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820-00281: No image on display. External works

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  • 820-00281: No image on display. External works

    Hello gents.

    Got a board that originally came in for power failure. Found two caps that were lifted off their pads. This restore power once resoldered. But I’m not getting any image on the display. I do however get video via the usb-c to hdmi to external display

    I’ve got the below measurements:

    PPVIN_S0SW_LCDBKLT_R: 12v
    PPVIN_S0SW_LCDBKLT: 0v
    EDP_BKLT_EN: 0v

    I’m waiting on a donor board to arrive and I was going to replace U9800, but wanted to see if you all had any other suggestions. Thanks.

  • #2
    Any liquid sign on backlight area, or LCD connector?
    Do you get image, only missing backlight?

    Check in the first moments if U8500/01 get output voltage; at least 1-2s pulse...

    Comment


    • #3
      Also have you tried a known good screen?

      Comment


      • #4
        Sorry for the late response

        U8500/01 is 5v
        U8500/05 is 5v

        No image on the screen at all.

        And yes, known good screen. Confirmed with another board that the screen was good.

        Comment


        • #5
          "U8500/01 is 5v
          U8500/05 is 5v"
          I do NOT really know how to interpret this...
          U8501 doesn't have any pin connected to 5V!!!

          BTW, U8500/01 means U8500 AND U8501...
          Both chips have the output on pin 5.

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          • #6
            Yeah was wondering if it was a typo as pin 1 of u8500 was an input pin hence why I included pin 5s reading. Sorry bout that.

            Anyway, U8501 pin5 is 3.3v
            U8500 pin5 is 5v

            Comment


            • #7
              Are these stable voltages?
              Check them with LCD connected.
              If yes, DP_INT_HPD should be high too.

              Comment


              • #8
                Yes they are all stable and all measurements were taken with the display connected. I’ll get the measurement later today, running out of town for a bit.

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                • #9
                  So with display connected, DP_INT_HPD is 3.3v approx.

                  Comment


                  • #10
                    Then you should have image at least, on internal LCD.
                    Try replacing U9850...

                    Comment


                    • #11
                      I have a donor board coming in next week. I'll let you know the outcome once swapped.

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                      • #12
                        U9850 doesn't have board specific firmware.
                        You can use new one.

                        Comment


                        • #13
                          Finally got the chip and replaced. Still no video on display.

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                          • #14
                            Should I go ahead and replace U9800 or are there other items that could be causing EDP_BKLT_EN to be 0v?

                            Comment


                            • #15
                              U9800 supposed to have firmware; try to replace it.

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