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Asus RT-AX53U no power and overheating

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    #1

    Asus RT-AX53U no power and overheating

    Hello to everyone! As per subject, I've teared it down and found out that the zone around D1 (central upper part near the PSU connector in the photo below) is almost burning (I'd say the culprit is D1 itself).

    Click image for larger version Name: IMG_20241127_210356.jpg Views: 69 Size: 4.19 MB ID: 3516613

    Could just replacing it solve the issue or am I on the wrong path?
    Thanks in advance for your advices!
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    #2
    The other doubt I have is that usually D stands for diode and it could well be given that there we're likely to be in the power stage but the only marking I can see on the component is 8M and I can't find a diode with such specs..

    Comment

      #3
      I've made a broad research based on that single clue I have (8M) and it could be an 8M Zener diode but they come in many different packages.
      The right one seems to be SOD-123FL but a diode always has the line showing the polarity while this one doesn't... I mean, I read the polarity on the PCB so not an issue and that clue makes me think it could actually be a diode but my doubt is about it actually being an 8M Zener: swapping it with the wrong component would end up with destroying everything (if it isn't the case already).
      At this point, I'm completely lost with no more clues to follow.

      Comment

        #4
        According to this

        https://www.alldatasheet.net/datashe...C/SMZ25B3.html

        datasheet, a valid replacement could be SMZ25B3 but 130V rating seems just a nonsense to me.

        Comment

          #5
          Sometimes TVS diodes can be non-polar. (Actually 2 TVS diodes back to back.)
          OpenBoardView — https://github.com/OpenBoardView/OpenBoardView

          Comment

            #6
            piernov

            First of all, thanks for your follow-up. It should be something polar instead given that on the PCB I can clearly see the polarity indication.
            Apart from this, it stays that just that 8M marking alone doesn't give me a clue about the parameters given that 130V rating is unlikely to be the right guess.
            I'm really clueless and a schematic is unlikely to be found anywhere...

            -EDIT-

            I've taken a look and it seems it could actually be a TVS diode according to its appearance.
            Maybe that "+" marking on the board stays for something else but I still don't know the specs to be able to buy a suitable replacement.

            Comment

              #7
              It is a TVS diode as always being connected between power and ground behind the DC-in jack. (well… when they do put some minimal protection at least)
              It's gonna have a 15V rating or similar to protect from surges above 12V, "BM" markings would match SMBJ15CA, this specific one is from a random Chinese manufacturer (could be https://www.lcsc.com/product-detail/..._C5221618.html for example), but the manufacturer doesn't matter, there are at least a dozen making the same part.
              Silkscreen may not be for the specific part that has been populated, they just used the generic footprint with silkscreen for a standard diode of this package when they designed the board.
              But a polarized TVS diode should work just as well in this orientation, and it could even provide a little bit better protection against reverse polarity of the power input.
              OpenBoardView — https://github.com/OpenBoardView/OpenBoardView

              Comment

                #8
                piernov

                Thank you very much for your help. Precious clarifications!

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