Mitsubishi PLC ERROR

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My Fx3u-48 M suddenly have error.Red LED error light up and all output LED not light up.Sometime,the red LED error not light up and the output LED return to normal cobdition.In Mitsubishi GOT ,have error message“Communication error ,Refer to System Alarm in Utility Menu."

Where is Utility Menu?What wrong my PLC and what i should do?



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Dear KongFah,

By the information you gave, it seems that your PLC is facing intermittent hardware problems. 

When the FX2N ERROR LED is lit solid it is likely to be internal hardware problem or watchdog timer - WDT - error (when the software is trapped somewhere in its execution).

If the machine is operating already for a long time and nobody touched the PLC program, the is a low probability that it is related to PLC program issue that is causing WDT error.

Another thing that points towards a hardware problem is the message in the HMI: it seems that your HMI is losing communication with PLC at some point. This may happen because the PLC hardware is failing to respond to HMI serial communication.

This "Utility Menu" in HMI is an internal HMI screen like the Control Panel in Windows. Depending on the HMI model it may be accessed by pressing and holding the upper left corner (or the two superior corners at the same time) of the touch screen for some seconds - this is the factory setting. If this procedure doesn't work, it may be that who programmed the HMI changed or disabled the settings for accessing the Utility Menu.

Nevertheless, I recommend to check if the 24V PLC internal power supply is being used to supply power to sensors etc and, if so, check if is there any intermittent short circuit that may cause PLC to go down. In negative case, consider replacing your PLC by a newer model such as FX3U or FX5U (because FX2N is not produced anymore).



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