ISCET Component-Level Troubleshooting 4 — Questions and Answers
Question 1: A technician uses the half-splitting (divide and conquer) method. What is the primary advantage of this technique?
- It always starts at the power supply
- It minimizes the number of tests needed to isolate a fault (Correct answer)
- It eliminates the need for schematics
- It works only on digital circuits
Correct answer: It minimizes the number of tests needed to isolate a fault
Half-splitting divides the circuit at its midpoint each test, logarithmically reducing the number of checks needed to isolate a fault.
Question 2: Which failure mode of an electrolytic capacitor is indicated by visible bulging or electrolyte leakage?
- Open circuit failure
- Catastrophic failure due to overvoltage or reversed polarity (Correct answer)
- High ESR failure
- Dielectric absorption
Correct answer: Catastrophic failure due to overvoltage or reversed polarity
Bulging and leakage result from excessive internal pressure caused by overvoltage, reverse polarity installation, or thermal stress leading to catastrophic failure.
Question 3: When checking a transformer for a shorted winding, a technician should measure:
- Output AC voltage only
- Primary and secondary DC resistance and compare to specifications
- Insulation resistance between windings with a megohmmeter
- Both B and C (Correct answer)
Correct answer: Both B and C
Shorted windings reduce DC resistance below specification, and a megohmmeter check confirms inter-winding insulation integrity; both tests together give a complete picture.
Question 4: A PNP transistor has its emitter at +12 V, base at +11.3 V, and collector at +6 V. The transistor is:
- In cutoff
- In the active region (Correct answer)
- In saturation
- Oscillating
Correct answer: In the active region
VEB ≈ 0.7 V forward biases the emitter-base junction, and VEC = 6 V provides adequate collector voltage, placing it in the active region.
Question 5: What does high ESR (Equivalent Series Resistance) in an electrolytic capacitor cause in a switching power supply?
- Increased output voltage
- Excessive output ripple and overheating of the capacitor (Correct answer)
- Reduced switching frequency
- Lower inrush current
Correct answer: Excessive output ripple and overheating of the capacitor
High ESR prevents the capacitor from effectively filtering ripple, increasing output ripple voltage and generating heat within the capacitor.
Question 6: A technician measures 0 V at the output of a linear voltage regulator IC. The input voltage is correct. What should be checked next?
- The load resistance
- The adjust or enable pin and output capacitor (Correct answer)
- The transformer secondary winding
- The AC line fuse
Correct answer: The adjust or enable pin and output capacitor
With correct input voltage, a faulty adjust/enable pin or shorted output capacitor are the next most likely causes of zero output from a regulator IC.
Question 7: In a digital logic circuit, a gate output is stuck HIGH regardless of input combinations. Which fault is least likely?
- Output pin shorted to VCC
- Internal gate failure
- Faulty pull-up resistor holding output high
- Open output pin (Correct answer)
Correct answer: Open output pin
An open output pin would float or be pulled by external components rather than being stuck definitively HIGH; the other faults directly drive the output high.
ISCET Component-Level Troubleshooting 4
A technician uses the half-splitting (divide and conquer) method.
What is the primary advantage of this technique?