What the SRVO-038 alarm means

The controller detected a pulse count mismatch for the axis between power cycles - the feedback position jumped unexpectedly. This is a high-frequency ticket for our FANUC repair team, and on R-30iA / R-30iB / R-30iB Plus systems one inspection usually identifies the fault.

Most common causes

  • Battery voltage dropped during power-off
  • Encoder cable intermittently disconnected
  • Pulse coder internal fault
Field note: The top-listed cause has the highest hit rate, so checking it first narrows things down fast.

Step-by-step field fix

  1. Check battery voltage and encoder connectors first
  2. RES_1PA reset, cycle power
  3. Re-master the axis and verify against witness marks
  4. If the alarm returns repeatedly, replace the pulse coder (motor assembly)
Safety first: For FANUC srvo-038, battery swaps carry reverse-polarity and short-circuit risk that can burn the measuring board; and a dead battery means lost zero data and a stopping re-master. The self-serviceable action is Check battery voltage and encoder connectors first; anything past that falls under battery polarity and zero data and needs a certified engineer.

How we diagnose calibration alarms on site

FANUC srvo-038 belongs to the battery & mastering family. On FANUC srvo-038 the failing stage is absolute encoders inside alpha-i motors, position memory held by the encoder battery pack on the R-30iB Plus / R-30iB Mate Plus / R-30iA - low battery voltage losing the absolute position memory, which then demands a fresh zero master - two jobs in one. We start reading FANUC srvo-038 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-038 runs: battery pack supply -> absolute position count -> memory held across power-off -> voltage too low loses it -> re-master required.

After mastering for FANUC srvo-038, verification is mandatory: Mastering must be verified, not celebrated. We run repeat-positioning on a fixed reference and spot-check the customer's live production points. If points are visibly off, the mastering datum is suspect, or a mechanical zero mark has shifted - for example after a reducer was replaced. In that case the datum is re-established rather than the master repeated. The master record, including per-axis values and verification results, is handed over in writing.

Field notes on this page cover FANUC srvo-038 (Pulse Mismatch (Group / Axis)); written by the Henghuan repair team, updated 2026-10-01.

Real Field Case

Machine: FANUC M-710iC/50 (2016)

Symptom: An M-710iC/50 raised SRVO-038 (pulse count mismatch) with a position deviation on one axis.

What we did: We determined the axis lost data during a power loss, replaced the battery, mastered that axis and re-checked the adjacent axes.

Result: Deviation cleared after mastering, accuracy re-check passed; done in about 3 hours.

Not sure? Don't force it — contact an engineer

Give us the alarm code, robot model and the action at the moment of the alarm, and our engineers can give you a quick read — phone or video remote diagnosis is free.

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Hotline: +86-20-39029800 · WhatsApp: +86-188-1886-2860

Related Battery & Mastering alarms

SRVO-062 — BZAL Alarm (Group / Axis) SRVO-065 — BLAL Alarm - Battery Voltage Low SRVO-075 — Pulse Position Mismatch SRVO-027 — Robot Not Mastered
Same family: this code belongs to the Battery & mastering alarms family - the page collects all Battery & mastering-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-038 alarm mean?

The controller detected a pulse count mismatch for the axis between power cycles - the feedback position jumped unexpectedly. This is a high-frequency ticket for our FANUC repair team, and on R-30iA / R-30iB / R-30iB Plus systems one inspection usually identifies the fault. FANUC srvo-038 sits in the battery & mastering family; on our work orders the highest-frequency trigger for this code is "Battery voltage dropped during power-off".

QCan I clear a FANUC srvo-038 alarm myself?

Whether FANUC srvo-038 clears on its own depends on the outcome of "Check battery voltage and encoder connectors first". Finish the flow with "If the alarm returns repeatedly, replace the pulse coder (motor assembly)" to confirm FANUC srvo-038 - do not skip it. If that step is clean, the second most frequent cause on FANUC srvo-038 is "Encoder cable intermittently disconnected". Do not chase takt through a repeating FANUC srvo-038. Left alone, battery & mastering faults tend to graduate from repairable to must-replace.

QWhen you handle FANUC srvo-038, will my programs and frames get lost?

The commonest causes we see on FANUC srvo-038 are "Battery voltage dropped during power-off, Encoder cable intermittently disconnected, Pulse coder internal fault", so we stock the van against those. For FANUC srvo-038 specifically, we carry the model's battery pack and mastering fixtures; battery changes belong in scheduled maintenance, not in alarm response. For FANUC srvo-038, on battery and mastering alarms we back up programs and points first, master second and verify precision on site. Before we roll, tell us what FANUC srvo-038 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.

The content on FANUC srvo-038 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 FANUC documentation, or contact us to confirm. Henghuan is an independent service provider with no affiliation or endorsement by FANUC.