Backlight Fuse keeps blowing

Discussion in 'MacBook Air' started by Rickkap, Mar 17, 2015.

  1. Rickkap macrumors member

    Joined:
    Mar 17, 2015
    #1
    Hello,

    I have a friends A1370 MBA with a backlight blown fuse issue. Without me touching the fuse, everything works and displays on an external monitor no problems.

    I changed the fuse yesterday, but that didn't solve the problem. The external display showed the apple logo with the loader bar underneath it. when the bar got to half way loading the fan started spinning very fast and the eventually blew the fuse again. I'm not sure if this was coincident.

    I took some measurement before the fuse blew again:

    fuse 8v

    3&4 of J9000 = 0v

    Q9706 Pin 3&4 = 8v , Pin 1,2,5,6 = 0v

    I'm not sure what to check next, any help would be appreciated.
     
  2. Mrbobb macrumors 601

    Joined:
    Aug 27, 2012
    #2
    So you have a short. The fuse is doing its job, you must fix the short.
     
  3. Rickkap thread starter macrumors member

    Joined:
    Mar 17, 2015
    #3
    Hi

    Yes I know it's a short but not sure where it could be. I've checked for a short with the fuse out, but nothing.

    I think it might have something to do with the screen inverter, but not sure.

    The thing that get's me is all works well without the fuse, apart from the backlight, but as soon as the fuse is in the fan run's at full speed.

    Also if it was a direct short the surely the fuse would 'pop' straight away??
     
  4. dyt1983, Mar 17, 2015
    Last edited: Jun 2, 2015

    dyt1983 macrumors 65816

    Joined:
    May 6, 2014
    Location:
    USA USA USA
    #4
    edit: To remove personally identifying information not relevant to the thread.
     
  5. Mrbobb macrumors 601

    Joined:
    Aug 27, 2012
    #5
    OK so it's not a complete zero ohms, as the other guy says something that's sucking more power than designed and the system pops the fuse to avoid dangerous condition.

    The fans coming on strong then a shutdown typically means it's sensing run-away temperature.

    To me the only thing that powers the backlit is the inverter, I don't know what else is there, am not an Apple tech. eBay sells lots of Mac inverters.
     

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