What the SRVO-043 alarm means

Regenerative energy from decelerating axes exceeded what the discharge circuit could absorb. The DC link voltage rose too high and the amplifier shut down to protect itself. We see this alarm constantly when servicing FANUC R-30iA / R-30iB / R-30iB Plus systems, and the first on-site pass usually pins down the cause.

Most common causes

  • Frequent high-speed deceleration with heavy load (cycle too aggressive)
  • Discharge resistor failure or its fan stopped
  • Regenerative discharge unit fault
  • Input power voltage too high
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. Reduce acceleration/deceleration or speed on the offending moves and see if the alarm stops
  2. Check the discharge resistor and its cooling fan on the amplifier
  3. Measure incoming 3-phase voltage (should be within spec)
  4. On systems with an external regenerative unit, check its alarm LEDs
Safety first: For FANUC srvo-043, servo circuits are live and motor shafts and reducers rotate: measuring current waveforms or winding resistance means contact with live or moving parts. On site you may look at after confirming power-off the first step yourself: Reduce acceleration/deceleration or speed on the offending moves and see if the alarm stops. Beyond that it is live servo circuits and rotating parts work - leave it to a professional.

How we diagnose servo alarms on site

FANUC srvo-043 belongs to the servo & drive family. On FANUC srvo-043 the failing stage is alpha-i / beta-i servo amplifiers with PSM supply modules and SVM servo modules (SPM where spindles fit) on the R-30iB Plus / R-30iB Mate Plus / R-30iA - the servo closed loop: current/velocity/position loop misbehaviour, motor-drive matching and load identification. We start reading FANUC srvo-043 at the iPendant ALARM screen (SRVO / MOTN / SYST / INTF prefixes) together with the amplifier's 7-segment status code.

The chain involved in FANUC srvo-043 runs: target -> position loop -> velocity loop -> current loop -> power output -> motor -> feedback -> loop compare.

FANUC srvo-043 can be a parameter problem, not hardware: Some servo alarms are parameters, not hardware: after a fixture change the load moved but gains and load identification were never redone, loop response degraded, and high speed or hard stops now raise following error or oscillation. The fix is updating tooling weight and centre-of-gravity data, re-running load identification and trimming gains to the real takt. No spares at all - but no drive swap will fix it either if the parameters stay stale.

Field notes on this page cover FANUC srvo-043 (DCAL Alarm - Discharge Alarm); written by the Henghuan repair team, updated 2026-10-01.

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Related Servo & Drive alarms

SRVO-021 — SRDY Off (Group / Axis) SRVO-023 — Stop Error Excess (Group / Axis) SRVO-024 — Move Error Excess (Group / Axis) SRVO-044 — HVAL Alarm - High Voltage SRVO-045 — HCAL Alarm - High Current SRVO-046 — OVC Alarm - Overcurrent (Average)
Same family: this code belongs to the Servo & drive alarms family - the page collects all Servo & drive-family codes we have handled, with the common inspection order and spares.
Other brands: see our KUKA, ABB, Yaskawa and Universal Robots field-fix libraries — or the full 10-brand hub.

Frequently asked questions

QWhat does the FANUC srvo-043 alarm mean?

Regenerative energy from decelerating axes exceeded what the discharge circuit could absorb. The DC link voltage rose too high and the amplifier shut down to protect itself. We see this alarm constantly when servicing FANUC R-30iA / R-30iB / R-30iB Plus systems, and the first on-site pass usually pins down the cause. FANUC srvo-043 sits in the servo & drive family; on our work orders the highest-frequency trigger for this code is "Frequent high-speed deceleration with heavy load (cycle too aggressive)".

QCan I clear a FANUC srvo-043 alarm myself?

Whether FANUC srvo-043 clears on its own depends on the outcome of "Reduce acceleration/deceleration or speed on the offending moves and see if the alarm stops". Finish the flow with "On systems with an external regenerative unit, check its alarm LEDs" to confirm FANUC srvo-043 - do not skip it. If that step is clean, the second most frequent cause on FANUC srvo-043 is "Discharge resistor failure or its fan stopped". When FANUC srvo-043 keeps coming back it is not a one-off trigger - especially if On systems with an external regenerative unit, check its alarm LEDs is where you get stuck. Do not keep producing through FANUC srvo-043.

QFor servo alarms like FANUC srvo-043, how do you tell motor from drive?

The commonest causes we see on FANUC srvo-043 are "Frequent high-speed deceleration with heavy load (cycle too aggressive), Discharge resistor failure or its fan stopped, Regenerative discharge unit fault", so we stock the van against those. For FANUC srvo-043 specifically, we bring the scope and meter; motors and drives are stocked by type, and most cases are measured before parts are ordered. For FANUC srvo-043, on servo alarms we specifically avoid misjudgement: waveform first, parts second, so customers skip needless swaps. Before we roll, tell us what FANUC srvo-043 shows on the iPendant ALARM screen (SRVO / MOTN / SYST / INTF prefixes) together with the amplifier's 7-segment status code and what the machine was doing - phone or video triage is free.

This page on FANUC srvo-043 is based on the field experience of the Henghuan Robotics repair team. Alarm explanations are our own summary for troubleshooting reference and may differ across controller and software versions — if unsure, verify against FANUC documentation or reach out to us. Henghuan is an independent service provider with no affiliation or endorsement by FANUC.