26.03.2025 by Viktor Siebert

“We’ve already replaced the servo drive, but the error remains.”
That’s how a customer approached us. His CNC machine was randomly shutting down two to three times a day with the error message: “Drive Overload.”

First Attempts – No Success

The customer started by replacing the servo module. No luck.
Then he changed the cables. Still nothing. External experts were called in – but of course, when they were onsite, the machine worked fine.

The motor looked good on the outside. He even replaced it temporarily with a motor borrowed from a neighbor. But the error kept coming back. So naturally, he thought:
“If the error still shows up with another motor, then it can’t be the motor.”

A Fresh Perspective

Eventually, the machine’s manufacturer recommended us.
With similar past experiences, our sales team suggested a thorough test of both the motor and the drive under real load conditions on our in-house test system.

From a pure measurement standpoint, everything looked okay. Nothing obviously wrong with the motor or the drive – although both showed signs of wear and had never been maintained.

But as always, our technicians didn’t stop there. They began a systematic fault analysis.

Recreating the Error in the Lab

Both devices ran flawlessly during the first hour of testing. But once external heat was applied, the motor started to jerk intermittently – as if it were briefly “losing its position.”

That was the clue.

The motor contains an encoder, a sensor system that sends feedback data to the drive. If this communication becomes unreliable, problems arise quickly.

We run all our test units through various conditions – cold, heat, vibration – to simulate real-world stress. This often reveals intermittent errors that only occur occasionally at the customer site.

The Real Culprit

After swapping in a different encoder, the motor ran smoothly – even under heat. But we wanted to be sure.

We mounted the suspicious encoder onto one of our own test motors – and the issue came back.

A closer inspection revealed:

1. A thin layer of dirt had built up on the encoder’s code disk
2. The encoder’s ball bearings were worn, causing minimal internal movement

These tiny imperfections were enough to affect the signal quality. At specific speeds and temperatures, the code disk would vibrate slightly, sending inaccurate data to the drive.

As the drive tried to compensate for the erratic feedback, it increased current output – until it hit its limit and showed “Drive Overload.”

The Takeaway

This case clearly shows:
🔍 The root cause of a problem isn’t always where the error message points.
Only a structured, in-depth diagnosis can reveal the true source of failure.

One Last Twist…

Believe it or not – the story didn’t end there.

Shortly after, the neighbor who lent the motor came to us… with the same error. No surprise: he had borrowed the very motor with the hidden defect.

We performed a full overhaul on the motor – replaced the encoder, refreshed the mechanical parts – and returned it in like-new condition.

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We specialize in Yaskawa motors and drives – from compact 5-watt units to powerful 45-kilowatt systems. With our in-depth testing and repair expertise, we bring even the trickiest cases back to life.

To the motor mentioned: Yaskawa SGMAH-04A1A6CD-OY AC Servo Motor
To the matching drive: Yaskawa Servopack SGDH-04AE-OY

#FaultDiagnosis #ServoDrive #Automation #Maintenance #ProblemSolving #IndustrialRepair #Yaskawa #CNC

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