Xbox One S - 12V Rail Short - Q9F1 Keeps Blowing

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  • grimacelord
    Badcaps Veteran
    • Jan 2017
    • 354
    • USA
    #1

    Xbox One S - 12V Rail Short - Q9F1 Keeps Blowing

    Hello,

    Have an Xbox One S here that has a short on the 12V power rail. There is no power, beep, or partial fan spin when connecting power cable.

    After diagnosing with thermal camera, Q9F1 MOSFET (NTTFS4C50N) is getting hot. When I remove this MOSFET, the short on the 12V rail disappears.

    I first replaced Q9F1 with one from a donor board and then partially reassembled the Xbox to test. When I plugged the power cord in, I got a partial fan spin and I thought I had fixed it, but unfortunately, the Xbox still did not power on. So I then disassembled the Xbox again and found that my newly replaced Q9F1 had blown again. So this time, I used another donor board and replaced Q9F1, Q9F2, and U9F1 which both of the MOSFETs are connected to. I checked to make sure the short on the 12V rail was gone and it was until I connected the Xbox back to power and it blew Q9F1 again.

    What keeps blowing Q9F1? Looks like Pin 5 of Q9F1 is connected to L9F2 which is V_VREG_12P0_MEM_NBCORE and the other side of that inductor is the 12V line coming from the power supply (according to my interpretation of page 50 of the schematic), could the power supply be blowing it?

    Hoping someone could help. Thank you.
    Tags: None
    • grimacelord
      Badcaps Veteran
      • Jan 2017
      • 354
      • USA
      #2
      Well, I decided to test my own theory and use a brand new power supply in case something was weird with the original and even using a new power supply, Q9F1 blew as soon as I connected it to power, so it's not the power supply causing it. Still not sure what to check...

        Comment

        • grimacelord
          Badcaps Veteran
          • Jan 2017
          • 354
          • USA
          #3
          Attached two screenshots from the relevant schematic page.
          Attached Files

            Comment

            • grimacelord
              Badcaps Veteran
              • Jan 2017
              • 354
              • USA
              #4
              Hoping somebody can see what I am working with here because I am really not sure what I need to check for.

                Comment

                • grimacelord
                  Badcaps Veteran
                  • Jan 2017
                  • 354
                  • USA
                  #5
                  Upon further probing, I have found a short on Pin 1 of C9F1 which is V_VTTB. I am reading 0.013V in diode mode and a working Xbox has a diode reading of 0.305V.

                  The only components on that entire V_VTTB line is a whole bunch of resistors and a few capacitors. I removed ALL of the capacitors on that line and it's still shorted to ground. What does that mean? Internal short?

                    Comment

                    • essuman32
                      New Member
                      • Jul 2023
                      • 3
                      • Ghana
                      #6
                      Xbox

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