What the 26108 alarm means

The intermediate-circuit voltage dropped below the limit — the drive is not getting enough supply to hold the axis. We have built up many handled cases of this KUKA KRC2 / KRC4 / KRC5 (KSS) alarm, and usually the first on-site inspection tells us what is wrong.

Most common causes

  • Incoming three-phase supply dip or missing phase
  • Faulty KSP input stage
  • Loose power cabling
  • Undersized cell supply during peak current
Field note: Confirm or rule out the first cause first — it is the situation we encounter most.

Step-by-step field fix

  1. Measure the incoming three-phase voltage at the cabinet
  2. Check fuses and phase monitoring
  3. Tighten power connections at the KSP
  4. Check for cell-wide voltage dips at cycle start; replace the KSP if the input stage is faulty
Safety first: For KUKA 26108, 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. On site you may not carry out the first step yourself: Measure the incoming three-phase voltage at the cabinet. Beyond that it is the DC bus and power stage work - leave it to a professional. On KUKA 26108: 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

KUKA 26108 belongs to the drive & power stage family. On KUKA 26108 the failing stage is KPP power packs and KSP servo packs (next-generation drive modules on KRC5) on the KRC2 / KRC4 / KRC5 - the fault sits on the energy chain: mains input, rectification, DC bus, braking resistor, inverter power devices and the drive board. We start reading KUKA 26108 at the smartPAD message window (KSS message numbers: 1xxx operator, 2xxxx drive) with KPP/KSP module LEDs.

The chain involved in KUKA 26108 runs: three-phase mains -> rectifier -> DC bus (bus capacitors) -> brake chopper / braking resistor -> inverter (IGBT) -> motor.

Bottom line up front: Incoming three-phase supply dip or missing phase is the first suspect for KUKA 26108, 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 KUKA 26108 (KSP DC Link Undervoltage (Axis N)); written by the Henghuan repair team, updated 2026-10-01.

Can't clear it yourself? Contact us for remote diagnosis

Tell us the alarm code, the model and what the machine was doing when the alarm appeared. KUKA 26108 is an everyday diagnosis for our engineers, and remote diagnosis (phone or video) costs nothing.

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Related Drive & Power Stage alarms

12005 — Ballast Resistor Temperature Sensor — Wire Disconnection 26012 — General Servo Error (Drive N) 26013 — General Inverter Failure (Drive N) 26107 — KSP DC Link Overvoltage (Axis N) 26111 — KSP Device Overtemperature (Axis N) 26122 — KSP Braking Resistor Fault (Axis N)
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 ABB · Yaskawa · Universal Robots and more — see the complete alarm code hub.

Frequently asked questions

QWhat does the KUKA 26108 alarm mean?

The intermediate-circuit voltage dropped below the limit — the drive is not getting enough supply to hold the axis. We have built up many handled cases of this KUKA KRC2 / KRC4 / KRC5 (KSS) alarm, and usually the first on-site inspection tells us what is wrong. KUKA 26108 sits in the drive & power stage family; on our work orders the highest-frequency trigger for this code is "Incoming three-phase supply dip or missing phase".

QCan I clear a KUKA 26108 alarm myself?

Whether KUKA 26108 clears on its own depends on the outcome of "Measure the incoming three-phase voltage at the cabinet". Finish the flow with "Check for cell-wide voltage dips at cycle start; replace the KSP if the input stage is faulty" to confirm KUKA 26108 - do not skip it. If that step is clean, the second most frequent cause on KUKA 26108 is "Faulty KSP input stage". Do not chase takt through a repeating KUKA 26108. Left alone, drive & power stage faults tend to graduate from repairable to must-replace.

QFor drive/power alarms like KUKA 26108, what spares do you bring on site?

The commonest causes we see on KUKA 26108 are "Incoming three-phase supply dip or missing phase, Faulty KSP input stage, Loose power cabling", so we stock the van against those. For KUKA 26108 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 KUKA 26108, drive alarms usually stop the whole line, so they sit at the front of our dispatch queue. Before we roll, tell us what KUKA 26108 shows on the smartPAD message window (KSS message numbers: 1xxx operator, 2xxxx drive) with KPP/KSP module LEDs and what the machine was doing - phone or video triage is free.

The content on KUKA 26108 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 KUKA documentation, or contact us to confirm. Henghuan is an independent service provider with no affiliation or endorsement by KUKA.