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820-3115 - Hissing/ticking noise by the lvds connector

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  • 820-3115 - Hissing/ticking noise by the lvds connector

    board was liquid damaged. no green light when try i to power it on and Hissing/ticking noise can be heard by the lvds connector.
    SMC was shorted to ground, so i removed and replaced the SMC. but Hissing/ticking noise is still there.

    board now turn on and passed ASD. where is the noise could coming from in that area?

    Last edited by Alan.L; 03-03-2017, 11:09 AM.

  • #2
    Backlight coil, remove backlight fuse and see if noise is gone. Then check all resistors/caps/LP8550. Only mess with this if it really is an issue, I would probably not bother if everything works.


    • #3
      noise is still there after i removed the backlight fuse. noise is not coming from the backlight coil, i can hear the noise below the coil area. it is audible.

      LP8550 area it is all good. i have no problem showing backlight and images on screen.

      also i notice something strange. i have to replug magsafe connector multiple time in order to get a green light. it can charge and detect battery info on OSX fine.
      after i get green light, i can turn on and off and repeat no problem. how i check if i did a good job on SMC? this is actually my first time replacing a smc which seems to be 1st success otherwise...

      PPBUS_G3H =12.52V
      PP3V42_G3H = 3.52v
      PPVRTC_G3H = 3.3v
      PP5V_S5 = 4.93v
      PP3V3_S5 = 3.32v

      3.52v on PP3V42_G3H seems little high than usual.

      Resistance between pin 17/18 and 27/28 of the ISL6259
      4 ohms on pin 17/18
      22 ohms on 27/28


      • #4
        When you get no green light is PPBUS and 3V42 present? I doubt this will be SMC related.


        • #5
          sorry it is actually very dim green light.


          PPBUS_G3H =12.52V and 3V42 = show 3.52v

          i replaced u6990, d6990 before because it had corrosion.
          Last edited by Alan.L; 03-03-2017, 10:22 PM.


          • #6
            The green light issue is probably the magsafe board, swap it with known good one.
            Measure the voltage on pin 1 of R7081 and 7086.


            • #7
              already tried another magsafe board and still same.

              dim green light
              16.05v on pin1 of R7081
              6.80v on pin1 of R7086

              when power on with green light
              6.3v on pin1 of R7081
              6.70v on pin1 of R7086
              Last edited by Alan.L; 03-03-2017, 11:15 PM.


              • #8
                Check resistance across R7081, if it's good replace U7000.


                • #9
                  they are good.

                  i'll have to do it tomorrow. i need to get some sleep. thanks
                  Last edited by Alan.L; 03-03-2017, 11:25 PM.


                  • #10
                    Before touching anything I want to know what voltage is on pin 2 of R7081 when there is no green light. If it also 16V then there is an issue with the U7000 circuit most likely.


                    • #11
                      dim green light.

                      15.92v on pin2 of R7081
                      16.01v on pin1 of R7081

                      with green light.

                      0.019v on pin2 of R7081
                      6.3v on pin1 of R7081

                      i think there is also noise coming from this area as well.
                      maybe i should ultrasonic this board..

                      thanks duke, i;ve catch you tomorrow.
                      Last edited by Alan.L; 03-03-2017, 11:43 PM.


                      • #12
                        Yeah U7000 is not pulling down R7081. This could have a bunch of reasons, a clean would be a good place to start.


                        • #13
                          I have also seen a bad U6990 cause high voltage on pp3v42. It also kept causing R6990 to blow until I replaced U6990.

                          I would compare resistance to ground on pin 1 on C6991 to a known good to make sure it is not partially short, then check R6990 and replace U6990 again just for good measure.


                          • #14
                            ok, i've ultrasonic the board, still no good and noises are still there.

                            i've even replaced u7000. no affect.

                            U6990 had been replaced before. maybe i had a bad one from donor board?

                            R6990 is fine.


                            • #15
                              ok i will replace U6990, Q7030, Q7035 from another donor board.


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