How to Troubleshoot a Servo Drive Failure: Step-by-Step Tips for Fast Recovery

Servo drives are at the heart of precision manufacturing—controlling CNCs, robotics, packaging lines, and motion systems with speed and accuracy. But when one fails, productivity stalls fast.

Whether you're using a Mitsubishi MR-J2S, Yaskawa SGDH, or FANUC A06B series drive, quick and effective troubleshooting can make the difference between a minor delay and an extended shutdown.

This guide walks you through a proven, step-by-step troubleshooting process, highlights part-specific failure patterns, and explains when to repair, replace, or escalate the issue.

1. Identify the Symptoms: What Exactly Is Failing?

Start by gathering clear, observable symptoms. Don’t just note “drive fault”—be specific.

• Alarm or fault code on the drive display
• Unresponsive motor or jittering movement
• Unexpected stop during a motion cycle
• Burnt smell or overheated housing
• No display or power at all

🧠 Pro Tip: Jot down the drive’s model number, alarm code, and system behavior. This info is critical for isolating root causes and planning the next step.

2. Check the Obvious First: Power, Wiring, and Connectors

Before diving into fault codes or replacing parts, eliminate the simplest problems first. Many servo drive issues are caused by external factors rather than internal failures.

Basic Checks:

• Verify Power Input: Ensure the drive is receiving the correct input voltage. Use a multimeter to confirm power at the terminals.
• Inspect Cables and Terminals: Check for loose or corroded wiring. Look for arc marks or discolored terminals.
• Look for External Shorts or Ground Faults: A shorted motor or cable can trigger drive overcurrent or short circuit alarms.

💡 Example: On a Yaskawa SGDH drive, an A.C. alarm often points to a shorted output or incorrect wiring between the drive and motor.

✅ Tip: Grounding issues are a common root cause, especially in older systems like the Mitsubishi MR-J2S. Recheck shielded cables and ground straps after any equipment move or repair.

3. Interpret the Drive’s Alarm or Fault Code

Most servo drives are designed to self-diagnose, and your first real clue is often the alarm or fault code displayed on the front panel.

Common Codes by Brand:

Mitsubishi MR-J2S

• AL.37 – Overcurrent during deceleration
• AL.33 – Encoder error
• No Display – Possible power board failure or blown fuse

Yaskawa SGDH

• A.C – Output short circuit
• A.E – Overvoltage
• Solid Red LED – Internal hardware failure

FANUC A06B

• AL-1 – Overcurrent
• AL-3 – Regenerative error
• No LED – Indicates control or power board failure

📌 Tip: Some drives store a fault history log. Reviewing past errors can reveal patterns or environmental causes, like heat, vibration, or power fluctuations.

🧠 Tip from the Field: A recurring “A.C.” alarm on a Yaskawa SGDH turned out to be a frayed motor cable intermittently grounding against the frame. The drive wasn’t at fault—the wiring was.

4. Test the Motor – Or Try a Known-Good Unit

Servo drives and motors work as a system. A motor issue—such as a shorted coil or damaged encoder—can cause the drive to fault even if the drive itself is functioning properly.

• Swap in a Known-Good Motor: If available, this is the fastest method for isolating the issue.
• Perform a Megger or Resistance Test: Check for shorts to ground and confirm equal resistance across motor phases.

Brand-Specific Notes:

• MR-J2S: Encoder feedback issues are common—check cables and connectors.
• SGDH: Check for open motor windings if A.E or A.C alarms persist.
• A06B: Grounded motors are a top cause of drive damage and replacement.

🧰 Can’t test the motor on-site? We offer bench testing and joint evaluations for both drive and motor to help diagnose interaction issues before they escalate.

5. Decide: Repair, Replace, or Retest

✅ Repair the Drive If:

• The issue is clearly internal (e.g., blown capacitor, control board fault)
• The model is obsolete or expensive to replace
• You need a cost-effective fix and can wait a few days
• You want to retain the original settings and wiring

🛠 Industrial Automation Co. offers trusted repair service with up to a 2-year warranty on many models.

✅ Replace the Drive If:

• The same fault has occurred more than once
• There are visible signs of damage—burned components, cracked boards, etc.
• You need immediate recovery to avoid production delays
• You’re upgrading to newer models with better support

🔥 In Stock Now:
Mitsubishi MR-J2S-100B
Yaskawa SGDH-10DE
FANUC A06B-6079-H206

🔁 Retest or Escalate If:

• The fault is intermittent or only occurs under full load
• You’ve replaced multiple components but still experience faults
• You suspect issues like grounding, EMI, or environmental damage

📦 Good News: We offer free evaluations so you can make an informed repair-or-replace decision before committing.

Final Thoughts: Don’t Let a Servo Drive Failure Shut You Down

Troubleshooting a servo drive failure doesn’t have to be overwhelming. With a structured approach—checking power, wiring, fault codes, and motor condition—you can often isolate the issue and determine whether repair or replacement is the more prudent course of action.

At Industrial Automation Co., we help manufacturers minimize downtime by offering:

• ✅ Thousands of in-stock servo drives—including MR-J2S, SGDH, A06B, and more
• ✅ Trusted, warranty-backed repair services for legacy and current models
• ✅ Fast turnaround and same-day shipping on critical replacements

🛠 Need expert support or a quick replacement? Contact our team →

🔍 Browse our in-stock servo drives →