10.2  Alarm Displays
10-9
10
Maintenance, Inspections, and Troubleshooting
A.520:
Vibration Alarm
Abnormal vibration was detected 
at the motor speed.
Check for abnormal noise from the 
servomotor, and check the speed 
and torque waveforms during oper-
ation.
Reduce the motor speed or reduce 
the speed loop gain (PnAC2).
The moment of inertia ratio 
(Pn103) value is greater than the 
actual value or is greatly 
changed.
Check the moment of inertia ratio.
Set the moment of inertia ratio 
(Pn103) to an appropriate value.
A.521:
Autotuning Alarm
(Vibration was 
detected while 
executing the one-
parameter tuning, 
EasyFFT, or tuning-
less function.)
The servomotor vibrated consid-
erably while performing tuning-
less function.
Check the motor speed waveform.
Reduce the load so that the moment 
of inertia ratio falls within the 
allowable value, or raise the load 
level using the tuning-less levels 
setting or reduce the rigidity level.
The servomotor vibrated consid-
erably during one-parameter tun-
ing or EasyFFT.
Check the motor speed waveform.
Check the operation procedure of 
corresponding function and take a 
corrective action.
A.710:
A.720:
Overload 
A.710: High Load
A.720: Low Load
Incorrect wiring or contact fault 
of servomotor and encoder.
Check the wiring.
Confirm that the servomotor and 
encoder are correctly wired.
Operation beyond the overload 
protection characteristics.
Check the servomotor overload 
characteristics and executed run 
command.
Reconsider the load conditions and 
operating conditions. Or, increase 
the motor capacity.
Excessive load was applied 
during operation because the ser-
vomotor was not driven due to 
mechanical problems.
Check the executed operation refer-
ence and motor speed.
Remove the mechanical problems.
A.7A3: 
Control Board 
Overheat
The surrounding air temperature 
of the SERVOPACK is too high.
Measure the surrounding air tem-
perature of the SERVOPACK.
Improve the installation conditions 
of the SERVOPACK to reduce the 
surrounding air temperature.
A.810:
Encoder Backup Error
(Only when an 
absolute encoder is 
connected.)
(Detected on the 
encoder side.)
Alarm occurred when the power 
to the absolute encoder was ini-
tially turned ON.
Check to see if the power was 
turned ON initially.
Set up the encoder.
The encoder cable disconnected, 
and connected again.
Check to see if the power was 
turned ON initially.
Confirm the connection and set up 
the encoder.
The power from both the control 
power supply (+5 V) from the 
SERVOPACK and the battery 
power supply is not being sup-
plied.
Check the encoder connector bat-
tery or the connector contact status.
Replace the battery or take similar 
measures to supply power to the 
encoder, and set up the encoder.
An absolute encoder fault 
occurred.
−
If the alarm cannot be reset by set-
ting up the encoder again, replace 
the servomotor.
A.820:
Encoder Checksum 
Error
(Detected on the 
encoder side.)
An encoder fault occurred. −
• Absolute encoder 
Set up the encoder again using 
Fn008. If the alarm still occurs, 
the servomotor may be faulty. 
Replace the servomotor.
• One-turn absolute encoder or 
incremental encoder 
The servomotor may be faulty. 
Replace the servomotor.
A.830:
Absolute Encoder 
Battery Error
(The absolute encoder 
battery voltage is 
lower than the 
specified value.)
The battery connection is incor-
rect.
Check the battery connection. Reconnect the battery.
The battery voltage is lower than 
the specified value 2.7 V.
Measure the battery voltage. Replace the battery.
(cont’d)
Alarm Number:
Alarm Name
(Alarm Description)
Cause Investigative Actions Corrective Actions