Alarm 1209 appears on a REALMECA RT-1SP lathe with a Fagor 8055T control when the X axis is commanded after startup. The X and Z axes complete the machine-reference movement, but the X-axis servo then displays “C.” The evidence identifies a velocity-following fault; it does not establish whether “C” is a separate drive code or merely the drive's alarm-state indication.
What Fagor 8055T Alarm 1209 Means
After the delay configured by axis parameter FBALTIME(P12), the control detects that actual axis velocity is below 50% or above 200% of programmed velocity. This comparison explains why an axis may move during referencing yet still alarm afterward: visible motion does not prove that commanded and measured velocities remain within the permitted relationship.
| Observed or documented item | Engineering significance |
|---|---|
| Alarm 1209, X-axis servo error | The CNC detected the documented velocity mismatch on the X axis. |
| X and Z complete reference movements | Basic motion is present; the failure occurs during or immediately after the reference sequence. |
| “C” appears only on the X servo | Use the X drive as the comparison target, but do not assume “C” and CNC alarm 1209 have identical meanings without the drive documentation. |
| Z axis operates without the reported fault | The Z channel provides a working in-machine comparison for commands, feedback behavior, and enable state. |
Control Response to the Fault
The documented response stops axis feed and spindle rotation, removes enable signals, cancels the CNC analog outputs, stops execution of the active part program, and activates the external emergency-stop output. If the fault is detected from the position loop, the control opens that loop and sets LOPEN to 1.
Because the control deliberately removes motion commands and enables after detection, measurements taken only after the alarm may reflect the shutdown response rather than the initiating condition. Capture the X-axis command and feedback behavior during referencing and at the instant the alarm appears.
Diagnostic Decision Path
- Repeat the startup and machine-reference sequence while recording exactly when the X drive changes to “C”: during X travel, when X stops, or after the CNC declares the axes referenced.
- Compare programmed and actual X-axis velocity during that interval. Alarm 1209 requires the measured value, after FBALTIME(P12), to fall outside the 50% to 200% window relative to the programmed value.
- Compare the same observable command, feedback, and enable transitions with the working Z axis. Use the comparison to separate an X-channel problem from a machine-wide control sequence problem.
- Inspect the configured X-axis FBALTIME(P12) value and related X-axis configuration, but preserve the current settings before making changes. The evidence identifies this parameter as the evaluation delay; it does not prove that its value is incorrect.
- Obtain the exact X-servo model documentation and decode the displayed “C.” Do not replace hardware or treat “C” as a confirmed component failure until its manufacturer-defined meaning is known.
Verification After Correction
Run the complete machine-reference sequence and confirm that X and Z both reach their reference positions without alarm 1209, the X servo does not enter the “C” state, and subsequent X motion works from both the handwheel and a cycle. Also confirm that axis enables remain active and that LOPEN is not set by another position-loop detection.
FAQ
What causes Fagor 8055T alarm 1209 on the X axis?
After FBALTIME(P12) expires, actual X-axis velocity is detected below 50% or above 200% of programmed velocity. The evidence does not identify which device or configuration causes that mismatch.
Why can the X axis home successfully and then show alarm 1209?
The axis can physically move while its measured velocity still violates the permitted relationship after the configured delay. Record command and feedback through the end of the reference cycle instead of treating successful movement as proof that the loop is healthy.
Does “C” on the X-axis servo identify the failed component?
Not from the available evidence. Decode “C” using documentation for the exact servo model and correlate its timing with CNC alarm 1209 before changing parameters or replacing hardware.