CET Troubleshooting and Diagnostics 2 — Questions and Answers
Question 1: A technician measures voltage across a resistor and gets 0V, but the source voltage is present. What is the most likely fault?
- The resistor is open
- The resistor is shorted (Correct answer)
- The supply voltage is too high
- The meter leads are reversed
Correct answer: The resistor is shorted
A shorted resistor allows all voltage to drop elsewhere, leaving 0V across it.
Question 2: When using an oscilloscope to troubleshoot, a waveform appears 'clipped' at the top. This most likely indicates:
- Insufficient input signal
- Amplifier saturation or clipping (Correct answer)
- Incorrect trigger setting
- Probe ground fault
Correct answer: Amplifier saturation or clipping
Flat tops on a waveform indicate the amplifier is driven into saturation, clipping the output.
Question 3: A capacitor in a filter circuit is suspected faulty. Which test best confirms an electrolytic capacitor has dried out?
- DC resistance check with ohmmeter
- ESR (Equivalent Series Resistance) measurement (Correct answer)
- Continuity test
- AC voltage reading across it
Correct answer: ESR (Equivalent Series Resistance) measurement
ESR measurement directly reveals increased internal resistance caused by electrolyte drying.
Question 4: In a transistor circuit, collector-to-emitter voltage equals the supply voltage. This indicates:
- The transistor is saturated
- The transistor is in active region
- The transistor is cut off (open) (Correct answer)
- The base drive is excessive
Correct answer: The transistor is cut off (open)
When VCE equals supply voltage, no current flows through the collector, meaning the transistor is cut off.
Question 5: A technician finds a circuit board with a burned resistor. After replacing it, the resistor burns again. What should be done next?
- Replace it with a higher wattage resistor and close the case
- Check the circuit for the root cause of excessive current (Correct answer)
- Replace the power supply
- Replace all nearby components
Correct answer: Check the circuit for the root cause of excessive current
A recurring burned resistor indicates an underlying fault causing overcurrent that must be identified and corrected.
Question 6: When troubleshooting an AM receiver with no audio output but normal AGC voltage, the fault is most likely in:
- The RF amplifier stage
- The antenna circuit
- The audio amplifier stage (Correct answer)
- The power supply
Correct answer: The audio amplifier stage
Normal AGC voltage indicates the RF and IF stages are functioning, pointing the fault to the audio section.
Question 7: A digital multimeter displays 'OL' when measuring resistance. What does this indicate?
- The component has zero resistance
- The resistance exceeds the selected range or the component is open (Correct answer)
- The battery is low
- The leads are reversed
Correct answer: The resistance exceeds the selected range or the component is open
OL (overload) means the reading exceeds the meter's selected range, or the circuit is open.
CET Troubleshooting and Diagnostics 2
A technician measures voltage across a resistor and gets 0V, but the source voltage is present.
What is the most likely fault?