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ECE 2799 Electronic Troubleshooting Strategies

ECE 2799 Electronic Troubleshooting Strategies. Prof. Bitar Last Update: 04/15/10. Electronic Troubleshooting Strategies. Divide and Conquer Bait and Switch Time Warp Wiggle Test Cut Out the Middle Man Show Me the Voltage - Open Circuit Voltage Test (OCVT)

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ECE 2799 Electronic Troubleshooting Strategies

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

  2. Electronic Troubleshooting Strategies • Divide and Conquer • Bait and Switch • Time Warp • Wiggle Test • Cut Out the Middle Man • Show Me the Voltage - Open Circuit Voltage Test (OCVT) • Follow the Current - Short Circuit Current Test (SCCT) • Lose Control (Feedback Systems)

  3. 1. “Divide and Conquer” • 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

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

  5. And How Neatly You Laid it Out…

  6. “The Clapper” – DC Bias Questions… • DC Bias Questions: • 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?

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

  8. Voltage Waveforms …

  9. 2. “Bait and Switch” • 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)

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

  11. Consult the Spec Sheet

  12. Possible Simulation Model

  13. Repeat for Output Speaker Source: www.digikey.com

  14. Possible Speaker Models • 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?

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

  16. LM555 Timer Example Source: www.national.com

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

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

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

  20. Open Circuit Voltage Example

  21. 7. “Follow the Current”Short Circuit Current Test (SCCT) • 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

  22. Short Circuit Current Example

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

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