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FANUC Alarm SRVO-038 — SERVO Pulse mismatch

Error
Hardware
Pulsecoder (encoder)
Controllers
R-J3iB / R-30iA / R-30iB
FANUC class
SERVO2
Hardware family
FANUC Pulsecoder, backup battery and position loss alarms

Manufacturer wording — SERVO Pulse mismatch (G:%d A:%d)
The manual prints placeholders; your controller fills them in with the real group, axis or number.

FANUC SRVO-038 (“SERVO Pulse mismatch”): A pulse count detected when the controller was turned off differs from that detected when the controller was turned on. First check: First perform an APC reset and remaster the robot: 1. Likely part: Pulsecoder (Pulsecoder (motor encoder)).

Updated 2026-10-22 · LogrobotLM reference

Description

A pulse count detected when the controller was turned off differs from that detected when the controller was turned on. This alarm is asserted after exchange of the pulse coder or battery for backup of the pulse coder data, or loading backup data to the main board.

Remedy

First perform an APC reset and remaster the robot: 1. Press MENUS. 2. Select SYSTEM. 3. Press F1, [TYPE]. 4. Select MASTER/CAL. 5. Press F3, [RES-PCA]. 6. Press RESET. 7. Perform a Cold start. WARNING: By completing the next step you will be altering the positional reference for the robot since you are replacing hardware. You must slowly verify all positional data and touch-up any paths or points that have changed. Otherwise, you could injure personnel or damage equipment. 8. Remaster the robot if needed. If remastering is performed, you must verify all of your robot paths to prevent damage to equipment. If the pulse mismatch is not reset: 1. Check the pulse coder cable from the motor. 2. Check the internal cable set next. 3. Check the P1 cable from the robot to the controller, verify that there are no pins damaged at the robot base connection and that there is not damage to the cable. 4. Replace the pulse coder and remaster as stated in the APC RESET procedure above.

Field diagnosis

The number of pulses read at startup differs from the one stored at shutdown: mastering file loaded from another state or another robot, incorrect software brake setting, or axis moved while powered off.

What to check

  • Read the history: with SRVO-222, deal with 222 first.
  • Correct the brake setting if it is involved, reload the mastering file of the correct robot, then Pulsecoder reset (system variable or RES_PCA in MASTER/CAL), power cycle, and mastering.
  • Note: Appears legitimately after replacing the Pulsecoder or the batteries.
  • Diagnostic sequence “Pulsecoder battery sequence”: Complete sequence after loss of position: BZAL (SRVO-062) at power-up, then 075 "position not established" after the encoder reset, then mastering. New batteries with the power on, Pulsecoder reset (RES_PCA or system variable), power cycle, QUICK MASTER if the reference exists (otherwise full mastering), jog of about ten degrees on each affected axis, RESET.

Part to check / replace

FANUC SRVO-038 points to the hardware below — start here before ordering.

Tap a part for every code that points to it — and verify the exact variant for your controller before ordering.

Related codes

SRVO-062SERVO BZAL alarmSRVO-075WARN Pulse not establishedSRVO-222SERVO Lack of Amp (Amp:…)SRVO-036SERVO Inpos time overSRVO-037SERVO IMSTP inputSRVO-039SERVO Motor speed excess

Same hardware involved

SRVO-061PulsecoderSRVO-063PulsecoderSRVO-064PulsecoderSRVO-066Pulsecoder

Indicative field information — the robot manufacturer's manual and safety procedures always prevail. Never bypass a safety device; apply lockout/tagout (LOTO) before any physical intervention. How this reference is built →