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820-3476 video problem. common problem?

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  • 820-3476 video problem. common problem?

    I have two A1502 came in today, identical machines with 820-3476 boards.


    problems are the same, machine can power on, chime , back light will be on (after it chimes and wait like 20 seconds later). sometimes no back light but still chime.

    if it has back light, then that's it, no flashing folder, or apple logo, just black screen with back light ( just like usually we see it boots up but no apple in the middle)

    remove SSDs, and tried other screen tops , still same story.this problem is pretty similar to the 820-3332 board with the soldering problem of U8900
    ( Which Duke figured out and let me say that was absolutely brilliant !! )

    so tried to compare that with this board, but pretty much have no clue, maybe not related. anyone seen similar stuffs?

  • #2
    Not common. What is the history on this? PRAM reset?

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    • #3
      yea already tried PRAM reset.
      history of board, customer sent in entire machine, said just happen one day , no liquid spilled, it's a bit dusty as we see here, but can't find liquid spilled

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      • #4
        External video? Disconnect LCD.

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        • #5
          external shows nothing. I also notice something, when back light is not present, what's missing to boost the circuit is the BKLT_EN_R
          which comes from U8330.
          then what's missing for u8330 to output BKLT_EN_R is EDP_BKLT_EN (0v? close to) ,which comes from the CPU.....

          not sure if Im thinking the right way though

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          • #6
            You 100% sure tried a known good LCD?

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            • #7
              yes sir, I swapped it with another screen top already and still same thing. and if it's just the screen,external should post as well...

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              • #8
                I have no idea. Checked SMC_LID?

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                • #9
                  SMC_LID is high 3. something so it's good.
                  one of the customers agreed to replace the whole board by paying extra. replaced one board today and all good,so it's not the display. and having the other one left now ( had two came in and same issues)
                  I will try my best if found any cure will report back.

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                  • #10
                    I would check the caps and resistors in the eDP lines to the LCD. Damaged connector also possible.

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