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US5-B5-T24 Snap, Crackle, Pop!


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A bit of a weird situation with the unit in title.  It is installed and working as you would expect (new application, just programmed this week), but I noticed some odd noises coming from it.  I disconnected all the connectors and cables except for the 24VDC supply and it still makes the noise.  When I cycle power to it, it is quiet up until it completely finished booting and then runs the application.  As soon as the application starts running, the unit starts making the crackle sound again.  There are not any relay IO, so it can't be a chattering contact.  It is hard to tell if it is the speaker or something else.  Attached are a couple videos where hopefully you can hear the audio OK.  Any ideas on what it might be?

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  • MVP 2023


This sound like internal DC/DC.
Maybe some broken or not fixed (not glued) ferrite act as sound speaker driven by internal or external power supply current modulated by PLC program cycle.
For recognize it is internal or external modulated current please use another power supply.


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  • MVP 2023

As it is working, I am with Kratmel.  I've had power supplies make very odd noises, but I then don't trust the unit and replace it.  



9 hours ago, Damian said:

(new application, just programmed this week)

Ensure that the installers didn't let any swarf etc into the unit.  I've had many plcs stuffed by "experts" relocating equipment and drilling/cutting holes willy nilly without any covers over all the control gear at all, with subsequent failure.  "Aus, it doesn't work anymore!"  "That's because you are a pack of dills".  I used to work with a PLC brand that came with paper protection all over the vents, explaining about removal after ALL works were finished.  Great idea.

Time to remove a cover to see what is really going on, me thinks.  😨

cheers, Aus

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