Maintenance, Troubleshooting and Fault Diagnosis
Maintenance, Troubleshooting and Fault Diagnosis
This domain tests maintenance strategy, reliability measures and structured fault-finding on mechatronics equipment. Expect a calculation of availability or OEE, a question on which maintenance type suits a symptom, and a logical sequence for diagnosing a fault.
Core rules
- Strategies: breakdown (run to failure), preventive (time or count based), predictive or condition-based (vibration analysis, thermography, oil analysis, ultrasound), and corrective after detection.
- MTBF = total operating time / number of failures; MTTR = total repair time / number of repairs. Availability = MTBF / (MTBF + MTTR).
- OEE = availability × performance × quality, using planned production time as the base. Availability = run time / planned time; performance = (ideal cycle time × total count) / run time; quality = good count / total count.
- Fault-finding sequence: gather symptoms and error codes, interview the operator, observe safely, isolate to a subsystem, test with a meter or PLC status, rectify the root cause, then verify and record.
- Root cause tools: 5 Whys, fishbone (man, machine, method, material, measurement, environment). Replacing parts without finding the cause repeats the failure.
Worked example
A line is planned for 480 min per shift. It stops for 48 min, produces 400 pieces at an ideal cycle of 1.0 min, and rejects 8 pieces. Availability = 432/480 = 0.90. Performance = (1.0 × 400)/432 = 0.926. Quality = 392/400 = 0.98. OEE = 0.90 × 0.926 × 0.98 = 0.817, about 82 %.
Traps
Using total calendar time instead of planned production time; mixing MTBF with MTTF; treating OEE as a pure availability figure; fixing the symptom without root cause analysis.