FANUC SRVO-068 DTERR Alarm Troubleshooting & Repair
What the SRVO-068 DTERR Alarm Means
The controller displays the alarm exactly as SRVO-068 DTERR alarm (Grp:i Ax:j), where Grp identifies the motion group and Ax identifies the specific axis reporting the fault. The FANUC maintenance description for this code states that the serial Pulsecoder does not return serial data in response to a request signal sent by the servo amplifier. This is a feedback-communication fault, not a motion-command fault: the amplifier asked the Pulsecoder on that axis for its position data and got no valid reply.
When SRVO-068 trips, the system drops into a servo alarm state. Servo power to the affected axis is disabled, the robot cannot be jogged or run on a program until the alarm is cleared, and remaining axes in the same group are typically held as well. The alarm by itself only confirms a break in the serial link between amplifier and Pulsecoder — it does not identify which link component failed.
Common Causes Behind DTERR, CRCERR, And STBERR
The most likely cause, and the first item in the OEM troubleshooting order, is a connector or cable problem on the feedback line: a loose, damaged, or intermittently seated connector at the servo amplifier (CRF8 on R-30iB Mate and R-30iB Mate Plus six-axis amplifiers) or at the motor-side Pulsecoder connector (RMP1 or RP1 depending on controller and cable naming) can prevent the amplifier’s request from reaching the Pulsecoder or prevent the reply from getting back. The second most likely cause is poor or missing shield grounding in the cabinet, which lets electrical noise corrupt the serial data. Beyond wiring, a failed Pulsecoder or a defective servo amplifier feedback interface can produce the same symptom.
SRVO-068 rarely appears alone in the fault history. Related codes point to the same feedback link:
- SRVO-068 DTERR — Pulsecoder does not return serial data when requested.
- SRVO-069 CRCERR — serial data was disturbed during communication, pointing to noise, grounding, or cable/connector issues on the same link.
- SRVO-070 STBERR — start and stop bits of the serial data are abnormal, indicating the same class of feedback-link disturbance.
All three should be treated as one feedback-link fault group affecting FANUC R-30iA, R-30iB, and R-30iB Plus controllers, regardless of which robot series or amplifier model is installed.
Step By Step Troubleshooting
Before opening any cabinet or disconnecting connectors, lock out and tag out the robot’s main disconnect and follow the facility’s energy-control procedure; servo amplifiers and connected cabling can retain hazardous voltage even after the controller is powered down.
With power removed and verified:
- Record the exact alarm text, including the group and axis reported, and pull the alarm history for repeat occurrences or companion SRVO-069/SRVO-070 codes.
- Inspect and reseat the robot connection cable at the servo amplifier connector and at the motor-side Pulsecoder connector; check for bent pins, corrosion, and partial engagement.
- Inspect cable routing for pinch points, abrasion, or excessive flex, and verify the cable shield is securely grounded in the cabinet.
- Check cabinet grounding points for corrosion or loose hardware.
- If connectors and grounding check out, substitute or test the Pulsecoder, then the feedback cable, then the servo amplifier in that order before concluding a component has failed.
Restore power only after connectors are fully reseated and guards are back in place.
Clearing The Alarm And Verifying The Fix
SRVO-068, SRVO-069, and SRVO-070 clear the same way: correct the underlying connection, shielding, or component fault, then reset the alarm and attempt motion on the affected axis. Do not simply reset and return to production if the fault reappears on the next move — that indicates an intermittent connector, cable, or Pulsecoder problem rather than a one-time event.
After any connector reseating or grounding correction, cycle power and confirm the alarm does not return under normal jogging and program motion. If the Pulsecoder, feedback cable, or servo amplifier was replaced, verify the replacement part’s compatibility with the robot model, axis, motor part number, amplifier type, and controller revision before returning the robot to service — SRVO-068 alone does not confirm which part number is correct. Confirm the encoder’s mechanical coupling, connector condition, and feedback output on any replaced or repaired Pulsecoder, and run the axis through its full range under program control to confirm the alarm history stays clear before closing out the repair.
When It Points To A Hardware Failure
Connector and grounding issues typically clear after reseating or correcting the ground and do not return. A hardware failure is more likely when the alarm recurs immediately after a clean connector check, when it appears intermittently during motion but not at rest (suggesting a cracked conductor or damaged connector pin inside the cable), or when it appears consistently on one axis regardless of cable substitution.
A failed Pulsecoder will not return serial data even with a confirmed-good cable and connector; substituting a known-good Pulsecoder on the same axis, where practical, isolates this. A damaged feedback cable — broken conductors, intermittent crimps, pin damage, contamination, or shield discontinuity — produces the same symptoms and is confirmed by substitution or continuity testing. A defective servo amplifier feedback interface is the least common cause and is the OEM’s fourth corrective step for a reason: it should be confirmed only after the Pulsecoder, cable, and grounding have been ruled out, since amplifier replacement is more disruptive and costly.
How Robotics Integration Helps
Robotics Integration supports FANUC R-30iA, R-30iB, and R-30iB Plus systems reporting SRVO-068 DTERR, SRVO-069 CRCERR, or SRVO-070 STBERR with remote troubleshooting help to walk through connector, cable, and grounding checks before any part is pulled. Where a component has failed, we handle Pulsecoder repair or replacement, servo amplifier component-level repair, and feedback cable replacement, matched to the robot model, axis, motor part number, and controller revision involved.
On-site service is available for cases where cabling, connectors, or grounding need to be inspected or corrected in place, or where a hardware swap needs to happen on the production floor rather than shipped out. Repaired Pulsecoders and amplifiers are checked for connector and insulation condition, feedback-communication accuracy, and functional servo response before being returned, with loaded or burn-in testing used where the equipment and axis configuration allow it to catch intermittent faults that a simple power-up would not show.
Looking up a different code? See the full FANUC and robot alarm code list, or read about our FANUC robot repair.
What To Send Before You Call
To get a faster read on an SRVO-068, SRVO-069, or SRVO-070 alarm, have the following ready before you call: the exact controller model (R-30iA, R-30iB, or R-30iB Plus), the full alarm text as displayed including group and axis, the alarm history showing whether the code is a single event or a repeat, which axis is affected, and what the robot was doing at the moment the alarm tripped — running a program, jogging, or sitting idle at power-up.
Call 1-602-449-1556 to talk through the alarm with a technician, get direction on connector and grounding checks, or arrange Pulsecoder, cable, or servo amplifier repair and on-site support for FANUC R-30iA, R-30iB, and R-30iB Plus robots.
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