Before the visit, note the machine brand, model, serial number, controller type and the exact sequence that causes the fault. Save alarm codes and take a short video if the problem is intermittent.
Keep the work area safe and accessible. Ensure the machine can be powered under the normal site safety procedure, and identify any recent changes to tooling, software, parameters or electrical supply.
If parts have already been replaced, list them. This prevents repeated troubleshooting and gives the technician a more complete picture of the machine history.