SRVO-044

Check regenerative unit operation

Power on the controller and navigate to MENU > SYSTEM > Variables. Monitor system variable $MCR.$GENOVERRIDE to verify regenerative unit status. Normal value should be 100%. If regenerative unit is failed, this value may show abnormalities or the unit may not engage during deceleration.

On R-30iB systems, you can also check MENU > MAINTENANCE > TEST > Servo Test to view real-time DC link voltage. Normal idle voltage is ~280-300VDC (200V class) or ~530-570VDC (400V class).

Inspect regenerative discharge resistor

Power down and lockout the controller. Open the cabinet and locate the regenerative resistor (typically mounted on cabinet side panel or external). Visually inspect for cracks, burn marks, or discoloration. Measure resistance with a multimeter - typical values are 40-80 ohms for 200V systems. If resistance is infinite or shows significant deviation from nameplate rating, replace the resistor.

Wait minimum 5 minutes after power-down before opening cabinet. Verify DC bus voltage is below 40VDC using the discharge indicator LED or multimeter on the servo amplifier.

Test regenerative unit transistor

Locate the regenerative transistor module on the power supply unit (PSU). Check for diagnostic LEDs - a red LED or no LED may indicate failure. If equipped with Alpha PSU series, check LED1 on the PSU front panel. Refer to the Maintenance Manual MAROCPSB for transistor testing procedures. Measure voltage across the discharge resistor during controlled deceleration - should see voltage rise during regen.

The regenerative transistor typically triggers at ~385-395VDC (200V) or ~750-770VDC (400V). If DC link reaches alarm threshold without transistor engaging, the transistor or control circuit has failed.

Reduce motion profile deceleration

Temporarily reduce deceleration rates to verify if alarm is load-related. Edit robot program and reduce CNT (corner rounding) values or add intermediate waypoints. In MENU > SETUP > Frames, check payload settings - verify $载荷[group].$PAYLOAD matches actual payload. Incorrect payload settings can cause excessive regenerative energy during deceleration.

If alarm only occurs on specific high-speed moves with heavy payloads, consider enabling deceleration ramping by adjusting $SCR.$DECJERK parameters for smoother decel profiles that reduce regen spikes.

Measure incoming AC voltage at controller

With controller powered on, use a true RMS multimeter to measure voltage at the input power terminal block (L1, L2, L3). Record all three phase voltages and verify they are within ±10% of nominal rating on the controller nameplate. Also verify phase-to-phase balance - voltage difference between any two phases should not exceed 2%. Check voltage during alarm occurrence if possible.

Measurements must be taken on live circuits. Use appropriate PPE and insulated tools. Only qualified electricians should perform this measurement.

Check for voltage transients and spikes

Connect a power quality analyzer or oscilloscope with high voltage probes to the AC input for at least one complete production cycle. Look for voltage spikes exceeding 120% of nominal voltage. Check for transients during welding equipment start-up, large motor switching, or other machinery on the same circuit. Document spike amplitude and frequency.

SRVO-044 alarms that occur at random times without robot motion often indicate external voltage spikes. Install a line reactor or isolation transformer if spikes exceed 10% above nominal voltage.

Verify transformer tap settings

If robot is supplied by a dedicated transformer, verify the tap setting matches the actual utility voltage. Taps set too high will supply excessive voltage to the controller. Check the transformer nameplate and verify current tap position. Typical taps are available in 2.5% or 5% increments. Adjust to lower tap if input voltage is consistently at the high end of specification.

After any tap adjustment, verify DC link voltage at MENU > MAINTENANCE > TEST > Servo Test. Target idle DC link voltage should be approximately 1.35 times the line-to-line AC voltage (for three-phase rectified systems).

Inspect line reactor and power filter

Power down and lockout. Visually inspect the AC line reactor (inductor coils at AC input) for overheating, discoloration, or burnt insulation smell. Check all connections for tightness. If equipped with an EMC filter, verify all filter capacitors are intact with no bulging or leakage. A failed line reactor reduces impedance and allows voltage spikes to reach the DC bus more easily.

Line reactors may retain residual magnetic fields. Ensure all power is disconnected before inspection.

Check PSU diagnostic LEDs and alarms

Observe the Power Supply Unit LEDs with controller powered on. Green LED should be steady. Check for additional alarm codes related to power supply. Navigate to MENU > ALARM > Alarm History (F1) and review all alarms around the time SRVO-044 occurred. Look specifically for SRVO-075 (DC link voltage deviation), SYST-035 (Fan alarm), or any PSU-related alarms that may indicate root cause.

On Alpha series PSUs, simultaneous SRVO-044 and fan alarms often indicate overheating of the regenerative section. Check ambient temperature and ensure cabinet fans are operational.