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820-2936 screen changing colors

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  • 820-2936 screen changing colors

    Have a 820-2936 with no liquid or drop damage. When turned on the screen just changes solid full screen colors from red, green, blue, gray e.t.c

    Could this be BIOS, PCH, or SMC issue? Never seen this problem before

  • #2
    LCD went in test mode.
    Try few times PRAM reset first.
    If no change, test with known good screen.

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    • #3
      pram reset had no change.

      with known good lcd the screen boots up white like normal but no apple logo with hard drive installed and no question mark folder ever appears without hard drive plugged in, just a blank white screen

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      • #4
        do you have question folder on external??? Voltages on J9000 pins 2 and 4??

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        • #5
          "Pure" white usually means no 3V for TFT matrix; check for 3V at pins 2/3 of J9000.
          Also check external video, as above mentioned...

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          • #6
            pin 2 3.242 V

            pin 3 3.240V

            nothing on external with board running for 5 minutes

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            • #7
              no question mark or activity of any type on external

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              • #8
                Try external monitor with internal LCD disconnected.
                Do you get chime?
                Can you confirm USB activity?

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                • #9
                  I get chime with or without internal lcd however i only get question mark folder on external monitor. I get chime with or without external

                  Yes I have usb activity

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                  • #10
                    If connect original LCD assembly color test comes back?
                    Check continuity for all LVDS data lines of J9000.
                    Pay atention to L9080...

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                    • #11
                      board is in perfect shape with no drop or liquid damage, not sure how this could be a continuity problem.

                      Replaced L9080 L9004 and U9000 and still no question mark on good test lcd. Original screen is still going into test mode.

                      what else can I try?

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                      • #12
                        Try BIOS, just in case...

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                        • #13
                          Applied some heat to PCH and now its shorted. Will update after its replaced.

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                          • #14
                            Don't forget, new PCH requires clean ME region in BIOS!

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                            • #15
                              Just before I changed PCH checked for short one last time and it was gone somehow so tried new bios with new ME region. Now it chimes but cant get original lcd or test lcd to work.

                              Anything else to try or check or should PCH be replaced next?

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