Maintenance
and Troubleshooting
9–7
Maintenance and Troubleshooting
If the CPU will not enter the Run mode (the RUN indicator is off), the problem is
usually in the application program, unless the CPU has a fatal error. If a fatal error
has occurred, the CPU LED should be on. (You can use a programming device to
determine the cause of the error.)
Both of the programming devices, Handheld Programmer and DirectSOFT
, will
return an error message describing the problem. Depending on the error, there may
also be an AUX function you can use to help diagnose the problem. The most
common programming error is “Missing END Statement”. All application programs
require an END statement for proper termination. A complete list of error codes can
be found in Appendix B.
If the CPU indicator is on, a fatal error has occurred in the CPU. Generally, this is not
a programming problem but an actual hardware failure. You can power cycle the
system to clear the error. If the error clears, you should monitor the system and
determine what caused the problem. You will find this problem is sometimes caused
by high frequency electrical noise introduced into the CPU from an outside source.
Check your system grounding and install electrical noise filters if the grounding is
suspected. If power cycling the system does not reset the error, or if the problem
returns, you should replace the CPU.
Communications Problems
If you cannot establish communications with the CPU, check these items.
S The cable is disconnected.
S The cable has a broken wire or has been wired incorrectly.
S The cable is improperly terminated or grounded.
S The device connected is not operating at the correct baud rate (9600
baud).
S The device connected to the port is sending data incorrectly.
S A grounding difference exists between the two devices.
S Electrical noise is causing intermittent errors.
S The PLC has a bad communication port and should be replaced.
For problems in communicating with DirectSOFT on a personal computer, refer to
the DirectSOFT manual. It includes a troubleshooting section that can help you
diagnose PC problems in communications port setup, address or interrupt conflicts,
etc.
RUN Indicator
CPU Indicator
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