Fault Diagnosis, Testing and Repair Procedure
What this domain tests
Fault Diagnosis, Testing and Repair Procedure tests a systematic method from customer complaint to verified repair, including safety tests and documentation.
Core rules
- Follow a sequence: record the complaint, inspect for damage or burning, isolate and prove dead, verify the supply, then use half-split testing to narrow the fault. Do not replace parts at random.
- Test from the supply towards the load: plug, cord, switch, fuse/MCB, thermostat, component. Use voltage, continuity, resistance, insulation and earth-continuity tests as appropriate.
- Repair or replace with an identical-rated part. After repair, perform functional and safety tests: insulation resistance, earth continuity, polarity, current draw and operation under load.
- Record the complaint, tests, parts, labour and warranty on a job card. Explain the cause and the repair to the customer.
Worked example
A mixer-grinder trips the MCB when switched on. With the mixer unplugged, an insulation test between live/neutral and earth reads 0.2 MΩ. Reasoning: this is an insulation fault, not a supply fault. Inspect for water ingress, carbon brush dust and damaged wiring; clean and dry the motor, replace worn brushes, and retest. If insulation remains below 1 MΩ, replace the motor or declare the appliance unsafe.
Traps that cost marks
Fitting a new part without confirming the fault; testing only the appliance and not the socket circuit; skipping the post-repair insulation test; ignoring a damaged cord; and failing to document the repair.