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820-3476-A chime no image, crazy fan spin

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  • 820-3476-A chime no image, crazy fan spin

    hi, got a 280-3476-A with no liquid damage and reportedly never dropped. i got chime but no image (not backlight problem) not even on hdmi. after a while of being turned on the fan spins like crazy, i never had this behaviour before so what should i look for?

  • #2
    Confirm to have USB activity; just to assure board is not stuck after chime...

    "no image (not backlight problem)"
    So you get backlight?
    Black, or white screen then?

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    • #3
      no backlight problem as no image at all,

      caps lock does not go green when pressed, external mouse light comes on

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      • #4
        Always better to check USB activity using USB OSX pendrive with link LED; if flashes, 100% board is booting.

        Assuming USB activity, post voltages of J8300, pins 9 & 28-30.

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        • #5
          pin 9 0.24v without lcd conmected. 0v with lcd connected
          pin 28/29/30 5v without lcd connected 1.8v with lcd connected

          this with 2 different assemblies



          blinking light on external hdd with osx installed

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          • #6
            Pins 28-30 should get 5v at least first few seconds (even without LCD), when power on the board.
            At same time pin9 should go to 2.5V; 5V will drop if not.
            Post voltage at both pins of L8300, with LCD connected...

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            • #7
              L8300 1.79 v before and after with the lcd connected
              pin9 0 volt with lcd connected

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              • #8
                Post now U8300 voltages.
                If it gets 5V at pins 1 & 3 and 3V at pin 2, you should get 5V at pin 5 too...

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                • #9
                  u8300
                  pin 1 5v
                  pin 2 0v <--
                  pin 3/ 4 5v
                  pin 6 1.78v
                  pin 7 0v

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                  • #10
                    "pin 28/29/30 5v without lcd connected"
                    Check that again.
                    Impossible to get 5V output if enable pin is low; unless U8300 is bad.
                    Better to change U8300...

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                    • #11
                      pin1 5,13v
                      pin2 0v
                      pin3 5,13v
                      pin5 1.78v
                      pin7 0v

                      yeah u8300 probably dead

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                      • #12
                        bypassed it for testing and screen turn on. gonna order one. meanwhile i have to solve the crazy fan spin thing

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                        • #13
                          installed one rom another board temporary and it works. does the fan go crazy if no trackpad is connected? because his own is extremely water damaged

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                          • #14
                            Of course; palm rest sensor is not detected...

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                            • #15
                              all right. will order one

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