Chapter 11 Troubleshooting
11-1
The following explains contents, diagnosis and corrective actions for various errors that can occur during system operation.
11.1 Basic Procedures of Troubleshooting
System reliability not only depends on reliable equipment but also on short downtimes in the event of faults.
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 operating 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?
11.2 Troubleshooting
This section explains the procedure for determining the cause of troubles as well as the errors and corrective actions.
Is the power LED turned OFF? 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? Flowchart used when the RUN turned OFF.
I/O module doesn’t operate properly Flowchart used when the output load of the output module
doesn’t turn on.
Program cannot be written Flowchart used when a program can’t be written to the PLC