TL;DR

A brake fault alarm on the R-2000iC is a safety-critical condition. Do not jog or run the robot until the brake is confirmed functional. Check solenoid voltage and coil resistance first.

What you might see

SRVO-004 or SRVO-023 brake alarm on controller
arm drops or drifts when power is cut
brake release solenoid not clicking audibly
axis moves sluggishly in T1 mode

Likely causes

Tap to mark as ruled out

Brake solenoid coil failure causing the brake to fail to release or hold
Worn brake friction material reducing holding torque below specification
Brake power supply voltage low, preventing full solenoid actuation
Brake release circuit wiring fault or failed relay in the control cabinet

Required tools

Multimeter (resistance and voltage)
FANUC R-30iB controller access (alarm screen)
Mechanical arm support stand
LOTO kit
FANUC R-2000iC Maintenance Manual

Safety first

A brake fault on a gravity-loaded axis is a drop hazard. Mechanically support the arm before any brake testing or repair.
Never jog or run a robot with a known brake fault. A failed brake can allow the arm to drop at full speed.
Lock out the controller main power before measuring coil resistance or performing any wiring inspection on the brake circuit.

Procedure

7 steps · ~45 min

1
Record the alarm code from the FANUC controller. SRVO-004 is a brake abnormality; the axis number in the alarm identifies the affected joint.[1]
2
Do not attempt to jog or run the affected axis until the brake is confirmed operational. A failing brake on the gravity-loaded J2 or J3 axis is a drop hazard.
Warning: Support the robot arm with a mechanical support stand before releasing or testing the brake on a gravity-loaded axis. An unsupported arm can drop and cause serious injury.
3
Lock out the controller. Measure the resistance of the brake solenoid coil at the motor connector for the affected axis. Compare to FANUC specification. An open circuit confirms a failed coil.[1]
4
If the coil is OK, restore power and measure the brake release voltage at the solenoid terminals while commanding a brake release. Low voltage indicates a supply or wiring fault.
5
Trace the brake release circuit from the servo amplifier through the relay and wiring harness to the motor connector. Check for open circuits, burnt relay contacts, or loose connections.
6
If coil resistance is within spec and voltage is correct but the brake does not hold properly, the brake friction material is worn. Motor replacement or brake rebuild by a FANUC-certified technician is required.
7
After any brake repair, perform a brake holding test per FANUC procedure before returning the robot to automatic operation. The robot must hold its position under gravity load with no servo power.

Sources

FANUC R-2000iC Robotic Arm Maintenance Manual, FANUC
FANUC R-2000iC Robot Maintenance Manual, brake system maintenance and alarm diagnosis procedures (general)
View source

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