Testing, Fault Diagnosis and Repair of Appliances
What the exam tests
This domain tests systematic fault finding in appliances: isolation, visual inspection, continuity, voltage, current, insulation resistance and repair verification.
Core rules
- Work in a sequence: isolate, inspect for damage, test the supply, test the cord and plug, then test the appliance. Divide the circuit at accessible points.
- A multimeter on ohms must be used only on a dead circuit. Continuity should read near zero ohms; an open circuit reads infinite.
- Insulation resistance is measured with a megger, typically at 500 V DC for 230 V appliances. A common pass value is at least 1 MΩ, but the manufacturer's figure governs. Disconnect electronics before megger testing.
- After repair, check that safety devices are present, ratings match, terminals are tight, earth continuity is good and insulation is satisfactory.
Worked example
A mixer is dead. The socket is live. The plug fuse is blown. Replace the fuse only after finding why: inspect the cord for a short, test the motor winding and check the switch. If the new fuse blows immediately, there is a short; do not keep replacing fuses.
Traps
Do not measure resistance on a live circuit. Do not megger a circuit containing sensitive electronics. Do not bypass a thermal cut-out or earth. Do not assume a blown fuse is the fault; it is a symptom. Do not return an appliance to service without an insulation test.