820-3330b board with no image

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  • hypergl
    Member
    • Jan 2022
    • 14
    • Slovenia

    #1

    820-3330b board with no image

    Hello everyone.

    My own macbook pro from 2012 just decided it had enough. There is no image on the screen (screen dead, no backlight, no image whatsoever even with a torch behind the apple logo), there is no image on external via thunderbolt/DP adapter.

    There is chime though, there is also all the controls from the keyboard, so it is possible to control the backlighting of the keys.

    I had problems for the past year or two with the display, showing a green line (single pixel) or two, maybe three. But nothing that I took seriously as I had always used an external display.

    The computer is mine since new, I got it with the optional "hires" matte screen.
    Never seen water, always took good care of. A few scratches on the case, no dents, no serious damage.

    So as I was probing the motherboard for voltages it happened that the display got turned up, showing the logo and I got the folder icon (because I removed the SSD), tried to turn off and on a few times, the display lit up like new most of times, the fourth time then it went dead again.

    So the board is not to throw away yet.

    I checked the LVDS connector and i got on the following pins:

    1 - GND
    2+3 - PP3v3_SW_LCD - 0volt (expected 3.3volt)
    4 - PP3v3_S0 - 3.3volt
    5 - NC
    6 - LVDS_DDC_CLK - 3.3volt
    7 - LVDS_DDC_DATA - 3.3volt
    8+9 - LVDS_CON_A_DATA - 0.3volt
    ...
    21 - LVDS_CON_B_DATA - 0.3volt
    ...
    31 to 36 - LED_RET - 0volt (expected 0.5volt)
    ...
    38 to 40 - PPVOut_S0_LCDBKLT - 0v

    I also checked on the U9000 and got this on the following pins:

    1 - 0volt (expected 3.3volt)
    2+3 - 3.3volt
    4+5 - 0volt (expected 3.3volt)
    6+7 - GND

    What should I check next? Can you give me any hint? I really don't want to give up on this machine, it served me well and I am sure it could serve me for at least for another two or three years.

    Thanks in advance...

    Martin
  • mon2
    Badcaps Legend
    • Dec 2019
    • 13999
    • Canada

    #2
    Re: 820-3330b board with no image

    Hi.

    The enable for your LCD panel is off (pin # 1 of U9000). See attached.

    Post the voltage readings for the MUX selector circuit.

    Next,

    Guessing some power rail may be failing. Start with removing all power / no battery.

    Meter in resistance mode (2k scale). Check and post the resistance to ground of each and every coil. Each coil is linked to bulk caps and a power supply rail. You may be borderline facing a bad cap on one of these rails. Checking for a very low resistance to ground. CPU rail will be low in resistance by design.
    Attached Files

    Comment

    • hypergl
      Member
      • Jan 2022
      • 14
      • Slovenia

      #3
      Re: 820-3330b board with no image

      Originally posted by mon2
      Guessing some power rail may be failing.
      It might just be, since in the last year I could not power a single optical mouse on one of the two USB ports... Can't remember which one, but will try to...

      Comment

      • hypergl
        Member
        • Jan 2022
        • 14
        • Slovenia

        #4
        Re: 820-3330b board with no image

        So, got a little time today and measured the next things.

        Q9607:

        pin 1 - gnd
        pin 2 - 3.3V
        pin 3 - 3.3V
        pin 4 - gnd
        pin 5 - 0V
        pin 6 - 0V

        R9676

        pin 1 - 3.3V
        pin 2 - 0V

        R9678

        pin 1 - 0V
        pin 2 - 2.6V

        R9671 to R9674

        pin 1 - 3.3V
        pin 2 - 3.3V

        L9621

        pin 1 - 0V
        pin 2 - 3.3V

        Comment

        • hypergl
          Member
          • Jan 2022
          • 14
          • Slovenia

          #5
          Re: 820-3330b board with no image

          Finally I found the problem... It was not a Cap or Coil... It was U8900, so the chip delivering the power to the discrete graphics. Found a script on how to disable the Nvidia graphics and I also set Csrutil to disable. Right now I'm using the laptop only on integrated graphics and it's working just fine. Maybe someday, if I have the need to, will get myself on changing the U8900.
          Thanks guys!

          M

          Comment

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