FANUC SRVO-046 OVC Alarm: Diagnosing Overcurrent Trips Before You Replace the Servo Amplifier

The cell trips, the line stops, and the alarm screen has SRVO-046 SERVO OVC on G1 A2 staring at you. Someone, somewhere, is about to suggest replacing the amplifier. Sometimes the amp is the answer. More often it is not, and a thirty-minute diagnostic saves a four-figure part swap. At Probot Systems we see SRVO-046 most often on older ARC Mate and SR-6iA arms, but the R-30iB cabinets behave the same way once payload data or a mechanical bind starts pushing a joint past its current envelope.

This post is written for technicians and integrators chasing SRVO-046 on R-30iA Mate, R-30iB, and R-30iB Plus controllers. The diagnostic flow assumes the alarm has been logging more than once. A single OVC after a real crash is not the same problem as recurring OVC during normal cycle.

What this error actually means

SRVO-046 is the OVC (overcurrent) alarm on a servo amplifier. The PNT1-100 cross-reference on page 1025 of the FANUC error code manual confirms the path: “PNT1-100 OVC alarm Cause: This Alarm is echoed to the PLC when SRVO-046 SERVO OVC alarm (Group:%d Axis:%d) is posted. Refer to the Teach Pendant alarm screen for group and axis number. Refer to SRVO-046 for the cause.” That is FANUC’s way of telling you the amplifier saw an instantaneous current that exceeded its limit on the named axis.

Mechanically, this is different from SRVO-043. SRVO-043 is a thermal average, SRVO-046 is a peak. The amp pulled too many amps in one moment, the protection circuit cut servos, and the controller locked out the group. The trigger is either the load on the motor (payload, bind, sticking brake) or the amplifier hardware itself.

Most common causes, in order of probability

In order of how often we land on each one:

1. Payload, mass, or center of gravity not configured for current tooling. Tooling gets changed, payload schedule does not get updated, the controller plans accelerations the motor cannot deliver inside the OVC envelope. Surfaces most often on J2 or J3 of welding cells and palletizers. A DIY Robotics thread on combined SRVO-046 and SRVO-050 starts the conversation around payload for exactly this reason (reference thread).
2. Brake not fully releasing on the affected axis. A brake that is dragging looks identical to a mechanical bind from the amp’s point of view. Current spikes when motion starts, OVC fires, you reset, repeat. Brake-release wiring and the 24V supply are quick to verify.
3. Mechanical bind, harness pulling on the wrist, or gripper hitting a fixture. Any time the motor has to push against unexpected resistance, you get peak current well above what the cycle should require. We have seen J5 OVCs caused by a dress pack that slipped out of its strain relief.
4. Servo motor or amplifier developing a short. This is real, but rarely the first thing to find. If both check out, swap as a pair to avoid pumping a failing motor into a fresh amp.
5. Excessive or unbalanced load on acceleration. Heavy parts grabbed off-center create peak inertia that the motion planner does not anticipate. A Reddit user working on a 24-year-old ARC Mate 120i had to chase exactly this combination of age, payload, and cycle (ARC Mate thread).

How to diagnose in under 10 minutes

Step 1. Note the group and axis. SRVO-046 always names G: A:. The diagnostic differs by joint, so write it down.

Step 2. Ask the operator what changed. New tooling, new program, new operator, replaced gripper, anything. Most SRVO-046 cases trace back to a change that happened in the last week or two.

Step 3. Power off, release the brake on the affected axis, and check the joint moves freely by hand. A sticky brake or a mechanical bind shows up here instantly. Do not skip this even if the program “ran clean yesterday.”

Step 4. Read the payload schedule. MENU > SYSTEM > Motion > Payload. Compare mass, CoG, and inertia to the actual tooling. If anything is off by more than ten percent, fix payload before doing anything else.

Step 5. Check the brake-release wiring and the 24V brake supply. A weak supply can leave a brake half-engaged, and a half-engaged brake reads exactly like a bind to the amplifier (reference thread).

Step 6. Inspect the encoder signal on the affected axis. A noisy encoder can drive the amplifier into oscillation, which reads as overcurrent on every cycle. Reseating the encoder cable connector is a one-minute test.

Step 7. If the bind is clear and payload is correct, swap the amplifier with a known-good identical model and watch the next shift. If the alarm follows the axis, the motor is suspect. If it stays with the cabinet, it was the amp (ARC Mate thread).

How to fix it

Match the fix to what you found in the diagnostic.

If payload was wrong: run PAYLOAD ID with the real tooling installed. Save the result. Run the program at full speed for one full cycle to confirm. Do not skip the full-speed run. SRVO-046 lives in the peak, not the average.

If the brake was dragging: verify the brake-release voltage at the joint connector and the brake coil resistance. A weak brake supply gets fixed at the cabinet. A dragging coil means the motor brake assembly is the next part.

If you found a mechanical bind: clear it, run the diagnostic again, and verify with the full-speed pass. Do not patch a harness strain relief with zip ties and call it done. A dress pack that worked loose once will do it again.

If the encoder is the issue: replace the cable first. Encoder noise from a flexed cable is the cheapest fix in this entire list and the one most often skipped.

If amp and motor swap is the conclusion: do them as a pair on high-mileage robots, and back up your mastering data before pulling either part.

When to call a specialist

Call us when payload is verified, brakes release cleanly, no mechanical bind is found, and SRVO-046 still drops on the same axis. At that point you are looking at an amp or motor change, and on production welders that is a half-day job with mastering implications.

Same applies if SRVO-046 is showing up together with SRVO-050 (collision detect) on the same shift. The two alarms share root causes around payload and mechanics, and you want one diagnostic pass to cover both rather than chasing each in isolation.

contact us for a service call, or set up a maintenance preventive contract so payload schedules and dress packs get audited before they generate this alarm in the middle of a shift.

Related errors to check

• SRVO-050 Collision Detect: same root-cause family on payload and mechanics. Often logs in the same cycle as SRVO-046 on cells with stale payload schedules.
• SRVO-043 SERVO DCAL: thermal version of an overcurrent problem. If both alarms appear, the cycle is asking too much of the joint.
• SRVO-045 SERVO HCAL: high-current alarm. Different threshold, same family of causes. Treat together if both appear.

Probot Systems is a FANUC integrator based in Lévis, Quebec. We service older ARC Mate and R-30iA Mate arms as well as current R-30iB Plus cells across Canada and the US, and we know which SRVO-046 diagnostics are worth doing before ordering parts. If your cell is throwing OVC on the same joint twice in a week, that is a contact us conversation.