Resolving F07900 on SINAMICS S120 with Smart Line Module 6SL3130

Overview

A SINAMICS S120 drive line-up that uses a Smart Line Module (SLM) as its infeed instead of an Active Line Module (ALM) or Basic Line Module (BLM) requires a specific enable chain. When the control panel reports "Enabling the drive" but the Motor Module never transitions to the Operation state, and the Starter/Startdrive project topology omits the line module, the drive typically stalls waiting for the infeed operation signal (r863 / p864). The condition frequently surfaces as fault F07900 the moment a traversing command (JOG, setpoint, or motion job) is issued, even though commissioning diagnostics remain green.

This article documents the field-proven recovery path on a 6SL3120-2TE13-0ADx Double Motor Module driven by a 6SL3040-1MA01-0Axx Control Unit with a 6SL3130-6AE15-0AB1 (5 kW) Smart Line Module. The same root cause and remediation apply to any S120 drive object (DO) sourced from an SLM that is not declared in the topology.

Affected Components and Topology

The reference configuration uses the following catalog numbers:

The DRIVE-CLiQ topology is what Starter/Startdrive uses to identify each object. If the SLM is not powered and visible on DRIVE-CLiQ, the CU will mark it as topology violation and refuse to release downstream drive enables. Always verify the topology view (online → topology) shows the SLM as an active object, not as a placeholder or missing link.

Symptom Matrix

Root Cause: F07900 and the Infeed Operation Chain

Fault F07900 on SINAMICS S120 servo and vector drives is documented in the SINAMICS S120/S150 List Manual (LH1) as "Motor blocked or speed controller at end of stop". The drive evaluates the actual speed against the setpoint after the OFF1/OFF3 ramp; if the deviation persists beyond a monitoring window (p2161, p2163) the fault is latched. In a multi-axis S120 system, however, the most common root cause during commissioning is not a mechanical jam but a missing feedback path for the infeed:

• Bit r863.0 (infeed in operation) on every DO must be 1 before the drive releases its torque-producing enable (bit r899.0 / r5613.0).
• r863 is sourced via p864.1 (Control Unit) or p864 on the Motor Module, defaulting to the digital input on the line module or to the DO's own logic.
• When the SLM is excluded from the topology, or when its DQ interface is not used, the signal r722 (CU digital inputs) on the line module is not propagated. The DO therefore sees a permanent 0 on the infeed-run bit, and the enable chain hangs.

Field evidence in the reference case: r70 = 540 V confirmed that the DC link is fully precharged by the 6SL3130-6AE15-0AB1 SLM. r722.1 (DI1 of the CU320-2) was 0 because no 24 V was wired to the "infeed operation" terminal. Setting p864 = 1 on the Motor Module forces the infeed-run bit to TRUE without requiring an external DI, which immediately released the enable.

DRIVE-CLiQ Encoder Assignment (Secondary Cause)

F07900 also fires when the encoder physically wired to a motor reports stationary position feedback while the drive issues a torque-producing command. Verify the encoder assignment on every DRIVE-CLiQ port:

1. Open the topology in Starter (online) or Startdrive (TIA Portal).
2. Click each Motor Module and inspect ports X201, X202, X203 against the encoder connected at the motor.
3. If encoder for motor on X1 is plugged into the X2 port, the position counter will not increment → drive interprets as a stalled motor → F07900.
4. Re-seat the encoder cable to the correct port, or correct the topology assignment (drag the Sensor Module to the matching motor).

Refer to the SINAMICS S120 Commissioning Manual for the encoder-port-to-motor mapping convention.

Step-by-Step Resolution Procedure

Prerequisites

• Starter V18 / Startdrive V17 (TIA Portal V18) or later, with the S120 firmware support package (SSP) installed.
• Online connection to the CU320-2 via PROFIBUS, PROFINET, or Ethernet service port X127.
• 24 V control supply and three-phase line voltage applied to the 6SL3130-6AE15-0AB1 SLM.
• Drive objects commissioned to at least the motor ID and encoder type.

