Chapter 11 Troubleshooting
Chapter 11 Troubleshooting
The following explains contents, diagnosis and corrective actions for various errors that can occur during system
operation.
System reliability not only depends on reliable equipment but also on short downtimes in the event of fault. The
short discovery and corrective action is needed for speedy operation of system. The following shows the basic
instructions for troubleshooting.
(1) Visual checks
Check the following points.
• Machine operating condition (in stop and operation status)
• Power On/Off
• Status of I/O devices
• Condition of wiring (I/O wires, extension and communications cables)
• Display states of various indicators (such as POWER LED, RUN LED, ERR LED and I/O LED)
After checking them, connect peripheral devices and check the operation status of the PLC and the
program contents.
(2) Trouble Check
Observe any change in the error conditions during the following.
• Switch to the STOP position, and then turn the power on and off.
(3) Narrow down the possible causes of the trouble where the fault lies, i.e.:
• Inside or outside of the PLC ?
• I/O module or another module?
• PLC program?
Flowchart used when the POWER LED is turned Off.
Is the ERR LED flickering ?
Flowchart used when the ERR LED is flickering.
Are the RUN LED turned
Off ?