Source: https://mokxi.com/teachers/plans/fault-finding-circuits Updated: 2026-11-12 Lesson plan # Troubleshooting like a technician lesson plan Find faults nobody planted for you: power first, half splitting, signal tracing, opens and shorts, failed parts and intermittents. Ends with a repair ticket: three boards, one fault each. 4 chapters, 7 lessons, about 6 hours, no board. Every lesson runs in the browser, with nothing to install. Start a class from this course The unit ## Objectives and materials ### By the end, students can - A method that works on anything, and halving the search with every reading. - Signal tracing, and what an open and a short look like on a meter. - Parts that are not what they say, and faults that come and go. - A repair ticket with three boards on it. ### Materials for the whole unit - Battery: AA, coin cell, LiPo - Bench power supply - Capacitor x 3 - Component tester x 4 - Frequency counter - Full-size breadboard - Function generator - LED x 8 - LM358 dual op-amp - Multimeter x 2 - NE555 timer - Oscilloscope - Resistor x 5 - Slide switch - Transistor (NPN or PNP) x 3 - Voltage regulator Every part is already on the simulator’s bench, so there is nothing to buy or hand out. The counts are the most any one lesson uses, if you build it on real breadboards too. Chapter 1. About 1 h 30 min ## Find it fast A method that works on anything, and halving the search with every reading. Lesson | Time | What students do A method A blinker that does nothing. Work it the way a technician does: symptom, power first, measure against what it should be, fix the cause, verify, and write it down. | 40 min - The ticket - Power first: the battery - Then the rail - Fix the cause - Verify - Write it down Half splitting Eight lights in series, all dark, one bad. Find it in three measurements instead of eight by always measuring in the middle of what is left. | 50 min - Eight lights, all dark - Measure the middle - Split the lower half - Split again - Look closely at LED 6 - Verify - Quick check ### Materials - Battery: AA, coin cell, LiPo - Bench power supply - Capacitor x 2 - Full-size breadboard - LED x 8 - Multimeter x 2 - NE555 timer - Resistor x 3 - Voltage regulator ### Check for understanding Each student finishes "Half splitting" on their own, without opening the hints. The simulator checks 7 of its 7 steps as they go. Then ask each one to explain, in a sentence or two, the last thing it asked of them: "Quick check". Chapter 2. About 1 h 45 min ## Follow the signal Signal tracing, and what an open and a short look like on a meter. Lesson | Time | What students do Signal tracing An amplifier with no output. Check its DC first, then follow the signal stage by stage from the source until it disappears, and replace the part where it died. | 55 min - No output - DC first: is it alive? - Start at the source - Half way: the output - Narrow it: the input pin - Replace C1 - Verify the gain - Quick check Opens and shorts A board with a dead short and an open on it. What each looks like on a meter: a short is zero volts and all the current, an open is all the voltage and no current. Find both and fix them. | 50 min - Everything dead - Power off, then ohms - Find the bridge - Now the open - Bridge the gap - Verify - Quick check ### Materials - Bench power supply - Capacitor x 3 - Full-size breadboard - Function generator - LED x 3 - LM358 dual op-amp - Multimeter x 2 - Resistor x 5 ### Check for understanding Each student finishes "Opens and shorts" on their own, without opening the hints. The simulator checks 7 of its 7 steps as they go. Then ask each one to explain, in a sentence or two, the last thing it asked of them: "Quick check". Chapter 3. About 1 h 45 min ## The hard ones Parts that are not what they say, and faults that come and go. Lesson | Time | What students do Failed parts A transistor switch that will not switch. Read its junctions in circuit, then test the suspect and a spare out of circuit, and sort a drawer of parts that are not what their markings say. | 55 min - Switch on, LED off - Read the base - Out of circuit, on the tester - Test the spare - Fit the right part - The rest of the drawer - A tired capacitor - Quick check Intermittents Faults that come and go. Provoke a cracked joint with a tap test and repair it, then find a flicker that is not a bad part at all but a design with no margin, and fix the design. | 50 min - The hardest tickets - The tap test - Reflow the joint - The other complaint: a flicker - Measure the margin - Fix the margin - Quick check ### Materials - Capacitor - Component tester x 4 - Full-size breadboard - Function generator - LED x 2 - LM358 dual op-amp - Multimeter x 2 - Oscilloscope - Resistor x 4 - Slide switch - Transistor (NPN or PNP) x 3 ### Check for understanding Each student finishes "Intermittents" on their own, without opening the hints. The simulator checks 7 of its 7 steps as they go. Then ask each one to explain, in a sentence or two, the last thing it asked of them: "Quick check". Chapter 4. About 55 min ## Boss A repair ticket with three boards on it. Lesson | Time | What students do Boss: repair three boards A repair ticket with three boards on it, one fault each: a supply putting out the wrong voltage, a blinker that only glows, and a driver whose LED never lights. Measure, fix, verify and write up all three. | 55 min - Board A: measure - Board A: fix - Board B: count it - Board B: fix - Board C: measure - Board C: fix - Verify all three - Write it up ### Materials - Battery: AA, coin cell, LiPo - Capacitor - Frequency counter - Full-size breadboard - LED x 2 - Multimeter x 2 - NE555 timer - Resistor x 5 - Transistor (NPN or PNP) - Voltage regulator ### Check for understanding Each student finishes "Boss: repair three boards" on their own, without opening the hints. The simulator checks 8 of its 8 steps as they go. Then ask each one to explain, in a sentence or two, the last thing it asked of them: "Write it up". Your class ## Teach this unit as a class Start a class from this course and its 7 lessons are assigned in one go, in order. Students join with a six-character code or printed login cards, and each one’s work comes back to you. The class tools are free for 30 days for one class of up to 20 students, with no card. The lessons themselves are free either way. Start a class from this course See the demo class More units ## Other lesson plans Electronics basics 20 lessons, about 10 h. Embedded on the Arduino Uno 16 lessons, about 12 h. Embedded on the ESP32-C3 13 lessons, about 11 h. Embedded on the Raspberry Pi Pico 7 lessons, about 6 h. Build your own fight stick 5 lessons, about 4 h. Embedded on the STM32F411 6 lessons, about 6 h. C++ on a board 13 lessons, about 10 h. Digital logic and memory 4 lessons, about 4 h. 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