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Duff FX3G 80MR

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This is just information that might help someone in the future.

I was called to a job where the above PLC had fault lights on. 

When I connected, there was no program inside.??

They had a back-up program so I downloaded it and all seemed OK.

Then the error light started flashing again. Once again, the program was missing.


Short version: They rushed out to buy a new one, I installed it, put the program in and they were back up and running with no issues.


Later, in my office, I opened the PLC to see if there was anything obvious. There wasn't.

If you have ever opened an FX plc - they are a marvel of micro electronics with virtually no replaceable parts. (obviously output relays and transistors but that was not the problem)

I have lots of 2nd hand FX plc's so I swapped out the 1.0Fsupercapacitor from one. More in hope than anything else.

That was the problem - it worked perfectly. A £3 supercapacitor fix. 

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Useful information.

Thank you!

We have replaced Fx3U-MR series output relays 2-3 times without any worries, but most of rest requires more serious soldering equipment such as a microscope, hot air station, low melt, quality flux and other accessories... as well as a steady hand, but so far no we had to.

I have been in this factory for a decade now and we have never had a Melsec main CPU unit fail.

Only one flexo press that gave me trouble was an Fx3u-485ADP-MB, which after 15+ years of faithful service just didn't want to communicate anymore.

There are no alarms in the PLC or errors in the module's special registers and no issue with wiring...
It worked flawlessly on my desk with whatever equipment I could think of that I had available to test it on, but on the machine a beam.

We replaced the adapter 2 times with a brand new one and it stopped communicating after 2-3 months of operation.
Now the third one has been working on the machine for 2 years now, but we have a new spare in the cupboard.
Now I have two that I can use for small projects and R&D with one thing in mind that I don't have to rely on them for serious stuff... :)


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