What the SEG-4 alarm means

On CS8/CS8C the controller front 7-segment display shows '4': the amplifier drive-enable (DF) contact on J112 is open — the power stage refuses to enable one or more drives. We see this alarm constantly when servicing Staubli CS8 / CS9 (VAL3) systems, and the first on-site pass usually pins down the cause.

Most common causes

  • E-stop chain or guard interlock holding the DF loop open
  • Drive fault on one axis latching the DF contact open
  • Wiring fault between drives and RSI
  • STARC board fault
Field note: Based on our handling experience the first cause is the most frequent — use it as your starting point.

Step-by-step field fix

  1. Open Control Panel > Controller Status on the pendant to read which drive is flagged
  2. Check the event history for the amplifier number and the detailed fault
  3. Verify the E-stop chain and all guard interlocks are closed
  4. Check wiring between the drives and the RSI board
  5. If no individual drive is faulty, test the STARC board before swapping drives
Safety first: For Staubli seg-4, this alarm family involves the DC bus, which sits at several hundred volts and stays charged for minutes after power-off - touching terminals is a shock hazard. The self-serviceable action is Open Control Panel > Controller Status on the pendant to read which drive is flagged; anything past that falls under the DC bus and power stage and needs a certified engineer. On Staubli seg-4: checking incoming voltage at the disconnect and looking at breakers and fuses is fine to do yourself; opening the cabinet to touch bus terminals or pulling power modules needs a qualified electrician.

How we diagnose drive alarms on site

Staubli seg-4 belongs to the drive & power stage family. On Staubli seg-4 the failing stage is drive modules plus the 24 V external supply circuit (24VEXT alarms point there) on the CS8 / CS9 - the fault sits on the energy chain: mains input, rectification, DC bus, braking resistor, inverter power devices and the drive board. We start reading Staubli seg-4 at the pendant error list and VAL3 log, with cabinet module indicators.

The chain involved in Staubli seg-4 runs: three-phase mains -> rectifier -> DC bus (bus capacitors) -> brake chopper / braking resistor -> inverter (IGBT) -> motor.

Bottom line up front: E-stop chain or guard interlock holding the DF loop open is the first suspect for Staubli seg-4, but read it along the energy chain: Any link on this chain dropping voltage shows up at the end as a drive alarm, so order matters. We measure the mains first: more than 3% phase imbalance is enough to sag the bus under load, and plenty of bus over/under-voltage alarms are actually a grid problem wearing a robot costume. Mains fine, then the bus capacitors - bulged cases, weeping electrolyte or a lifted vent mean replacement; capacitance down 20% or more cannot hold the bus during braking. Last, the braking resistor: healthy values sit in the tens of ohms depending on rating, and an open or drifted resistor trips regenerative overvoltage directly.

Field notes on this page cover Staubli seg-4 (Amplifier Fault — DF Contactor Open (7-Segment Code 4)); written by the Henghuan repair team, updated 2026-10-01.

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Related Drive & Power Stage alarms

DCBusUV — DC Bus Undervoltage at Power-Up (Pre-charge Failure) 24VExt — External 24V Supply Fault (Safety System Dropout) OverTemp — Drive / Cabinet Overtemperature
Same family: this code belongs to the Drive & power stage alarms family - the page collects all Drive & power stage-family codes we have handled, with the common inspection order and spares.
Other brands: we also keep field-fix libraries for Epson · Nachi · Omron and more — see the complete alarm code hub.

Frequently asked questions

QWhat does the Staubli seg-4 alarm mean?

On CS8/CS8C the controller front 7-segment display shows '4': the amplifier drive-enable (DF) contact on J112 is open — the power stage refuses to enable one or more drives. We see this alarm constantly when servicing Staubli CS8 / CS9 (VAL3) systems, and the first on-site pass usually pins down the cause. Staubli seg-4 sits in the drive & power stage family; on our work orders the highest-frequency trigger for this code is "E-stop chain or guard interlock holding the DF loop open".

QCan I clear a Staubli seg-4 alarm myself?

Whether Staubli seg-4 clears on its own depends on the outcome of "Open Control Panel > Controller Status on the pendant to read which drive is flagged". Finish the flow with "If no individual drive is faulty, test the STARC board before swapping drives" to confirm Staubli seg-4 - do not skip it. If that step is clean, the second most frequent cause on Staubli seg-4 is "Drive fault on one axis latching the DF contact open". Do not chase takt through a repeating Staubli seg-4. Left alone, drive & power stage faults tend to graduate from repairable to must-replace.

QFor drive/power alarms like Staubli seg-4, what spares do you bring on site?

The commonest causes we see on Staubli seg-4 are "E-stop chain or guard interlock holding the DF loop open, Drive fault on one axis latching the DF contact open, Wiring fault between drives and RSI", so we stock the van against those. For Staubli seg-4 specifically, we stock the van along the energy chain: braking resistors, bus capacitors, input fuses, drive-board supply parts and the common power modules for the brand. For Staubli seg-4, drive alarms usually stop the whole line, so they sit at the front of our dispatch queue. Before we roll, tell us what Staubli seg-4 shows on the pendant error list and VAL3 log, with cabinet module indicators and what the machine was doing - phone or video triage is free.

The content on Staubli seg-4 was written by Henghuan Robotics service engineers from hands-on repair experience. Alarm descriptions are our own reference summary and may differ by controller or software version — defer to Staubli documentation, or contact us to confirm. Henghuan is an independent service provider with no affiliation or endorsement by Staubli.