Top Yasnac & Yaskawa CNC Error Codes Explained & How To Fix

Yasnac and early Yaskawa CNC controls are still running on many older lathes and mills across automotive suppliers, job shops, and heavy machining plants. Controls like YASNAC MX1, MX2, MX3, J300, J50, J70 and early Yaskawa CNC ServoPack systems are stable but unforgiving. When an alarm appears, it usually points to a real electrical, mechanical, or feedback problem.

Alarm 401 - SERVO ERROR

What it means
The axis servo cannot follow the commanded position.

Common causes

• Ballscrew binding or axis crash damage
• Servo motor overload
• Encoder feedback instability
• Excessive acceleration or feedrate

How to fix

• Jog the axis at low speed and feel for resistance
• Inspect ballscrew, couplings, and lubrication
• Check servo motor load and temperature
• Reduce rapid and acceleration temporarily to test

Alarm 410 - OVERCURRENT

What it means
Servo amplifier detected excessive current draw.

Common causes

• Shorted motor cable
• Mechanical jam
• Failed power transistor in the drive

How to fix

• Power off and inspect motor and drive cables
• Check for axis blockage or collision damage
• If alarm triggers immediately on power-up, test amplifier and motor insulation

Alarm 414 - SERVO OVERLOAD

What it means
Servo motor load exceeded allowable limit for too long.

Common causes

• Heavy cutting load
• Worn thrust bearings
• Poor lubrication

How to fix

• Reduce cutting parameters
• Inspect lubrication system
• Check axis bearings and couplings for wear

Alarm 417 - ENCODER ERROR

What it means
The control lost valid position feedback from the encoder.

Common causes

• Loose encoder connector
• Encoder cable shielding damage
• Encoder power supply failure

How to fix

• Reseat encoder connectors at motor and drive
• Inspect cable for oil ingress or crushed shielding
• Measure encoder supply voltage at the motor

Alarm 421 - SERVO AMP FAULT

What it means
The servo amplifier reported an internal fault.

Common causes

• Overheating
• DC bus instability
• Aging components in the drive

How to fix

• Check cabinet cooling fans and filters
• Measure incoming line voltage and DC bus
• Swap amplifier with another axis for confirmation if possible

Alarm 510 - SPINDLE ALARM

What it means
Abnormal condition detected in the spindle drive.

Common causes

• Spindle overload during cutting
• Faulty spindle encoder
• Spindle drive power section fault

How to fix

• Reduce spindle load and test at low RPM
• Inspect spindle encoder and cables
• Review spindle drive diagnostics and LEDs

Alarm 520 - SPINDLE ORIENTATION ERROR

What it means
The spindle could not reach or hold the commanded orientation.

Common causes

• Orientation encoder failure
• Mechanical slip in belt or coupling
• Parameter drift after power loss

How to fix

• Check spindle orientation sensor and cabling
• Inspect belts and couplings for slippage
• Re-run spindle orientation setup if supported

Alarm 600 - EMERGENCY STOP ACTIVE

What it means
Emergency stop circuit is open.

Common causes

• E-stop button pressed
• Door or safety chain open
• Broken safety relay or wiring

How to fix

• Release all E-stop buttons
• Check door interlocks and safety relays
• Trace the E-stop circuit with electrical prints

Alarm 700 - PARAMETER WRITE ENABLE ON

What it means
Parameter write mode is active, blocking normal operation.

Common causes

• Service mode left enabled
• Battery-backed parameters edited

How to fix

• Disable parameter write enable
• Power cycle the control
• Verify no parameters were unintentionally changed

Alarm 900 - PROGRAM ERROR

What it means
NC program contains an illegal or unsupported command.

Common causes

• Syntax error
• Program created for a different Yasnac version

How to fix

• Edit the program line indicated by the alarm
• Compare with a known-good program format
• Adjust CAM post-processor for the correct control

Alarm 910 - MEMORY ERROR

What it means
Control detected a problem in CNC memory.

Common causes

• Low backup battery voltage
• Aging RAM modules
• Corrupted program data

How to fix

• Replace backup batteries immediately
• Reload programs from external backup
• If persistent, inspect memory boards

Alarm 920 - I/O COMMUNICATION ERROR

What it means
Loss of communication between CNC and I/O or PLC section.

