iMAC A1418 Backlight issue

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  • roman728
    Member
    • Jul 2018
    • 28
    • Slovakia
    #1

    iMAC A1418 Backlight issue

    Hello friends,

    I have this unit with no backlight on screen. After inspection i determined there is a shorted capacitor on BKL_BOOST circuit. I removed the capacitor, short is gone but backlight still not working. I found that Q9702 is not open and R9721 is only around 70kOhms but according to schematics it should be 301k. I removed the resistor and connected the gate of Q9702 directly to GND. Now i have 12v passing by the mosfet to turn on backlight IC LP8561 (U9700) but BKL_BOOST circuit is not working. I can measure only 12V there but it should be around 60V.

    Can you tell me what to measure next ?

    Schematics can be found here : https://www.badcaps.net/forum/troubl...90#post1031290
    Tags: None
    • FriedFred
      Senior Member
      • May 2024
      • 137
      • Germany
      #2
      I suggest to add those removed, damaged capacitors and not only just remove them. Usually, the boost circuit needs the capacitor to boost an input voltage to a desired output voltage.

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