Troubleshooting, Maintenance and Safety
Troubleshooting, Maintenance and Safety tests a disciplined approach to faults and the safety rules that surround electrical work. The exam expects a logical fault-finding sequence, correct use of instruments, and recognition of hazards.
Core rules
- Follow a sequence: observe symptoms, form a hypothesis, test, isolate, repair, verify.
- Half-split: divide the signal path to locate the faulty block quickly; signal tracing follows the signal from input to output.
- Check power first: fuse, switch, supply rails, connectors. A blown fuse is a symptom, not the root cause.
- Isolate the load before measuring resistance; discharge capacitors before touching a power supply.
- Use a series lamp or isolation transformer for first power-up after repair.
- Safety: unplug and lock out, avoid working live, keep one hand in a pocket when live work is unavoidable, and use a CAT-rated meter.
- ESD: ground yourself and use anti-static bags for boards and ICs.
Worked example
A 9 V adapter-powered radio is dead and its fuse is blown. Replacing the fuse alone is unsafe because the fuse blew for a reason. Isolate the radio, measure the resistance across the supply input: a near-zero reading indicates a short, often a reversed electrolytic capacitor or a failed rectifier. Remove and test the suspect part, replace it, then power up through a series lamp. If the lamp glows brightly, a short remains; if it is dim, the repair is likely complete.
Traps
- Fitting a higher-rated fuse or a wire link; this removes protection and can cause fire.
- Measuring resistance on a live circuit; the ohmmeter can be damaged and the reading is meaningless.
- Assuming a dead board is safe; large capacitors can hold charge.
- Replacing parts without finding the cause, so the new part fails again.