The Mitsubishi M800 series (M800S / M800W) is the high-end successor to the M700, paired with MDS-E / MDS-EH / MDS-EM drive units. As with the M70/M80, faults appear as NC alarms on the controller and drive (AL) alarms on the amplifier. Read both together for the fastest diagnosis.
How M800 Alarms Are Grouped
- EMG — Emergency stop (with a cause sub-code)
- S01 / S02 / S03 — Servo / drive system alarms
- Z70 / Z71 / Z73 — Absolute position (encoder) alarms & warnings
- M01 — Operation error (sub-code) • P-codes — Program errors
- AL (hex) — MDS-E/EH/EM servo & spindle drive alarms
Common NC Alarms
| Alarm | Meaning | Common Cause & Fix |
|---|---|---|
| EMG | Emergency stop active | Check the cause letters after EMG (PLC, EXIN, SRV, LINE). Release E-stop; check door/limit/PLC interlocks and the drive ready chain. |
| S01 | Servo alarm | A drive AL alarm is active — read the AL code on the MDS unit (table below) and act on it. |
| S02 | Initial parameter error | A servo parameter is out of range for the indicated axis. Check the servo setup parameters. |
| S03 | Drive communication / safety alarm | Check the optical comms cables between NC and drives and the ready signal. |
| Z70 | Absolute position illegal | ABS position lost (battery/board work). Re-establish the zero point. |
| Z71 | Absolute position detector alarm | Low detector battery or encoder fault. Replace battery; check encoder cable. |
| Z73 | ABS warning | Detector speed too high at power-on or weak battery — usually clears; replace battery if recurring. |
| M01 | Operation error | Interlock/condition not met. Read the M01 sub-code for the exact cause. |
MDS-E / EH / EM Drive Alarms (AL Codes)
| Code | Meaning | Common Cause & Fix |
|---|---|---|
| AL 10 | Insufficient (low) voltage | DC bus undervoltage — check input supply, contactor and power supply unit. |
| AL 20 | No signal — detector (encoder) | Feedback lost. Check encoder cable/connector; replace encoder if faulty. |
| AL 23 | Excessive speed error | Motor cannot follow command — overload, bind or feedback fault. |
| AL 24 | Ground fault | Motor or cable insulation breakdown. Megger the motor and cables. |
| AL 25 | Absolute position lost | Detector battery failed. Replace battery and redo ABS setup. |
| AL 30 | Over-regeneration | Regenerative resistor overloaded — fast cycles or resistor/circuit fault. |
| AL 31 | Overspeed | Motor exceeded limit — feedback or parameter fault. |
| AL 32 | Power module overcurrent | Short/ground in motor or failed power module. Test motor; repair/replace drive. |
| AL 33 | Overvoltage | DC bus over-voltage — regenerative fault or high input voltage. |
| AL 34 / AL 36 | NC–drive communication error | Optical comms fault. Check fibre-optic cables/connectors between NC and drives. |
| AL 37 | Initial parameter error | Drive parameter out of range. Check/restore servo or spindle parameters. |
| AL 3B | Power module overheat | Cooling fan failure or blocked heatsink. Clean and replace the drive fan. |
| AL 46 | Motor overheat | Overload or failed motor thermal sensor / cooling fan. |
| AL 50 | Overload | Continuous overload (thermal). Check cutting load, friction and balance. |
| AL 52 | Excessive error | Position error too large — bind, low gain, or drive/motor fault. |
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Quick-reference of common alarms. For the complete list, refer to the Mitsubishi M800/M80 Series Alarm/Parameter Manual.