ECE 2799 Electronic Troubleshooting Strategies Prof. Bitar Last Update: 04/15/10

Electronic Troubleshooting Strategies 1.Divide and Conquer 2.Bait and Switch 3.Time Warp 4.Wiggle Test 5.Cut Out the Middle Man 6.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” Isolate each Block of a System Isolate each Block of a System Verify the Power to each Block Verify the Power to each Block Verify the DC Bias Verify the DC Bias Verify the Proper Signal Input and Output Verify the Proper Signal Input and Output Applies to Breadboard Applies to Breadboard Applies to Simulation Applies to Simulation Applies to Prototype Construction Applies to Prototype Construction

Remember this circuit from ECE 2011? Acoustic Sensor High Pass Filter Amplifier (Gain=75) Peak Detector ComparatorLED

And How Neatly You Laid it Out…

“The Clapper” – DC Bias Questions… DC Bias Questions: DC Bias Questions: What average DC voltage would you expect to measure at nodes V1, V2, V3, and V4? 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 V1 = 0V, what could be wrong? What if V1 = 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 this? If the LED is on all the time, what could cause 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: Can you anticipate what the signals V1, V2, V3 and V4 should look like on a scope? Qualitatively? Quantitatively? 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? 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 …

2. “Bait and Switch” Substitute for Sensor Input Substitute for Sensor Input Potentiometer Potentiometer Variable Power Supply Variable Power Supply Thevenin Equivalent Thevenin Equivalent Substitute for Load Output Substitute for Load Output Equivalent Load Impedance (Resistance) Equivalent Load Impedance (Resistance) Can Apply I/O Substitution to all Functional Blocks Can Apply I/O Substitution to all Functional Blocks Be Sure to Match I/O Resistance (R IN and R OUT ) Be Sure to Match I/O Resistance (R IN and R OUT )

What could replace the microphone for testing purposes? Things to Consider: Things to Consider: DC Bias DC Bias Amplitude of AC Signal Amplitude of AC Signal Internal Source Impedance Internal Source Impedance

Consult the Spec Sheet

Possible Simulation Model

Repeat for Output Speaker Source:

Possible Speaker Models Under what conditions would you use the simper model? Or the more complex one? 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? In lab, if using a “Dummy Load” what concerns should be considered?

3. “Time Warp” Applies to Timing Functions Governed by: Applies to Timing Functions Governed by: RC Time Constants RC Time Constants Crystal Oscillators Crystal Oscillators Digital Counters Digital Counters

LM555 Timer Example Source:

4. “Wiggle Test” Intermittent Mechanical Connections Intermittent Mechanical Connections #1 Cause of Electronic Troubleshooting Problems #1 Cause of Electronic Troubleshooting Problems Ford “Wiggle Test” Ford “Wiggle Test” Be Methodical Be Methodical Isolate and Stress Each Connection Isolate and Stress Each Connection

5. “Cut Out the Middle Man” Applies to Multiple Connection Systems Applies to Multiple Connection Systems Apply Bypass Techniques to Isolate Problems Apply Bypass Techniques to Isolate Problems Often Applied to Vehicle Harnesses and House Wiring Often Applied to Vehicle Harnesses and House Wiring

6. “Show Me the Voltage” Open Circuit Voltage Test (OCVT) In a Series Circuit the Greatest Voltage Drop Occurs Across the Largest Resistance In a Series Circuit the Greatest Voltage Drop Occurs Across the Largest Resistance Therefore, an Open Circuit will Have the Most Voltage Across It Therefore, an Open Circuit will Have the Most Voltage Across It

Open Circuit Voltage Example

7. “Follow the Current” Short Circuit Current Test (SCCT) In a Parallel Circuit the Greatest Current Flows Through the Smallest Resistance In a Parallel Circuit the Greatest Current Flows Through the Smallest Resistance Therefore, a Short Circuit will Have the Most Current Through It 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 Use the Current Limiting Feature of your Power Supply to Prevent Damage to Components

Short Circuit Current Example

8. “Lose Control” Applies to Systems With Feedback Applies to Systems With Feedback Cut the Control Cut the Control Substitute Test Control Signal Substitute Test Control Signal Verify Proper Feedback Signal Verify Proper Feedback Signal Watch Out for System Runaway! Watch Out for System Runaway!