Diagnosis, Fault Finding and Troubleshooting
Diagnosis, Fault Finding and Troubleshooting is the disciplined process of turning a customer complaint into a verified defect. The exam rewards a repeatable sequence and evidence, not random part swapping.
A practical sequence
Start with the complaint and history: when did it start, after a drop, liquid, update or charger? Record model, IMEI and accessories. Inspect for cracks, corrosion, a swollen battery, burnt smell and bent pins. Then isolate power: use a known-good battery or current-limited supply and note standby and boot current. Check charging input, PMIC rails and power-key response. Only then move to software: safe mode, recovery, logs and recent updates. Compare with a known-good device or schematic where available.
Half-split and symptom mapping
Half-split testing divides the path into sections to locate the faulty block. A dead phone with no charging current points to input, protection or charging IC; a phone that boots but has no display points to display, backlight or connector; intermittent touch often points to a flex or connector rather than the SoC. Write down each measurement so the next technician can repeat it.
Worked example
A handset does not charge. The technician tries a known-good charger and cable, cleans the port, then measures voltage at the port and battery connector. If input voltage is present but the battery does not rise, the charging IC or battery is suspect. If no input voltage arrives, the port, flex or protection component is suspect. A software reset is not the first step because the symptom is electrical.
Traps
Do not replace the motherboard because a battery is flat. Do not trust a visual “looks fine” inspection. Do not skip the charger and cable check. Avoid diagnosing from a single voltage reading; confirm with current draw and a second measurement.