CET Troubleshooting and Diagnostics 3 — Questions and Answers
Question 1: A half-wave rectifier produces a lower-than-expected DC output. Which component failure is most likely?
- The filter capacitor is shorted
- The diode has increased forward voltage drop (Correct answer)
- The transformer primary is open
- The load resistor is open
Correct answer: The diode has increased forward voltage drop
An increased diode forward voltage drop reduces the peak output voltage of the rectifier.
Question 2: When troubleshooting a logic circuit, a gate output is stuck HIGH regardless of inputs. This is called a:
- Stuck-at-0 fault
- Stuck-at-1 fault (Correct answer)
- Bridging fault
- Delay fault
Correct answer: Stuck-at-1 fault
A stuck-at-1 fault means the node is permanently logic HIGH regardless of normal switching inputs.
Question 3: An op-amp circuit has its output rail-to-rail with no input signal applied. The most likely cause is:
- Incorrect feedback resistor value
- Input offset voltage too large or feedback loop open (Correct answer)
- Output is correctly at mid-supply
- Power supply is too low
Correct answer: Input offset voltage too large or feedback loop open
A large input offset or open feedback loop causes the high open-loop gain to drive the output to saturation.
Question 4: During in-circuit testing, measuring resistance on a powered circuit gives unreliable results because:
- The ohmmeter battery is insufficient
- Parallel circuit paths affect the reading (Correct answer)
- AC components interfere with DC measurement
- The circuit ground floats
Correct answer: Parallel circuit paths affect the reading
Parallel paths in a circuit provide alternative current routes, making in-circuit resistance readings inaccurate.
Question 5: A voltage regulator IC output drops when load current increases. This symptom suggests:
- The regulator is working normally under load
- The regulator has insufficient input voltage headroom or is failing (Correct answer)
- The output capacitor is open
- The load is too light
Correct answer: The regulator has insufficient input voltage headroom or is failing
A linear regulator needs a minimum input-output differential (dropout voltage); insufficient headroom or a failing IC causes output sag under load.
Question 6: A technician uses the 'divide-and-conquer' troubleshooting method. This approach involves:
- Replacing all components one at a time from input to output
- Testing the midpoint of a signal chain to halve the suspected fault area (Correct answer)
- Dividing the schematic into sections and replacing whole sections
- Testing all power supply rails before signal tracing
Correct answer: Testing the midpoint of a signal chain to halve the suspected fault area
Divide-and-conquer splits the signal path at its midpoint, eliminating half the circuit from suspicion with each measurement.
Question 7: Intermittent faults in electronics are often caused by:
- Incorrect schematic values
- Cold solder joints or mechanical connection issues (Correct answer)
- Wrong component substitutions
- Inadequate power supply capacity
Correct answer: Cold solder joints or mechanical connection issues
Cold solder joints expand and contract with temperature, creating intermittent electrical contact.
CET Troubleshooting and Diagnostics 3
A half-wave rectifier produces a lower-than-expected DC output.
Which component failure is most likely?