SYS_ALM129 Abnormal Power Supply (SERVO:AMPn) /LINEx
<Content> A power supply abnormality has been detected in the unit shown in parentheses.
<Action to Take> A drop in the input voltage to the corresponding unit has been detected. Check the power supply and power cables for abnormalities and determine whether the drop in input voltage was caused by a surge current or other factors.
SYS_ALM129 Abnormal Power Supply (SERVO:AMPn) /LINE1
129: A power supply abnormality was detected in the nth servo amplifier Cause of the malfunction: Focus on inspecting the amplifier’s power supply; check whether the 24V supply voltage is normal; check for external short circuits, etc.
24V Power Supply Failure In FANUC systems, the same fault cause may result in different alarm codes. For example, the 926 black screen alarm in older systems (OIB, OIC, 18I, etc.) has the same meaning and cause as the SYS_ALM129 alarm in newer systems (OID, OIF, 31I).
The ALM129 (926) FSSB alarm indicates a sudden fiber-optic break. Possible causes are:
1. The alarm occurs sporadically during X, Y, or Z-axis operation. This is typically caused by chafing of the feedback cable for that axis, resulting in a short circuit that triggers a sudden power loss to the driver and triggers the ALM129 (926) alarm. You can determine the cause by
repeatedly moving the axis or by replacing the feedback cable.
2. If a FANUC fully closed-loop encoder conversion box is connected downstream of the fiber optic cable, a short circuit in the external fully closed-loop cable or the read head can also cause sporadic 926 alarms. Move the axes repeatedly to determine which axis’s encoder is affected.
3. A sudden loss of power or excessively low voltage at the drive’s 24V input can also trigger the ALM129 (926) alarm. Check the power supply input or replace the power supply. (In some machine tools, a faulty external three-color indicator light or relay—which shares the 24V power supply with the driver—can also cause this issue.)
4. An unstable 24V switching power supply (low 24V output voltage; check with a multimeter) or one with high harmonic distortion may cause the fault. Therefore, replacing it directly with a new power supply is the quickest and most reliable solution.
5. A servo axis control card may be faulty; switch it to determine the cause.
