EETC Circuit Design & Troubleshooting 2 — Questions and Answers
Question 1: A technician measures 0V across a load resistor in a series circuit. What is the most likely fault?
- The load resistor is shorted
- There is an open circuit upstream of the load (Correct answer)
- The power supply voltage is too high
- The load resistor value is too low
Correct answer: There is an open circuit upstream of the load
An open circuit upstream prevents current flow, resulting in 0V across the load (all voltage drops at the open point).
Question 2: Which filter topology uses an inductor in series and a capacitor in parallel to pass low frequencies?
- High-pass LC filter
- Band-pass filter
- Low-pass LC filter (Correct answer)
- Notch filter
Correct answer: Low-pass LC filter
A low-pass LC filter places the inductor in series (blocks high frequencies) and the capacitor in shunt (bypasses remaining high frequencies to ground).
Question 3: When troubleshooting a circuit with an oscilloscope, you observe a waveform with excessive ripple at the output of a rectifier. What component is most likely faulty?
- The transformer primary winding
- The filter capacitor (Correct answer)
- The rectifier diodes
- The load resistor
Correct answer: The filter capacitor
A deteriorated or open filter capacitor cannot smooth the rectified waveform, causing excessive ripple voltage.
Question 4: What is the purpose of a snubber circuit placed across a relay coil?
- To increase coil inductance
- To suppress voltage spikes caused by inductive kickback (Correct answer)
- To reduce the relay pull-in current
- To filter AC noise from the power supply
Correct answer: To suppress voltage spikes caused by inductive kickback
When a relay coil de-energizes, its inductance produces a large reverse voltage spike; a snubber (RC or diode) clamps this transient.
Question 5: In a voltage divider circuit with R1=10kΩ and R2=10kΩ connected to 24V, what is the output voltage taken across R2?
- 6V
- 12V (Correct answer)
- 18V
- 24V
Correct answer: 12V
Equal resistors split the voltage equally: Vout = 24V × (10k/(10k+10k)) = 12V.
Question 6: A technician finds that a PCB trace is intermittently open at a solder joint. Which troubleshooting technique is most effective for isolating this fault?
- Replacing all components on the board
- Flexing the board while monitoring continuity (Correct answer)
- Measuring supply voltage only
- Replacing the power supply
Correct answer: Flexing the board while monitoring continuity
Physically flexing the board stresses intermittent solder joint cracks, causing them to open and close, revealing the fault location.
Question 7: Which of the following best describes a Thevenin equivalent circuit?
- A current source in parallel with a resistance
- A voltage source in series with a resistance (Correct answer)
- Two resistors in a bridge configuration
- A capacitor in series with an inductor
Correct answer: A voltage source in series with a resistance
Thevenin's theorem states any linear network can be reduced to a single voltage source (Vth) in series with a single resistance (Rth).
EETC Circuit Design & Troubleshooting 2
A technician measures 0V across a load resistor in a series circuit.
What is the most likely fault?