Electrical and Mechanical Troubleshooting
What this domain tests
This domain tests systematic diagnosis: gathering information, using wiring diagrams, isolating the safety chain, interpreting drive fault codes, and distinguishing electrical from mechanical causes. It also tests meter selection and safe measurement practice.
Core method
- Gather evidence first: complaint, recent work, fault codes, and observed behavior. A fault code is a clue, not a diagnosis.
- Verify power and the safety chain: confirm voltage at the disconnect, then check the chain that includes door interlocks, gate switches, stop switches, pit switch, governor switch, slack-rope switch, buffer switches, and final limits.
- Half-split the circuit: measure from a known-good point toward the suspected open. Across an open contact you read the supply voltage; across a closed contact you read approximately zero.
- Use the right meter: correct CAT rating, correct function, and awareness of ghost voltage on high-impedance digital meters.
- Separate electrical from mechanical: excessive noise, vibration, or heat points to bearings, sheaves, guides, or alignment; intermittent faults after warm-up point to connections, coils, or drive components.
Worked example
A car stops between floors with no displayed fault. The doors are closed. Measure the safety chain at the controller: full voltage appears at the first test point but disappears after a particular hoistway door interlock. That voltage drop across the device identifies an open interlock, not a drive failure. Inspect the door lock roller and alignment, correct the gap, then re-test the chain and confirm the car runs. Replacing the drive would have been guesswork.
Traps that cost marks
- Jumpering or bypassing a safety device to "prove" a fault.
- Replacing parts before isolating the circuit.
- Using a meter outside its CAT rating or measuring resistance on a live circuit.
- Misreading ghost voltage as a real supply.
- Assuming the fault code names the failed component rather than the circuit affected.
Documentation
Record measurements, the failed device, and the correction. Repeat failures are usually found in the record, not in the machine room.