ISCET Component-Level Troubleshooting 5 — Questions and Answers
Question 1: A ceramic disc capacitor reads zero ohms on an ohmmeter. What does this indicate?
- The capacitor is functioning normally
- The capacitor is open
- The capacitor is shorted (Correct answer)
- The capacitor has high leakage
Correct answer: The capacitor is shorted
A zero-ohm reading on a non-electrolytic capacitor indicates a short circuit, as these capacitors should read very high or infinite resistance.
Question 2: Which in-circuit test method introduces a known-good signal at each stage to verify signal flow?
- Signal tracing
- Signal injection (Correct answer)
- Voltage substitution
- Component substitution
Correct answer: Signal injection
Signal injection introduces an external test signal at each stage input, allowing the technician to confirm signal flow forward through the circuit.
Question 3: A transistor amplifier has correct DC bias voltages but distorts the output signal. The most likely cause is:
- Open power supply filter capacitor
- Transistor operating outside its linear active region (Correct answer)
- Short-circuited bypass capacitor
- Incorrect supply voltage
Correct answer: Transistor operating outside its linear active region
If DC bias is correct but the output is distorted, the transistor is likely being driven into saturation or cutoff by the AC signal, indicating improper AC load line operation.
Question 4: What is the expected DMM reading across a good fuse in a powered circuit?
- Supply voltage
- 0 V (zero volts) (Correct answer)
- Infinite resistance
- Half the supply voltage
Correct answer: 0 V (zero volts)
A good fuse has very low resistance, so essentially no voltage drops across it in a powered circuit; a blown fuse would show full supply voltage.
Question 5: An inductor measures significantly lower resistance than specified. What fault is most likely?
- Open winding
- Shorted turns within the winding (Correct answer)
- Correct — inductors have low DC resistance
- Corroded terminal connections
Correct answer: Shorted turns within the winding
Shorted turns bypass portions of the winding, reducing the total DC resistance below its normal value.
Question 6: A technician is substituting components to isolate a fault. What is the main risk of this method?
- It may damage the replacement component if the root cause is not addressed (Correct answer)
- It requires expensive test equipment
- It only works on passive components
- It cannot identify intermittent faults
Correct answer: It may damage the replacement component if the root cause is not addressed
If the underlying fault (such as excessive voltage or current) is not found first, the replacement component may be damaged immediately upon installation.
Question 7: When measuring the forward voltage drop of an LED with a DMM on the diode test setting, the expected reading is approximately:
- 0.3 V
- 0.6–0.7 V
- 1.8–3.5 V depending on LED color (Correct answer)
- 12 V
Correct answer: 1.8–3.5 V depending on LED color
LEDs have higher forward voltage drops than silicon diodes, typically ranging from about 1.8 V for red LEDs to 3.5 V for blue/white LEDs.
ISCET Component-Level Troubleshooting 5
A ceramic disc capacitor reads zero ohms on an ohmmeter.
What does this indicate?