10   Troubleshooting and Maintenance
10 - 10
OMNUC G5-series (Pulse-train Input Type) AC Servomotors and Servo Drives User’s Manual
10-4 Troubleshooting
If an error occurs in the machine, determine the error conditions from the alarm display and operation 
state, identify the cause of the error, and take appropriate measures.
10-4-1 Error Diagnosis with Alarm Displays
Alarm No.
Name Cause Measures
Main
Sub
11 0 Control Power Supply 
Undervoltage
The voltage across the positive and 
negative terminals in the control power 
supply converter dropped below the 
specified value.
200-V products: Approx. 145 VDC
(Approx. 100 VAC)
• The power supply voltage is low. A 
momentary power interruption 
occurred.
• Insufficient power supply capacity:
The power supply voltage dropped 
because there was inrush current 
when the main power supply was 
turned ON.
• The Servo Drive is faulty (circuit fault).
Measure the voltage across the L1C and 
L2C lines on the connectors and the 
terminal block.
• Increase the power supply voltage. 
Change the power supply.
• Increase the power supply capacity.
• Replace the Servo Drive.
12 0 Overvoltage The power supply voltage exceeded the 
allowable input voltage range, causing 
the voltage across the positive and 
negative terminals in the converter to 
exceed the specified value. The power 
supply voltage is high. The voltage was 
suddenly increased by the phase 
advance capacitor or the uninterruptible 
power supply (UPS).
200-V products: Approx. 400 VDC 
(Approx. 280 VAC)
• The Regeneration Resistor wiring is 
broken.
• The External Regeneration Resistor is 
inappropriate and cannot absorb all of 
the regenerative energy. The load 
inertia is too large, gravitational torque 
on the vertical axis is too large, or 
there is some other problem to absorb 
the regenerative energy.
• The Servo Drive is faulty (circuit fault).
Measure the voltage across the L1, L2, 
and L3 lines on the connectors and the 
terminal block.
Input the correct voltage. Remove the 
phase advance capacitor.
• Use a tester to measure the resistance 
of the external resistor between the B1 
and B2 terminals on the Servo Drive. If 
the resistance is infinite, the wiring is 
broken. Replace the external resistor.
• Change the regeneration resistance 
and wattage to the specified values. 
Calculate the regenerative energy and 
connect an External Regeneration 
Resistor with the required 
regeneration absorption capacity. 
Reduce the descent speed.
• Replace the Servo Drive.