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iMac a1419 820-3478-a no backlight

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    iMac a1419 820-3478-a no backlight

    iMac a1419 I have the dark screen and the apple that you see with a flashlight pointed at it I have replaced the display connector various components but the screen is always black I understand that the black display connector does not reach voltage help me please

    #2
    Re: iMac a1419 820-3478-a no backlight

    Hi. Are you still trying to repair this display?

    If yes, share quality and detailed pictures of your display. Including the labels on the back side of the display.

    Believe that you will have an aluminum shield with black tape and metal foil tape covering a logic board on the display along with a few screws.

    This is called the T-Con board. Carefully remove the shield and share the pictures of the t-con board.

    Before doing this, what is the history of when and why this screen went dark?

    Confirm the back light connectors are not broken off the display. This the multiple black wire cluster from the imac. It mates with the display and fans out to drive usually 2 led strips.

    If ok, issue could be the inverter power supply or the T-Con board itself.

    We have repaired a few similar units in the past few weeks. Your issues may be similar.

    T-Con boards can be replaced or repaired. Inverter boards are usually replaced.

    Do you have a meter with capacitance checking?

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      #3
      Re: iMac a1419 820-3478-a no backlight

      On this machine backlight driver circuit is on the main logic board.
      T-Con is unrelated to the issue since image is present.

      First thing would be to try another display assembly if possible as a LED could be dead. Next would be measuring voltage on backlight circuit output, which is a bit tricky because it has to be measured across each pair of J8320 with the LCD connected and the board turned on.
      OpenBoardView — https://github.com/OpenBoardView/OpenBoardView

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        #4
        Re: iMac a1419 820-3478-a no backlight

        @piernov - thanks! very nice to know.

        As noted in another thread, we have stumbled across a nice shop on Aliexpress (MACSCREEN STORE) who has low cost stand alone tools to diagnose such panels and also replacement t-con boards.

        They do not sell the backlight strips but they are available from other similar stores.

        Are public schematics available for the main imac power supply and/or inverter boards used on A1312 or similar?

        Learning as we go and wish to diagnose some of these bad boys. Thanks again!

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