FANUC SV1026 alarm usually means the servo axis assignment parameter is not set correctly. The most important item to check is parameter 1023. Make sure it does not contain negative values, duplicate values, or values larger than the number of controlled axes. After correcting the parameter, reinitialize the FSSB setting.
This alarm is commonly related to incorrect servo axis number assignment, parameter loss, wrong axis configuration, or an incomplete FSSB initialization after changing servo-related parameters.
What Does FANUC SV1026 Alarm Mean?
FANUC SV1026 means illegal axis assignment. The CNC system has detected that the servo axis assignment parameter is incorrect.
In practical troubleshooting, this alarm is usually caused by an incorrect setting of parameter 1023, which defines the servo axis number assignment for each controlled axis.
Main Alarm Information
| Alarm | FANUC SV1026 |
| Alarm Type | FSSB / Servo Axis Assignment Alarm |
| Alarm Meaning | Illegal axis assignment |
| Main Parameter to Check | Parameter 1023 |
| Main Related Area | Servo axis number setting, FSSB configuration, controlled axis assignment |
Common Causes of SV1026 Alarm
- Parameter 1023 is set incorrectly
- A negative value is set in parameter 1023
- Duplicate axis assignment values are used
- The setting value is larger than the number of controlled axes
- Servo axis number parameters are not matched with the actual machine axis configuration
- FSSB was not reinitialized after parameter correction
- Parameter loss or incorrect parameter restoration after CNC maintenance
Recommended Troubleshooting Order
- Check how many controlled axes the machine actually has.
- Check the setting values of parameter 1023 for each axis.
- Confirm that no negative value is set.
- Confirm that no duplicate value is assigned to different axes.
- Confirm that no value is larger than the number of controlled axes.
- Correct the wrong axis assignment values.
- Reinitialize the FSSB setting after correction.
- Power cycle the machine and check whether the alarm is cleared.
Step 1: Check Parameter 1023
The first step is to check parameter 1023 for all controlled axes. This parameter is used for servo axis number assignment.
If parameter 1023 is set incorrectly, the CNC system cannot correctly identify the servo axis assignment, and SV1026 alarm may occur.
Pay special attention to the following problems:
- Parameter 1023 contains a negative value
- Two or more axes use the same assignment value
- The parameter value is larger than the actual number of controlled axes
- The parameter setting does not match the machine axis configuration
Step 2: Check for Duplicate Axis Assignment
Each servo axis should have a correct and unique assignment according to the machine configuration. If two axes are assigned the same value, the system may detect an illegal axis assignment and generate SV1026.
For example, if the X axis and Z axis are both assigned the same servo axis number by mistake, the CNC system may not be able to map the FSSB axis correctly.
Step 3: Check Whether the Value Exceeds the Number of Controlled Axes
The setting value in parameter 1023 should not exceed the number of controlled axes on the machine.
For example, if the machine only has 3 controlled servo axes, but one axis is assigned a value larger than the controlled axis count, the system may treat this as an illegal assignment.
Step 4: Reinitialize FSSB After Correction
After correcting parameter 1023, reinitialize the FSSB setting. This step is important because the CNC system needs to rebuild the servo axis assignment based on the corrected parameter values.
If the parameter is corrected but FSSB is not reinitialized, the alarm may remain or the axis configuration may still not match the actual machine setting.
When Does SV1026 Commonly Appear?
- After CNC parameter loss
- After restoring parameters from an incorrect backup
- After replacing CNC control hardware
- After changing servo axis configuration
- After modifying FSSB-related parameters
- After adding, removing, or changing a controlled axis
SV1026 Diagnostic Table
| Finding | Possible Cause | Recommended Action |
| Parameter 1023 has a negative value | Invalid servo axis assignment | Correct the parameter value |
| Two axes have the same value in parameter 1023 | Duplicate axis assignment | Assign each axis correctly and uniquely |
| Parameter value is larger than the controlled axis count | Axis number exceeds machine configuration | Correct the setting according to the actual controlled axes |
| Alarm appears after parameter restoration | Wrong or incomplete parameter backup | Compare with the original parameter backup and correct 1023 |
| Parameter was corrected but alarm remains | FSSB not reinitialized | Reinitialize FSSB and power cycle the machine |
Important Notes Before Changing Parameters
Before changing parameter 1023 or any FSSB-related parameter, back up the current CNC parameters first. Incorrect servo parameter changes may cause new servo alarms, axis mismatch, or machine movement problems.
If the machine has special axis configuration, additional axes, gantry axis, loader axis, rotary axis, or customized ladder logic, confirm the original machine parameter backup before making changes.
Parts and Areas Related to SV1026 Alarm
- FANUC CNC system parameters
- Parameter 1023 servo axis assignment
- FSSB configuration
- Servo amplifier axis connection
- Controlled axis configuration
- Original machine parameter backup
Need Help with FANUC SV1026 Alarm?
REACO CNC provides technical support for FANUC FSSB-related servo alarms, CNC parameter checking, servo axis assignment issues, servo amplifier configuration, and FANUC CNC spare parts supply. If your machine shows SV1026 alarm, our team can help you review the axis assignment logic and identify whether the problem is caused by parameter 1023, FSSB initialization, parameter loss, or incorrect axis configuration.
You can contact REACO CNC and send us photos of the alarm screen, CNC system model, machine axis configuration, parameter 1023 values, FSSB setting screen, servo amplifier model, and any recent maintenance history. We can help confirm the likely cause and recommend suitable troubleshooting, repair, or replacement options for your FANUC CNC system.
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