Troubleshooting
8-2
8.1 Self-diagnostic Function
8.1.1 Operation Monitor LEDs of Control Unit
• The control unit has a self-diagnostic function which identifies errors and stops operation if
necessary.
• When an error occurs, the status of the status indicator LEDs on the control unit vary, as
shown in the table above.
LEDs related to self-diagnostic errors
LED display
Description
Operation
status
RUN
(Green)
PROG
(Green)
ERR/ALM
(Red)
In normal
condition
ON OFF OFF
Normal operation Operating
OFF ON OFF
Program mode
LED does not flash even if the forcing
output is performed in program mode.
Stop
Flashes
(Note 1)
Flashes
(Note 1)
OFF
Forcing input/output in RUN mode
RUN and PROG. LEDs flash
alternately.
Operating
Flashes
Flashes
OFF
During version upgrade Stop
In
abnormal
condition
ON OFF Flashes
Self-diagnostic error (During operation) Operating
OFF ON Flashes Self-diagnostic error (During stop) Stop
OFF ON ON
System watchdog timer has been
activated
Stop
(Note 1): The flashing is repeated every 1 second. (ON for 0.5 seconds ⇔ OFF for 0.5 seconds)
(Note 2): The LEDs flash quickly while upgrading the version. The flashing changes to a slow flashing while rewriting
the version.
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