Electrical and Electronic Appliances: Repair and Maintenance
The Electrical and Electronic Appliances: Repair and Maintenance domain tests fault-finding in domestic appliances such as irons, mixers, fans, heaters, refrigerators and washing machines. The exam emphasises safe isolation, systematic testing and correct replacement ratings.
Core rules and concepts
- Isolate and lock off the supply before opening an appliance. Discharge large capacitors, especially in SMPS, inverters and motor drives; a charged capacitor can deliver a dangerous shock after unplugging.
- Use a multimeter for continuity and resistance, a clamp meter for current, and an insulation tester for leakage. Compare readings with the appliance rating plate.
- Common faults: blown fuse, broken cord, faulty switch, open thermostat/thermal fuse, open heating element, failed motor capacitor, worn brushes, blocked filter or door interlock.
- Replace parts with the same voltage, current, wattage and temperature rating. A higher-rated fuse does not protect the circuit.
- Test in a logical order: supply, cord, switch, protection device, load, then control circuit.
Worked example
A 1000 W, 230 V electric iron does not heat. The plug and cord test continuous; the thermostat is open when cold. The element resistance should be R = V²/P = 230²/1000 = 52.9 Ω. If the element reads open circuit, replace it. If it reads about 53 Ω, the element is likely good, so recheck the thermostat, thermal fuse and switch.
Traps that cost marks
Working on a live appliance; assuming the fuse is the only fault; fitting a fuse with a higher rating; not discharging capacitors; measuring resistance on a powered circuit; ignoring a faulty earth connection; replacing a thermostat without checking its temperature rating.