The control throws Alarm 123 on a specific axis at power-on or during a rapid, halting motion and flagging the servo loop as faulty.
These are the failure paths we see most often on the Haas VF-2 for a alarm 123 axis servo condition. Likelihood reflects field frequency; First Check is what you can do remotely before sharing logs.
| Cause | Likelihood | First Check |
|---|---|---|
| Servo parameter mismatch after a drive or motor swap | High | Compare the axis servo parameters to the original machine build sheet |
| Encoder / feedback cable damaged or unseated at the servo | Medium | Inspect the feedback connector and cable routing for pinch or contamination |
| Drive fault or DC bus low from a supply issue | Medium | Read the drive alarm and the DC bus voltage on the power supply |
| Mechanical bind overloading the servo at speed | Low–Medium | Jog the axis slowly by hand with the servo off and feel for a hard stop |
Work through these in order. Each step is something you can perform and report back on without opening the enclosure or swapping parts.
Note which axis trips Alarm 123 and at what action — power-on, homing, or rapid. The trigger narrows it to parameter, feedback or load.
Open the alarm log and capture the sequence with timestamps. Repeated trips on one axis point to that axis's loop, not a shared supply.
Read the servo gain, following error and current-loop parameters for the faulted axis and compare to the build sheet. A wrong value after a swap is the common cause.
Inspect the encoder connector and read the drive's own alarm and DC bus voltage. A low bus or a drive fault reframes the problem away from the motor.
With the servo disabled, jog the axis by hand through its full travel. A hard spot that appears only under power suggests mechanical load, not electronics.
Alarm 123 is a servo-loop fault, and on the VF-2 it is most often a parameter or feedback issue rather than a dead drive. The alarm log and the per-axis parameter readout let us tell them apart. Cross-reference the broader collections: Servo / axis alarm · Servo & drive control.
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Usually not. We separate parameter, feedback and supply faults from a truly failed drive using the log and bus voltage, and only then suggest a swap.
You can acknowledge it, but if it returns on the same axis the root cause remains. We prefer to fix the parameter or feedback before resuming production.
The encoder cable is far more often the fault than the motor. We check the feedback path first and only implicate the motor after that tests clean.
Send the alarm log and the faulted-axis servo parameters. We tell you whether it is tuning, feedback or supply — before you order any hardware.
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When the symptom looks like a link or network fault instead.
A servo fault on a different platform with a similar remote path.
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