A Hitachi Seiki HT-20 with a Yasnac LX2 control reaches the commanded X position on a G92 threading block, then waits without an alarm while the spindle continues to rotate. G76 and G32 produce the same result, but dry run completes. Because three threading methods fail at the synchronization point, diagnose their common spindle-synchronization path before changing cycle syntax or replacing more components.
Separate confirmed behavior from likely causes
| Evidence | Engineering conclusion |
|---|---|
| G92 reaches its programmed X position and then stops turret motion | The control executes positioning before waiting at the threading operation. |
| The spindle keeps rotating and no alarm appears | A running spindle alone does not prove that the control receives the synchronization information required for threading. |
| G92, G76, and G32 all behave the same way | The shared threading dependency is a stronger diagnostic target than one cycle's syntax. |
| The program runs in dry run mode | Basic axis movement is possible; the failure is associated with the normal threading conditions that dry run does not reproduce. |
| Replacing the encoder did not change the behavior | The original encoder is not established as the cause. Its wiring, interface, signal path, and related configuration remain unverified. |
| Parameters were corrupt and subsequently restored | An incorrect or incomplete restored setting is a credible hypothesis, but the evidence supplies no verified parameter numbers or values. |
Review the program without masking the common fault
The reported test uses G97 spindle mode at S800 with M03, then commands G92 at F.05. The available evidence does not establish that any of those values are invalid. Preserve the original program for comparison and avoid inventing replacement settings:
N3 T500
G97 S800 M03
G0 Z.5
T505 M08
X1.1
G92 X1. Z-1. F.05
X.990
X.980
X.970Because G76 and G32 stop in the same manner, changing only the G92 block is unlikely to isolate the fault. First determine what threading synchronization condition the LX2 is waiting for.
Diagnose the shared synchronization path
- Run the non-cutting test under controlled conditions and record the exact block and displayed X and Z positions where motion waits. Confirm that the spindle continues rotating and that no alarm or diagnostic message appears.
- Check the control's available spindle or threading diagnostics while the spindle runs. Determine whether spindle feedback changes and whether the threading synchronization or reference indication is detected. The evidence does not provide diagnostic addresses, so use the machine-specific documentation rather than guessed identifiers.
- Trace the feedback path from the replacement encoder through its connectors, wiring, interface hardware, and control input. Encoder replacement does not verify these remaining elements.
- Compare the restored parameter set with a known machine-specific backup or the exact HT-20/LX2 documentation. Concentrate on settings governing the spindle-feedback interface and threading option; do not load an unverified generic parameter list.
- After each correction, retest G32, G92, and G76 under the same safe setup. A valid repair should remove the common wait in normal operation, not merely allow dry-run motion.
Define a defensible repair result
Treat the issue as unresolved until normal-mode threading begins synchronized Z-axis motion and repeats consistently without an alarm. If diagnostics show no usable feedback despite spindle rotation, continue through the signal path. If feedback is present but the control still waits, prioritize validation of the restored configuration and threading-option settings. The evidence does not support a specific parameter value or prove a failed control board.
FAQ
Why does Yasnac LX2 stop on the G92 threading line without an alarm?
The control reaches the commanded X position but appears to wait for a threading condition. Since G76 and G32 also stop, check the common spindle-synchronization feedback and configuration path.
Why does threading work in dry run but not in normal operation?
Dry-run axis motion confirms that the turret can move, but it does not verify the normal threading synchronization path. Diagnose the spindle feedback indications under normal operating conditions.
Does replacing the spindle encoder rule out a feedback problem?
No. The unchanged symptom makes the original encoder less likely, but it does not verify the replacement encoder, connectors, wiring, interface hardware, control input, or restored parameters.