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820-00165 CRAZY NO BACKLIGHT Issue

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  • 820-00165 CRAZY NO BACKLIGHT Issue

    Hi 2Informaticos; team

    No Backlight
    Tested with another known good screen : same
    Display works fine on an external TV through a thunderbolt hdmi adapter

    LCD not detected
    Backlight flashes once when hearing chime

    SMC not talking to the LCD:
    SMBUS_SMC_0_S0_SDA and SMBUS_SMC_0_S0_SCL solid 3.3V

    DP_INT_HPD: 2.67V in diode mode 0.460V

    checked all capacitors and resitances on the LCD path

    EDP_PANEL_PWR: 3.318V and solid just after the chime

    As I've noticed that NO green light and NO keyboard
    So I've suspected the SMC
    Reflowed the SMC: same

    Checked the bios with the Medusa, all the different parameters are looking fine and doesn't make me think about an SPI issue

    I was OUT of Idea; so I took the other issues under consideration first, then I decided to check and focus on the green light
    So I've disconnected the flex LIO board:
    Backlight came back as well as the keyboard. CRAZY

    Replaced both flex and LIO board: same

    So wondering about USB issue shooting down the others signals
    Plugged an USB mouse on the Motherboard USB port with the Flex disconnected : NO Activity

    So now should I focus more on the USB Level or more on J9500?

    Best Regards

  • #2
    "Replaced both flex and LIO board: same"
    Looks like bad LIO connector (J9500) on the MLB.
    Inspect it under microscope.
    Check SMC_LID voltage w/ and w/o LIO flex connected.
    If it goes down, TP/KB is disabled.
    Be sure R5171 is OK.

    Of course, do NOT use Magsafe adaptor 1-->2!!!


    • #3
      Of course, do NOT use Magsafe adaptor 1-->2!!!:
      YES SURE, I only une official 85W cables (magesafe 1 and 2 ) connected to Lab Power Supply

      SMC_BC_ACOK: 3.387V
      SYS_ONEWIRE: wave with peak to peak : 1.50V it should be 3.3V no?
      Adapter sense: 1.5V also

      Strange no? knowing that I already tried another Flex and LIO board.
      What could create that drop of half of voltage....hummmm?

      I'll try to run a wire directly from SYS_ONEWIRE of LIO to the test point near the SMC

      Adapter Sense
      Adapter sense.jpg




      • #4
        If the signal (1-wire protocol) is the same on both lines, U6900 (from LIO board) works.
        You must get aprox 3V DC on multimeter.

        "Check SMC_LID voltage w/ and w/o LIO flex connected.
        If it goes down, TP/KB is disabled.
        Be sure R5171 is OK."


        • #5
          R5171 : 100KOhms OK

          SMC LID with out flex: 3.38V

          SMC LID with flex connected strange wave form:

          SMC LID.jpg


          • #6
            Sounds like broken traces from corrosion on J9500 or crap under it.


            • #7
              If you already tested known working LIO board/flex, then J9500 has something bad there...


              • #8
                I've forgot to mention that I saw minor corrosion at J9500 between pin4 and 10, that of course I've cleaned and quickly re heated.
                Maybe invisible crap under it... Will pass it in the UC, if not successfull replace J9500.
                What do you think ?


                • #9
                  Replacing is not a bad idea. Those pins being corroded always causes issues make SURE the pins of the connector are soldered properly.


                  • #10
                    If is only one line problem (like SMC_LID), you can cut it off from J9500 and bypass with direct wire between MLB and LIO board.


                    • #11
                      Replaced LIO j9500 Connector: Problem Fixed

                      Backlight, Green/Orange Led, keyboard, Sound, USB Port ALL OK

                      Thanks 2Informaticos
                      You can set this topic as RESOLVED

                      Best Regards


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