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
© 2013 The McGraw-Hill Companies, Inc. All rights reserved.McGraw-Hill
10-45
• Preliminary Checks• No Output• Reduced Output• Intermittents• Operational Amplifiers• Automated Testing
REVIEW
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