The machine is completely dead. What do I check first?
Start with safety and scope. Confirm incoming power, control power, E-stop/safety state, main protective devices, and whether the entire machine is dead or only one control section. Do not immediately open the PLC program.
The PLC output is on but the actuator does not move. What next?
Trace from output terminal to intermediate relays, field wiring, coil or valve, available energy, mechanical movement, and feedback. A software ON state proves only the logic command.
A fuse blew. Should I replace it?
Only after identifying the protected circuit and inspecting for a likely short or overload. Use the correct type and rating. A fuse is evidence that abnormal current occurred.
The same fault disappears after reset. Is it fixed?
No. A reset proves only that the system can recover. Capture fault history, identify trigger conditions, and verify whether the underlying cause remains.
Production wants me to bypass an interlock. What do I do?
Follow site safety procedures and your authorization. Do not defeat a safety or process protection simply because production is waiting. Escalate if there is pressure to work outside the approved method.
When should I connect to the PLC?
When the symptom suggests a logic, I/O, sequence, or communication issue and basic power/safety conditions are understood. Use the PLC to find missing conditions, not as the automatic first step for every fault.
How do I give an ETA when I do not know the cause?
Give a diagnostic status and next update point rather than inventing a repair time. Explain what is confirmed, what is being tested, and any known dependencies.
How do I know when to stop troubleshooting alone?
Escalate when safety or authorization is uncertain, the system requires specialized knowledge, repeated tests are not narrowing the fault, or delay creates more risk than the cost of bringing help.
What makes a good breakdown note?
Symptom, time, alarms, important measurements, cause, correction, configuration changes, verification, and follow-up action. Avoid vague notes such as “fixed wire.”
What should I verify before leaving?
Normal safety devices, no forces or bypasses, correct parameters, stable repeated operation, no abnormal current/temperature/noise, product quality where relevant, and a clear handover.