When a drive fails on an older machine, the conversation usually starts with price and availability. We think it should start somewhere else. A servo amplifier or an inverter seldom fails on its own; it fails because of where and how it runs. Replace it without asking why, and the replacement inherits the cause.
The failure is a symptom
Before the failed unit leaves the control cabinet, check what it lived with:
- the cabinet temperature and the state of its fans and filters;
- the motor and its cable, measured for insulation resistance;
- the brake resistor and its wiring, on axes that brake often;
- the mains supply: recent outages, voltage dips or work on the supply;
- the fault log in the drive or the controller, if it can still be read.
A drive that failed with an earth fault on a damaged motor cable will fail again on the same cable. A drive that overheated behind a blocked filter will overheat again. Neither problem is fixed by buying a better spare.
Save what you can before it leaves
A repair shop returns the hardware, not your settings. Before the unit goes anywhere, save the parameters to a file or to the control panel, write down the firmware version, and photograph the rating plate and the wiring. On CNC axes the servo settings live in the controller, so note which motor and amplifier the axis expects. These few minutes decide whether the returned unit runs the same afternoon or after days of tuning.
Three ways back
- Exchange unit. A refurbished unit of the same type, sent now, with your failed unit returned as a core. The fastest route when one is on a shelf.
- Repair and return. Your own unit, repaired and tested. Slower, but you get back the hardware revision and firmware the machine was commissioned with.
- Replacement. New, new surplus or used stock of the same type, or a successor. A successor means wiring, parameters and sometimes software, so it is a project, not a swap.
Our view: repair yours, keep one tested spare
For a drive family that is out of production, we would repair the failed unit and buy one tested spare of the same type, rather than run the machine on a used unit with no history. A used drive can be fine. It can also have spent years in a hot cabinet like yours. Refurbished, on Sparehawk, means inspected, cleaned and tested by the supplier; ask what the test was, and whether it ran a motor under load.
When the family still has years of support ahead, a new unit with the manufacturer’s warranty is often the simpler choice. When it has none, plan the move to its successor before the next failure picks the date for you. The obsolescence guide covers that plan.
What to ask a repairer
- What failed, and what was replaced?
- How was the unit tested: on a bench supply, or with a motor under load?
- What does the warranty cover, for how long, and does it start on dispatch or on installation?
- Do you return the failed parts or a report?
The same questions work for a refurbished unit bought outright. The guide to condition grades and the guide to warranty on surplus parts go further.