Question 55 CEL02 - Chief Engineer - Limited (Alt)

The Correct Answer is B **Why option B is correct:** Troubleshooting PCB faults efficiently requires a logical, data-driven approach. Component substitution is a valid, though often last-resort, technique used to confirm a component failure. It is only practical and cost-effective when the faulty component has been reasonably isolated. This isolation is achieved primarily through: * **Visual Inspection:** Looking for obvious signs of damage (e.g., burn marks, cracked packages, bulging capacitors, cold solder joints). If a component is visually damaged, it becomes the primary suspect for substitution. * **Live Signal Tracing/Testing (Test Instruments):** Using oscilloscopes, logic analyzers, multimeters, etc., to verify that expected voltages, currents, and signals are present at the inputs and outputs of components. If a component receives the correct input but fails to produce the correct output, or if its operating parameters (like voltage drop or resistance) are out of specification, it is flagged as the suspect for substitution. Therefore, the substitution is based on evidence derived from inspection and testing, not random chance. **Why the other options are incorrect:** * **A) Methodical substitution of components starting at one end of the board and working towards the opposite end.** This is an extremely inefficient and costly "shotgun" approach. Substituting every component until the fault is found wastes significant time and resources and introduces a high risk of damaging the board or soldering new components incorrectly. Troubleshooting must be targeted. * **C) Component substitution is not recommended as a troubleshooting technique.** While it is often reserved as a technique of last resort (especially for surface-mount components), substitution remains a valid and necessary final step for confirming component failure, especially when in-circuit testing provides ambiguous results or when dealing with complex integrated circuits. It is a recommended part of the repair process, provided it is targeted. * **D) Random substitution of components in no particular pattern.** This is equivalent to option A but without even the pretense of a systematic process. Troubleshooting must always follow a logical, evidence-based process (diagnosis before replacement), making random substitution completely unacceptable.