112600

Check encoder hardware connection and cable integrity at the spindle motor and NCK interface. Verify SSI cable shielding and termination if using absolute encoder feedback.

Power down the spindle drive before inspecting connectors.

Navigate to Diagnostics > Spindle > Encoder in the operator panel. Verify encoder signal presence and value updates in real-time. Check MD 37200 and MD 37201 match the physical encoder specification (incremental vs. absolute, PPR, bit resolution).

Perform spindle encoder reference run if applicable (MD 37240 - Encoder reference). Re-establish zero position synchronization between encoder and spindle drive controller.

If encoder values are missing, test with a scope at the encoder output and NCK input terminals. Replace encoder or interface cable if signal is absent.

Verify spindle drive configuration: Check MD 37100 (Spindle motor rated power), MD 37101 (Spindle motor rated speed), and MD 37102 (Spindle motor rated torque) match the physical spindle motor nameplate.

Navigate to Machine > Spindle in the NCK menu. Inspect MD 37105 (Spindle moment of inertia). If spindle load has changed (new chuck, gearbox), recalculate and update this parameter to prevent speed oscillation.

Check MD 37110 and MD 37111 PI controller gains. If gains are too low, the loop cannot track speed changes; if too high, oscillation triggers synchronization failure. Perform a ramp test: command slow speed ramp (100-500 RPM/sec) and observe encoder feedback tracking using Diagnostics > Spindle > Actual speed.

If tuning is suspect, perform auto-tuning routine (if available on your 840D model) or reduce proportional gain by 20%, then increase incrementally in 10% steps until synchronization holds stable.

Check NC program for explicit synchronization command (G96 - constant surface speed, or M19 - spindle orient). Verify that the program context expects synchronized operation.

Navigate to Machine > Spindle and verify MD 37240 (Spindle encoder reference run) is enabled (typically value 1 or 2). Check MD 37241 (Spindle synchronization speed threshold) - alarm 112600 only triggers if commanded speed exceeds this threshold. If threshold is 0, synchronization is disabled.

Increase spindle speed command above MD 37241 threshold and observe if encoder feedback (Diagnostics > Actual speed) tracks the setpoint within tolerance (typically ±2-5% on 840D classic systems).

If synchronization is not required for your application, disable it by setting MD 37240 = 0 or by removing synchronization logic from the NC program. If synchronization is required, lower MD 37241 threshold and retry with stable spindle drive tuning.