EETC Circuit Design & Troubleshooting 3 — Questions and Answers
Question 1: A class-A amplifier operates with the transistor conducting for what portion of the input signal cycle?
- 25%
- 50%
- 75%
- 100% (Correct answer)
Correct answer: 100%
In class-A operation, the transistor is biased to conduct continuously throughout the entire 360° of the input signal cycle.
Question 2: What does a megohmmeter (megger) primarily measure in electrical troubleshooting?
- Very low resistances in motor windings
- Insulation resistance between conductors and ground (Correct answer)
- High-frequency impedance of capacitors
- DC winding resistance of transformers
Correct answer: Insulation resistance between conductors and ground
A megohmmeter applies high DC voltage (typically 500–5000V) to measure insulation resistance, detecting degraded or failed insulation.
Question 3: In a full-wave bridge rectifier, how many diodes conduct simultaneously during each half-cycle?
- 1
- 2 (Correct answer)
- 3
- 4
Correct answer: 2
During each half-cycle of a bridge rectifier, current flows through exactly two diodes—one on the top and one on the bottom of the bridge.
Question 4: When designing a PCB for high-frequency circuits, why should ground planes be used?
- To increase trace impedance
- To reduce electromagnetic interference and provide a low-inductance return path (Correct answer)
- To increase the physical size of the board
- To eliminate the need for bypass capacitors
Correct answer: To reduce electromagnetic interference and provide a low-inductance return path
Ground planes provide a low-impedance, low-inductance return path for currents and reduce EMI by shielding signal traces.
Question 5: A technician notices that a voltage regulator IC is very hot to the touch even with a minimal load. What is the most likely cause?
- The output capacitor is too large
- Excessive input-to-output voltage differential across the regulator (Correct answer)
- The load resistance is too high
- The output voltage is set too low
Correct answer: Excessive input-to-output voltage differential across the regulator
Linear regulators dissipate power equal to (Vin − Vout) × Iload, so a large input-to-output differential causes high heat even at low currents.
Question 6: In an RC timing circuit using a 555 timer in monostable mode, increasing the resistor value will:
- Decrease the output pulse width
- Increase the output pulse width (Correct answer)
- Change the frequency but not pulse width
- Have no effect on timing
Correct answer: Increase the output pulse width
The output pulse width in monostable mode is t = 1.1 × R × C; increasing R directly increases the time constant and pulse width.
Question 7: What troubleshooting method involves injecting a known signal at a circuit's input and tracing it toward the output?
- Signal tracing from output to input
- Signal injection from input to output (Correct answer)
- Half-splitting technique
- Component substitution
Correct answer: Signal injection from input to output
Signal injection introduces a test signal at the input and follows it stage by stage toward the output, identifying where the signal is lost or distorted.
EETC Circuit Design & Troubleshooting 3
A class-A amplifier operates with the transistor conducting for what portion of the input signal cycle?