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820-3115-B No Light slow buzz...

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  • 820-3115-B No Light slow buzz...

    Hello guys, this is my first topic here and I need some help, I am not an advanced technician but I try all my best to learn everyday ...
    So I have an Macbook A1278, board code 820-3115-B, and I have no light on charger and I can hear a slight buzzing noise coming from the board.
    I have 17V on F6905 .
    But I don`t know where is coming from the slow buzzing noise, I can hear it only if I close the board to the ear.
    What should I check for the first steps?

    This is a very nice forum and I hope I will get the help here.

    Thanks

  • #2
    Post voltage for L6995 and L7030.

    Comment


    • #3
      On L6995 0 and L7030 0.64v

      Comment


      • #4
        Now post resistance to ground (diode mode) on same points.

        Next, post voltages for ISL6259; pins 1, 2, 3, 9, 12, 13, 14, 15, 19, 20.

        Comment


        • #5
          L6995 shows continuity both, on L7030 OL

          For ISL6259 shows:

          pin 1 0.01v
          pin 2 16.85v
          pin 3 4.01v
          pin 9 0.02v
          pin 12 0.00v
          pin 13 0.00v
          pin 14 0.00v
          pin 15 0.00v
          pin 19 5.08v
          pin 20 5.06v

          Comment


          • #6
            "L6995 shows continuity both"
            Do you mean short (000) to ground?
            Post exact value, on diode mode (red probe to ground) and 200 ohm scale too.

            "on L7030 OL"
            Maybe with black probe to ground; and viceversa?

            "pin 12 0.00v"
            This confirm missing 3V42; a short there is a good reason.
            If yes, lift L6995 and see where the short remains.

            Comment


            • #7
              Hello, glad that the forum is back.
              Yes on L6995 is showing short to ground on both, at 200 ohm shows 02.0 on both
              On L7030 with the black probe on ground in diode mode shows OL on red probe on ground shows short to ground on both sides

              Comment


              • #8
                Did you really measure continuity without any power?
                I hope you've removed both charger and battery...

                Comment


                • #9
                  I have removed the power

                  Comment


                  • #10
                    "On L7030 with the black probe on ground in diode mode shows OL on red probe on ground shows short to ground on both sides"
                    Then how do you get these values?
                    You cannot get open line and short at same time, in the same point; no matter if probes are inverted.

                    Comment


                    • #11
                      Sorry It was just an confusion, so with the red probe to the ground on L7030 I get 450 both sides

                      Comment


                      • #12
                        How could you get different values in both sides of a coil?
                        Is just a coil, don't make measurements without logic.
                        .450 is a correct value.
                        You should get aprox 12v on L7030 now.
                        Check resistance between pins 17/18 and 27/28; not to ground...

                        "lift L6995 and see where the short remains."
                        Now your big problem is to find that short.
                        Try to inject tension with bench power supply.
                        Start with 1V and go up, no more than 4V, maintaining current bellow ampers limit...

                        Comment


                        • #13
                          As I said I am an beginner and I try all my best learn every day.
                          Will you be able to explain me better how to inject tension to the motherboard?
                          I have an dc power supply but I need some more guidance.

                          I hope you understand and I really appreciate your good wok here.

                          Comment


                          • #14
                            Do first whay I mentioned before.
                            See where the short remains...

                            Comment

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