ISCET Component-Level Troubleshooting 3 — Questions and Answers
Question 1: A technician suspects a leaky electrolytic capacitor. Which symptom best supports this diagnosis?
- Infinite resistance in both directions
- Lower than expected resistance reading on ohmmeter (Correct answer)
- No deflection on ohmmeter needle
- Correct capacitance value on LCR meter
Correct answer: Lower than expected resistance reading on ohmmeter
A leaky capacitor has internal resistance paths causing lower-than-expected resistance readings, indicating dielectric breakdown.
Question 2: What is the primary purpose of an isolation transformer when troubleshooting line-powered equipment?
- To step up voltage for testing
- To prevent shock by isolating the chassis from AC line ground (Correct answer)
- To filter high-frequency noise
- To convert AC to DC
Correct answer: To prevent shock by isolating the chassis from AC line ground
An isolation transformer breaks the direct connection between the AC line and the equipment chassis, preventing shock hazards during testing.
Question 3: A zener diode in a voltage regulator circuit measures 0 V across it under load. What fault is indicated?
- Zener is operating normally
- Zener is shorted (Correct answer)
- Zener is open
- Load resistance is too high
Correct answer: Zener is shorted
A shorted zener diode will drop 0 V, collapsing the regulated output voltage to near zero.
Question 4: When using signal injection to troubleshoot an audio amplifier, where should you begin injecting the test signal?
- At the speaker output
- At the final power amplifier stage
- At the input of the first stage (Correct answer)
- At the power supply filter capacitor
Correct answer: At the input of the first stage
Signal injection typically starts at the input of the first stage and progresses toward the output to isolate the faulty stage.
Question 5: An SCR in a power control circuit fails to trigger. Which component should be checked first?
- The anode load resistor
- The gate triggering circuit (Correct answer)
- The cathode bypass capacitor
- The DC power supply output
Correct answer: The gate triggering circuit
SCR triggering depends on gate current; a faulty gate circuit is the most common cause of failure to fire.
Question 6: What is the effect of an open bypass capacitor in an amplifier's emitter circuit?
- Increased voltage gain due to reduced feedback
- Reduced voltage gain due to increased AC emitter resistance (Correct answer)
- No change in gain
- Oscillation of the amplifier stage
Correct answer: Reduced voltage gain due to increased AC emitter resistance
An open bypass capacitor leaves the emitter resistor in the AC signal path, introducing negative feedback that reduces voltage gain.
Question 7: A full-wave bridge rectifier has one diode open. Which symptom will the output display?
- No output at all
- Pulsating DC at full frequency with normal amplitude
- Half-wave rectified output at reduced frequency (Correct answer)
- Full-wave output with increased ripple
Correct answer: Half-wave rectified output at reduced frequency
With one diode open in a bridge rectifier, only two of the four conduction paths work, resulting in half-wave rectification with half the normal repetition rate.
ISCET Component-Level Troubleshooting 3
A technician suspects a leaky electrolytic capacitor.
Which symptom best supports this diagnosis?