19v accidentally applied to 12v PCB/board

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  • stormy1777
    Senior Member
    • Oct 2015
    • 137
    • USA
    #1

    19v accidentally applied to 12v PCB/board

    Friends,
    It appears I've accidentally applied 19VDC to a PCB that should only run 12VDC.
    The board now does not power on, even with 12VDC..
    Using a thermal camera shows entire board remains COLD except one component (near power plug) that heats to 120C and higher!!

    Suspected component is marked with "T" (slanted) and "BE", think/hope it is some kind of fuse, in photo just ABOVE the green power terminals and LEFT of the 16V capacitor (on right of photo)

    Interesting part is measuring continuity across that component shows 0-reistance and a BEEP, also same thing happens across the green plastic wire power terminals (bottom of photo).. which is not what i'd expect from a FUSE, as it would CUT power and not ALLOW it to flow...

    So, now writing/thinking... maybe the allowing of current causes the heating, and that's not a FUSE, but a DIODE that is supposed to BLOCK flow, but it got "blown" and now causes a "short - circuit"...

    Now question how to proceed, I have no way to know the exact type/size of Diode.. what if.... I just REMOVE it?? could that cause the circuit to start working again? since it will eliminate the short-circuit and "open up" the board to get power...

    I do not know the board vendor or type it is part of a no-name network/switch.




    Attached Files
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    • stormy1777
      Senior Member
      • Oct 2015
      • 137
      • USA
      #2
      closeup , the heated component is marked "BE" - suspect it is a diode! very tempted to remove entirely, any thoughts welcomed!
      Attached Files

        Comment

        • CapLeaker
          Leaking Member
          • Dec 2014
          • 8146
          • Canada
          #3
          Probably a TVS diode that has a certain voltage rating. If it exceeds the voltage it goes short. Yes if you take that diode out, it should work again, just without protection. The code BE is a Vishay SMBG12CA or an SMAJ12A
          https://www.mouser.ca/ProductDetail/...2BE8RaAQ%3D%3D

          point is: it’s a TVS.
          Last edited by CapLeaker; 07-25-2025, 03:42 AM.

            Comment

            • stormy1777
              Senior Member
              • Oct 2015
              • 137
              • USA
              #4
              Thanks DEAR friend - before seeing your post, could NOT resist the temptation!!

              took soldering iron, removed one side came clean, other side did not heat enough i didn't want to harm other component, so it got "ripped" a little, and device is back fully operational.. incredible!!!
              thanks... never realized diode acts as a fuse learn something new everyday!!


              Click image for larger version Name: image.png Views: 27 Size: 295.9 KB ID: 3690239

                Comment

                • CapLeaker
                  Leaking Member
                  • Dec 2014
                  • 8146
                  • Canada
                  #5
                  No. It doesn't act as a fuse. It just shorts out the voltage rail to ground. It is there to protect the circuit from over voltage condition.

                    Comment

                    • stormy1777
                      Senior Member
                      • Oct 2015
                      • 137
                      • USA
                      #6
                      What is meant they acted similarly, from a FUNCTIONAL point of view (circuit protection), fuse disconnects wire, whereas diode "connected" (short circuit).. always thought only fuse can protect circuit, by cutting power, here, a short-circuit did the trick..

                        Comment

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