Mitsubishi M70 and M80 CNC systems show two main kinds of alarm: NC alarms on the controller screen, and drive (AL) alarms from the MDS servo/spindle amplifiers. Reading them together is the quickest route to diagnosis. Below are the codes technicians meet most often, with causes and fixes.
How Mitsubishi M70 / M80 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 (with sub-code)
- P-codes — Program errors
- AL (hex) — MDS servo/spindle drive amplifier alarms (shown on the drive 7-seg display)
Common NC Alarms
| Alarm | Meaning | Common Cause & Fix |
|---|---|---|
| EMG | Emergency stop active | Check the cause letters after EMG (e.g. PLC, EXIN, SRV, LINE). Release E-stop, check the 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 amplifier (see table below) and act on that. |
| S02 | Initial parameter error | A servo parameter is out of range. Check the servo setup parameters for the indicated axis. |
| S03 | Safety / drive communication alarm | Check the optical communication cables between NC and drives, and the drive ready signal. |
| Z70 | Absolute position illegal | ABS position lost (battery change/board work). Re-establish the zero point (absolute position setup). |
| Z71 | Absolute position detector alarm | Low detector battery or encoder fault. Replace the battery and check the encoder cable. |
| Z73 | ABS warning | Detector speed too high at power on, or weak battery — usually clears after a correct power-up; replace battery if recurring. |
| M01 | Operation error | Interlock/condition not met (e.g. axis not at reference, mode mismatch). Read the M01 sub-code for the exact cause. |
MDS Servo & Spindle Drive Alarms (AL Codes)
These appear on the MDS-D/DH, MDS-DM, MDS-E/EH amplifier display and as an S01 on the NC.
| Code | Meaning | Common Cause & Fix |
|---|---|---|
| AL 10 | Insufficient (low) voltage | DC bus undervoltage — check input supply, contactor and power supply unit. |
| AL 17 | A/D converter error | Drive internal fault. Power cycle; if it persists, repair/replace the amplifier. |
| AL 20 | No signal — detector (encoder) | Feedback signal lost. Check the encoder cable/connector; replace the encoder if faulty. |
| AL 23 | Excessive speed error | Motor cannot follow command — overload, mechanical bind, or feedback fault. |
| AL 24 | Ground fault | Motor or cable insulation breakdown. Megger the motor and power cables. |
| AL 25 | Absolute position lost | Detector battery failed. Replace battery and redo absolute position setup. |
| AL 30 | Over-regeneration | Regenerative resistor overloaded — rapid cycle times 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 (CRC / timeout) | Optical comms fault. Check the fibre-optic cables and connectors between NC and drives. |
| AL 37 | Initial parameter error | Drive parameter out of range. Check/restore the servo or spindle parameters. |
| AL 3A | Overcurrent (instantaneous) | Sudden overcurrent — motor short or power-stage fault. |
| 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 / motor 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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This is a quick-reference of commonly encountered alarms. For the complete official code list, always refer to the Mitsubishi M70/M80 Series Alarm/Parameter Manual.