5 Troubleshooting 
 
 
5
- 35 -
During Startup Fault Symptom Cause Conrming Methods
Servo motor 
jitters at low 
speed.
Motor speed is not 
steady.
The gain is set 
improperly.
Perform automatic gain tuning.
Motor shaft vibrates 
left and right.
The load inertia ratio 
(H08-15) is too large.
If servo motor can run safely, perform inertia 
auto-tuning and perform automatic gain tuning.
After preceding causes are removed, servo motor can operate normally.
Servo system 
runs normally.
Positioning 
inaccurate
Unsatisfactory position 
deviation is generated.
Conrm input reference pulse counter (H0B-
13), feedback pulse counter (H0B-17) and 
mechanical stop position according to the 
following steps.
5.1.2 Speed Control
During Startup Fault Symptom Cause Conrming Methods
Connect control 
power L1C/L2C 
and main power 
L1/L2 and R/S/
T.
The LED display is 
not on or does not 
display "rdy".
1. Control 
power voltage is 
abnormal.
After disconnecting CN1, CN2, CN3 and CN4, the 
fault persists.
Measure AC voltage between L1C and L2C.
2. Main power 
voltage is 
abnormal.
For single-phase 220 V mode, measure AC voltage 
between L1 and L2. When DC bus voltage amplitude 
(voltage between 
 and 
) is lower than 200 V, "nrd" 
is displayed.
For three-phase 220/380 V model, measure AC 
voltage between R, S and T. When DC bus voltage 
amplitude (voltage between 
 and 
) is lower than 
460V, "nrd" is displayed.
3. The program 
burning terminal is 
shorted.
Check whether the program burning terminal is 
shorted.
4. The servo drive 
is faulty.
-
The operation 
panel displays "Er.
xxx".
Remove the fault.
After the preceding causes are removed, the operation panel should display "rdy".