5 Troubleshooting 
 
 
5
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5.1.3 Torque 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. The control power 
voltage is abnormal.
After disconnecting CN1, CN2, CN3 and CN4, the 
fault persists.
Measure AC voltage between L1C and L2C.
2. The 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".
Set the S-ON to 
ON.
The operation 
panel displays "Er.
xxx".
Remove the fault.
Shaft of the servo 
motor is in free 
running status.
1. The S-ON signal 
is invalid.
Set operation panel to servo status display and 
view whether the operation panel displays "rdy" 
rather than "run".
Check whether any parameter in groups H03 and 
H17 is set for FunIN1(S-ON). If yes, check that the 
corresponding DI is set to ON. If not, allocate the 
function and set the corresponding DI to ON. See 
group H03 in Chapter 7 for details on setting of 
input terminal parameters.
If a parameter in group H03 has been set for 
FunIN1(S-ON)  and logic of corresponding DI is 
logic, but the operation panel still displays "rdy". 
In this case, check whether the DI terminal is 
connected correctly by referring to Chapter 3 in the 
IS620P User Manual.
After the preceding causes are removed, the operation panel should display "run".