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Two of our Unitronics PLCs V350 seemingly died. 

For a while the PLCs have been running fine, but after a power outage the PLCs wont start again. 

The power connection is fine supplying 24V, but the PLCs do not start. When power is turned on, nothing at all happens at the screen. I fear they are out of reach.

Is there anything I can do? is there some kind of hard reset or factory reset button? Any ideas are welcome.

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Do the HMI's show anything on them or is it a black screen?

If it's a black screen I suspect the power outage may have taken out the power supply on board.  if you remove the back cover check the on board fuse with a multimeter and see if it's blown.


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More than likely when the power failed there was a surge that damaged something in the controllers power supply stage.  I'd contact your distributor and see if they can help you obtain a new unit, return the existing for evaluation to determine what did happen.

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In case you haven't done so, check the power supply is actually supplying 24v during the plcs trying to run.  And in doing so, disconnect everything else that runs from the same supply.  It might be a short somewhere else that is shutting down the supply.

And a later PS to further explain.  One of the infrequent supply failures I've had over the years gave tiny amounts of 24 out without load, leading one to think that the supply was ok.  Loading it up however, and it dropped right off.  But such behaviour initially points to the supply reacting to a short.  I finally isolated it by trying another supply, that then worked everything perfectly.

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