ECE 2799 ECE 2799

Electronic Troubleshooting Electronic Troubleshooting StrategiesStrategies

Prof. BitarProf. BitarLast Update: 04/15/10Last Update: 04/15/10

Electronic Troubleshooting Electronic Troubleshooting StrategiesStrategies

1.1. Divide and ConquerDivide and Conquer2.2. Bait and SwitchBait and Switch3.3. Time WarpTime Warp4.4. Wiggle TestWiggle Test5.5. Cut Out the Middle ManCut Out the Middle Man6.6. Show Me the Voltage - Open Show Me the Voltage - Open

Circuit Voltage Test (OCVT) Circuit Voltage Test (OCVT) 7.7. Follow the Current - Short Circuit Follow the Current - Short Circuit

Current Test (SCCT) Current Test (SCCT) 8.8. Lose Control (Feedback Systems)Lose Control (Feedback Systems)

1. “Divide and Conquer”1. “Divide and Conquer” Isolate each Block of a SystemIsolate each Block of a System Verify the Power to each BlockVerify the Power to each Block Verify the DC BiasVerify the DC Bias Verify the Proper Signal Verify the Proper Signal

Input and Output Input and Output Applies to BreadboardApplies to Breadboard Applies to SimulationApplies to Simulation Applies to Prototype Construction Applies to Prototype Construction

Remember this circuit from ECE Remember this circuit from ECE 2011?2011?

AcousticSensor

High PassFilter

Amplifier(Gain=75)

PeakDetector

Comparator LED

And How Neatly You Laid it Out…

““The Clapper” – DC Bias The Clapper” – DC Bias Questions…Questions…

DC Bias Questions:DC Bias Questions: What average DC voltage would you expect to What average DC voltage would you expect to

measure at nodes V1, V2, V3, and V4? measure at nodes V1, V2, V3, and V4? If V1 = 0V, what could be wrong? What if V1 = If V1 = 0V, what could be wrong? What if V1 =

9V? 9V? If V3 = 7.5VDC (or -7.5V), what could cause this?If V3 = 7.5VDC (or -7.5V), what could cause this? If the LED is on all the time, what could cause If the LED is on all the time, what could cause

this?this? What if the LED is OFF all of the time?What if the LED is OFF all of the time?

Signal Path Questions…Signal Path Questions…

Signal Path Questions:Signal Path Questions: Can you anticipate what the signals V1, V2, V3 and Can you anticipate what the signals V1, V2, V3 and

V4 should look like on a scope? Qualitatively? V4 should look like on a scope? Qualitatively? Quantitatively? Quantitatively?

What is similar about V1 & V2? What is different?What is similar about V1 & V2? What is different? How about V2 & V3?How about V2 & V3? V3 & V4?V3 & V4? What about the final output?What about the final output?

Voltage Waveforms …Voltage Waveforms …

2. “Bait and Switch”2. “Bait and Switch” Substitute for Sensor InputSubstitute for Sensor Input

PotentiometerPotentiometer Variable Power SupplyVariable Power Supply Thevenin EquivalentThevenin Equivalent

Substitute for Load OutputSubstitute for Load Output Equivalent Load Impedance (Resistance)Equivalent Load Impedance (Resistance)

Can Apply I/O Substitution to all Functional Can Apply I/O Substitution to all Functional BlocksBlocks

Be Sure to Match I/O Resistance (RBe Sure to Match I/O Resistance (RININ and R and ROUTOUT))

What could replace the What could replace the microphone for testing microphone for testing

purposes?purposes? Things to Consider:Things to Consider:

DC BiasDC Bias Amplitude of AC Amplitude of AC

SignalSignal Internal Source Internal Source

Impedance Impedance

Consult the Spec SheetConsult the Spec Sheet

Possible Simulation ModelPossible Simulation Model

+

VacRs

VBIAS

10mVpk1kHz

4.5V

2.2k

Repeat for Output Repeat for Output SpeakerSpeaker

Source: www.digikey.comSource: www.digikey.com

Possible Speaker ModelsPossible Speaker ModelsR1

L1

R2 L2 C1

RL

8 Ohms

Under what conditions would you Under what conditions would you use the simper model? Or the use the simper model? Or the more complex one?more complex one?

In lab, if using a “Dummy Load” In lab, if using a “Dummy Load” what concerns should be what concerns should be considered?considered?

3. “Time Warp”3. “Time Warp”

Applies to Timing Applies to Timing Functions Governed by:Functions Governed by: RC Time ConstantsRC Time Constants Crystal OscillatorsCrystal Oscillators Digital CountersDigital Counters

LM555 Timer ExampleLM555 Timer Example

Source: www.national.comSource: www.national.com

)2ln()2(

1

CRRf

BAC

)2ln()2( CRRT BA

4. “Wiggle Test”4. “Wiggle Test”

Intermittent Mechanical Intermittent Mechanical Connections Connections

#1 Cause of Electronic #1 Cause of Electronic Troubleshooting ProblemsTroubleshooting Problems

Ford “Wiggle Test”Ford “Wiggle Test” Be MethodicalBe Methodical Isolate and Stress Each ConnectionIsolate and Stress Each Connection

5. “Cut Out the Middle 5. “Cut Out the Middle Man”Man”

Applies to Multiple Connection Applies to Multiple Connection SystemsSystems

Apply Bypass Techniques to Isolate Apply Bypass Techniques to Isolate ProblemsProblems

Often Applied to Vehicle Harnesses Often Applied to Vehicle Harnesses and House Wiringand House Wiring

6. “Show Me the Voltage” 6. “Show Me the Voltage” Open Circuit Voltage Test Open Circuit Voltage Test (OCVT)(OCVT)

In a Series Circuit the Greatest In a Series Circuit the Greatest Voltage Drop Occurs Across the Voltage Drop Occurs Across the Largest ResistanceLargest Resistance

Therefore, an Open Circuit will Have Therefore, an Open Circuit will Have the Most Voltage Across Itthe Most Voltage Across It

Open Circuit Voltage Open Circuit Voltage ExampleExample

VBAT 12

R1 1k R2 1k R3 1k R4 1k R5 1kV+

VM1

VBAT 12

R1 1k R2 1k R3 1k R4 1k R5 1kV+

VM1 12V

0V

7. “Follow the Current”7. “Follow the Current”Short Circuit Current Test Short Circuit Current Test (SCCT)(SCCT) In a Parallel Circuit the Greatest In a Parallel Circuit the Greatest

Current Flows Through the Smallest Current Flows Through the Smallest ResistanceResistance

Therefore, a Short Circuit will Have Therefore, a Short Circuit will Have the Most Current Through Itthe Most Current Through It

Use the Current Limiting Feature of Use the Current Limiting Feature of your Power Supply to Prevent your Power Supply to Prevent Damage to ComponentsDamage to Components

Short Circuit Current Short Circuit Current ExampleExample

VBAT 12 R1

1k

R2

1k

R3

1k

AM1

R4 1

VBAT 12 R1

1k

R2

1k

R3

1k

AM1

R4 1

12A

11.96mA

8. “Lose Control”8. “Lose Control”

Applies to Systems With FeedbackApplies to Systems With Feedback Cut the ControlCut the Control Substitute Test Control SignalSubstitute Test Control Signal Verify Proper Feedback SignalVerify Proper Feedback Signal Watch Out for System Runaway!Watch Out for System Runaway!