Procedure

1. Confirm the DC link. On the SLM drive object, read r70 (DC link voltage). For a 400 V class SLM, the value should rise from 0 to ≈ 540 V within 1 s of precharge. If r70 stays at 0, the line contactor is not closed or the SLM is faulted.
2. Verify the topology. In the online project tree, right-click the Control Unit → Topology. The SLM (DO type 11) must appear between the CU and the Motor Modules. If absent, run "Compare with offline" and accept the real topology.
3. Check digital input status. On the CU320-2, read r722 (DI status, bit-coded). Bit 0 = DI0, bit 1 = DI1, and so on. Identify which bit is mapped to p864 (default p864[0] = 722.1, i.e. DI1).
4. Force the infeed-run signal for commissioning. On the affected Motor Module, set p864 = 1 (signal source = TRUE). Save to RAM only; do not save to ROM until the permanent wiring is finalized.
5. Re-attempt the enable. From the control panel, click Enable. The status bar should complete within < 500 ms and the drive transitions to r899.0 = 1 (pulses enabled).
6. Run a JOG step. Issue a small JOG command (10 rpm, 1 s) on the drive object. If F07900 reappears, the cause is encoder wiring, not the infeed chain. Return to section "DRIVE-CLiQ Encoder Assignment".
7. Restore the production interlock. Wire a 24 V signal sourced from the line contactor (or a Safety output from a Smart Line Module with Safe Line Monitor) to the DI identified in step 3. Set p864 to the corresponding bit (e.g. p864 = 722.1) and verify the bit transitions correctly with the contactor.
8. Save and back up. Copy RAM to ROM on the CU, then perform a project upload to archive the final parameter set.

Parameter Reference

Verification and Commissioning Checks

After applying the fix, confirm the following signals on a STARTER trace or Startdrive trace:

• r863.0 = 1 within 50 ms of line contactor closure.
• r70 settles at ≈ 540 V (400 V class) and ripple is < 8 %.
• r722.1 = 1 (or the bit mapped in p864) when the infeed is commanded to run.
• No F07900 entry is added to the fault buffer during a 30-minute soak test at low speed (50 rpm).
• Alarm A7900 (warning threshold) is also absent, indicating a healthy feedback path.

For multi-axis systems, repeat the test on every drive object; one bad p864 assignment can stall the entire rack even when the SLM is healthy.

Related Fault Codes and Edge Cases

Edge case: if a 6SL3130-6AE15-0AB1 is replaced with a 6SL3130-6AE21-0AB1 (10 kW) or a Smart Line Module with a Safe Line Monitor, the DQ interface is required. In that configuration, do not set p864 = 1; instead, configure the safety telegram and wire the "infeed OK" status to a dedicated F-DI per SINAMICS S120 Safety Integrated Function Manual.

Topology and DRIVE-CLiQ Wiring Diagram

Field Notes and Lessons Learned

• Always declare the SLM in the offline topology. Starter/Startdrive will still auto-discover the SLM online, but if the offline project omits it, subsequent downloads overwrite the SLM configuration with defaults and the next power-up fails the enable chain.
• A 540 V reading on r70 is a strong "DC link ready" indicator; the issue lies upstream in the enable chain, not in the power section.
• F07900 should be treated as a symptom, not a root cause. The encoder, the infeed, the safety chain, and the mechanical system all converge on this fault code. Use the buffer timestamp to correlate with the moment a JOG or setpoint was issued.
• On a 2-DMM configuration where one motor is defective, isolate the bad drive object by setting p105 = 0 (motor data set changeover) on the affected DO, then verify the remaining three axes are independent and free of F07900.
• After every topology change, run an online/offline comparison and re-execute the drive commissioning wizard. Older firmware (≤ 5.1) on the CU320-2 sometimes retains stale DO references until a factory reset.