Common causes

• Loose I/O rack connectors
• Power supply instability
• Failing I/O boards

How to fix

• Reseat I/O modules and ribbon cables
• Check I/O power supply voltages
• Inspect cabinet for vibration-related damage

PROG ERROR (NO ADDRESS)

What it means
A program block is missing a required address or word.

Common causes

• Incomplete block after editing
• Manual program entry error
• Post-processor mismatch

How to fix

• Move the cursor to the line indicated by the alarm
• Check that each block contains valid addresses G, X, Z, F etc.
• Compare with a known-good program format for the same control

PROG ERROR (UNUSABLE AXIS / CHANNEL)

What it means
The program calls an axis or channel that is not configured on the machine.

Common causes

• Program written for a different Yasnac model
• CAM post configured for more axes than available

How to fix

• Remove unsupported axis commands
• Correct the CAM post or manual code to match the machine configuration

PROG ERROR (G02 / G03)

What it means
Invalid circular interpolation command.

Common causes

• Missing I, J, or K values
• Invalid arc direction
• Zero-radius arc

How to fix

• Verify arc center values
• Check plane selection G17, G18, G19
• Replace with linear moves to isolate the error if needed

OVERFLOW (128 CH)

What it means
Program buffer or internal channel capacity exceeded.

Common causes

• Extremely long or complex program
• Excessive subroutine nesting
• Memory fragmentation on older controls

How to fix

• Split the program into smaller sections
• Reduce nested subroutine depth
• Power cycle the control to clear temporary buffers

RS232C ERROR

What it means
Serial communication error during program transfer.

Common causes

• Baud rate mismatch
• Incorrect parity or stop bit settings
• Poor cable quality or grounding

How to fix

• Match communication parameters on both sides
• Use a short, shielded cable
• Verify stable cabinet grounding

MIRROR IMAGE ERROR

What it means
Mirror image command used incorrectly or in an unsupported mode.

Common causes

• Mirror command active during canned cycle
• Unsupported axis mirror call

How to fix

• Cancel mirror mode before the affected block
• Verify mirror usage matches the control manual

MACRO / CALCULATION ERROR

What it means
Macro variable or calculation error detected.

Common causes

• Division by zero
• Undefined variable
• Invalid arithmetic expression

How to fix

• Review macro logic step by step
• Initialize all variables explicitly
• Simplify calculations to isolate the fault

MEMORY ERROR (RAM / ROM / CPU)

What it means
Internal memory or CPU self-check failed.

Common causes

• Low or dead backup batteries
• Aging memory modules
• Electrical noise or power instability

How to fix

• Replace backup batteries immediately
• Reload parameters and programs from backup
• Inspect cabinet power quality and grounding

TAPE MEMORY ERROR

What it means
Error reading from tape or tape memory system on older controls.

Common causes

• Corrupted tape data
• Tape reader hardware failure
• Dirty or worn read heads

How to fix

• Reload the program from a clean source
• Clean tape reader components if applicable
• Convert tape programs to internal memory where possible

Practical notes for legacy Yasnac systems

• Repeated servo alarms almost always trace back to mechanics or feedback, not software.
• Encoder cables and connectors are the most common failure point on 20+ year old machines.
• Battery maintenance is critical. Low battery causes random parameter and memory alarms.
• If one axis shows frequent faults, compare it electrically and mechanically to a healthy axis.

Yasnac and Yaskawa legacy controls are simple, deterministic, and honest. When an alarm appears, something real has changed in the machine.

About MDCplus

Our key features are real-time machine monitoring for swift issue resolution, power consumption tracking to promote sustainability, computerized maintenance management to reduce downtime, and vibration diagnostics for predictive maintenance. MDCplus's solutions are tailored for diverse industries, including aerospace, automotive, precision machining, and heavy industry. By delivering actionable insights and fostering seamless integration, we empower manufacturers to boost Overall Equipment Effectiveness (OEE), reduce operational costs, and achieve sustainable growth along with future planning.