Got a Mitsubishi servo drive throwing random error codes at you? You’re not alone. Whether you’re new to factory automation or have been around the SMT block a few times, these servo alarm codes can feel like decoding alien language. But don’t worry — I’ve got you.
Quick Fix Table: Common Mitsubishi Servo Alarms
Here’s a handy table showing 3 of the most common Mitsubishi servo alarms I’ve seen, and how to fix them fast:
| Alarm Code | Meaning | Likely Cause | Fix |
|---|---|---|---|
| AL31.1 (A.31.1) | Motor Overspeed | 1. Pulse frequency too high 2. Short accel/decel time 3. Unstable system 4. Wrong gear ratio 5. Encoder failure | 1. Lower pulse frequency 2. Increase accel/decel time 3. Retune gain 4. Set correct gear ratio 5. Replace encoder or motor |
| ALE6/6.1 (A.E6) | Emergency Stop Triggered | 1. EMG–SG not connected 2. No 24V control power | 1. Reconnect EMG to SG at CN1 2. Supply 24V power |
| AL52 (A.52) | Excess Deviation Error | 1. Bad accel/decel settings 2. Torque limit too low 3. Power drop 4. Gain too low 5. External force 6. Mechanical jam 7. Encoder fault | Adjust time constant, torque limit, gain; check power and motor; replace encoder if needed |
Now let’s break it down for folks who want the full picture.
What Are Mitsubishi Servo Alarms?
Mitsubishi servo drives (like the MR-J2S, MR-J3, MR-ES) throw alarms when something goes off-script. The good news? These error codes are like a breadcrumb trail leading you to the real issue — if you know how to read them.
Most codes start with “AL” for alarms or “ALE” for warnings. You’ll see them flashing on the drive’s display, and they’re your drive’s way of waving a red flag.
Let’s explore the key ones that pop up in real-life production lines.
1. Motor Overspeed – AL31.1 (A.31.1)
- If your machine’s running too hot and fast, this one shows up.
Why it happens:
- You’re feeding it pulses like it’s a racecar — too fast.
- Your acceleration/deceleration time is too short.
- The system’s gain settings are unstable.
- Electronic gear ratio is off the charts.
- Or worst case: the encoder’s toasted.
How to fix it:
- Start by slowing down your input pulses.
- Lengthen those acceleration/deceleration curves.
- Retune the servo gain (sometimes factory default works fine).
- Recheck that gear ratio math.
- Swap out the encoder if you suspect damage.
Emergency Stop – ALE6 or ALE6.1
This is your servo’s panic button. It’ll freeze everything until the safety is cleared.
Why it happens:
- You didn’t wire the EMG and SG pins at CN1.
- There’s no 24V on the control loop.
How to fix it:
- Plug the EMG pin back into SG to close the safety loop.
- Make sure you’re supplying 24V power correctly.
This alarm looks scary, but it’s really just a wiring oops most of the time.
Position Error – AL52 (A.52)
This one’s a bit trickier — it means the servo couldn’t keep up with where it’s supposed to be.
What causes it?
- Your accel/decel time is too aggressive.
- Torque limits are choking the motor.
- Power supply is sagging.
- Gain is too low for the load.
- A heavy external force is spinning the shaft.
- Mechanical block or jam.
- Encoder isn’t doing its job.
What to do:
- Go easier on those motion curves.
- Raise the torque limit in the drive settings.
- Check voltage levels — if they’re dipping, swap to a stronger power supply.
- Tune up the gain until the motor follows smoothly.
- Reduce the load or upgrade to a higher torque motor.
- Fix any mechanical jams.
- Replace the encoder if it’s acting weird.
Other Useful Alarms to Know
Here’s a cheat sheet of other codes you might see on the MR-J2S series:
| Alarm Code | Meaning |
|---|---|
| AL10 (A.10) | Undervoltage |
| AL16 (A.16) | Encoder fault 1 |
| AL20 (A.20) | Encoder fault 2 |
| AL30 (A.30) | Regenerative braking error |
| AL37 (A.37) | Parameter error |
| AL50/51 (A.50/51) | Overload |
| ALE9 (A.E9) | Main circuit off |
How to Quickly Diagnose a Bad Motor
Here’s a down-to-earth trick:
Disconnect the motor wiring.
- Spin the shaft by hand.
- If it’s not smooth, the coil’s probably cooked.
- If you hear crunching from the encoder? It might be busted from a bad coupling or drop.
Final Thoughts: Keep Calm and Servo On
Honestly, Mitsubishi servo alarms can feel overwhelming at first. But once you know how to decode them, they’re actually helpful. They keep your system from blowing something up — literally.
If you’re stuck with a tricky error or unsure how to retune things, don’t hesitate to reach out. I’ve been helping SMT lines for years and I love solving weird equipment issues.
👉 Bookmark this page, or send it to your team. And if you’re dealing with rare equipment parts, like old Panasonic or Hitachi feeders, check out feedersmt.com. We stock the hard-to-find stuff and love saving your line from downtime.
