Transcript EE2799 – ECE Design

ECE 2799
Electronic Troubleshooting
Strategies
Prof. Bitar
Last Update: 04/15/10
Electronic Troubleshooting Strategies
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6.
Divide and Conquer
Bait and Switch
Time Warp
Wiggle Test
Cut Out the Middle Man
Show Me the Voltage - Open Circuit
Voltage Test (OCVT)
7. Follow the Current - Short Circuit
Current Test (SCCT)
8. Lose Control (Feedback Systems)
1. “Divide and Conquer”
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Isolate each Block of a System
Verify the Power to each Block
Verify the DC Bias
Verify the Proper Signal Input
and Output
Applies to Breadboard
Applies to Simulation
Applies to Prototype Construction
Remember this circuit from ECE 2011?
Acoustic
Sensor
High Pass
Filter
Amplifier
(Gain=75)
Peak
Detector
Comparator
LED
And How Neatly You Laid it Out…
“The Clapper” – DC Bias Questions…
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DC Bias Questions:
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What average DC voltage would you expect to measure
at nodes V1, V2, V3, and V4?
If V1 = 0V, what could be wrong? What if V1 = 9V?
If V3 = 7.5VDC (or -7.5V), what could cause this?
If the LED is on all the time, what could cause this?
What if the LED is OFF all of the time?
Signal Path Questions…
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Signal Path Questions:
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Can you anticipate what the signals V1, V2, V3 and V4
should look like on a scope? Qualitatively? Quantitatively?
What is similar about V1 & V2? What is different?
How about V2 & V3?
V3 & V4?
What about the final output?
Voltage Waveforms …
2. “Bait and Switch”
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Substitute for Sensor Input
 Potentiometer
 Variable Power Supply
 Thevenin Equivalent
Substitute for Load Output
 Equivalent Load Impedance (Resistance)
Can Apply I/O Substitution to all Functional Blocks
Be Sure to Match I/O Resistance (RIN and ROUT)
What could replace the
microphone for testing purposes?
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Things to Consider:
 DC Bias
 Amplitude of AC Signal
 Internal Source
Impedance
Consult the Spec Sheet
Possible Simulation Model
10mVpk
1kHz
4.5V
+
2.2k
Vac
VBIAS
Rs
Repeat for Output
Speaker
Source: www.digikey.com
Possible Speaker Models
R1
L1
RL
8 Ohms
R2
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L2
C1
Under what conditions would you use
the simper model? Or the more
complex one?
In lab, if using a “Dummy Load” what
concerns should be considered?
3. “Time Warp”
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Applies to Timing Functions
Governed by:
 RC Time Constants
 Crystal Oscillators
 Digital Counters
LM555 Timer Example
T  ( RA  2RB )  C  ln( 2)
1
fC 
( RA  2 RB )  C  ln( 2)
Source: www.national.com
4. “Wiggle Test”
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Intermittent Mechanical Connections
#1 Cause of Electronic Troubleshooting
Problems
Ford “Wiggle Test”
Be Methodical
Isolate and Stress Each Connection
5. “Cut Out the Middle Man”
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Applies to Multiple Connection Systems
Apply Bypass Techniques to Isolate
Problems
Often Applied to Vehicle Harnesses and
House Wiring
6. “Show Me the Voltage”
Open Circuit Voltage Test (OCVT)
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In a Series Circuit the Greatest Voltage
Drop Occurs Across the Largest Resistance
Therefore, an Open Circuit will Have the
Most Voltage Across It
Open Circuit Voltage Example
VM1 0V
+
R1 1k
R2 1k
R3 1k
V
R4 1k
R5 1k
VBA T 12
VM1 12V
+
R1 1k
VBA T 12
R2 1k
R3 1k
R4 1k
V
R5 1k
7. “Follow the Current”
Short Circuit Current Test (SCCT)
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In a Parallel Circuit the Greatest Current
Flows Through the Smallest Resistance
Therefore, a Short Circuit will Have the
Most Current Through It
Use the Current Limiting Feature of your
Power Supply to Prevent Damage to
Components
Short Circuit Current Example
R3 1k
VBA T 12
R2 1k
R1 1k
R4 1
AM1 11. 96mA
R3 1k
R2 1k
VBA T 12
R1 1k
R4 1
AM1 12A
8. “Lose Control”
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Applies to Systems With Feedback
Cut the Control
Substitute Test Control Signal
Verify Proper Feedback Signal
Watch Out for System Runaway!