G3Hot Shorted to Ground

Discussion in 'MacBook Pro' started by bouba148, Aug 21, 2016.

  1. bouba148 macrumors newbie

    Joined:
    Mar 23, 2015
    #1
    Hi All,
    I'm currently trying to repair a 820-2879 Macbook Mother Board and here are the symptoms:

    No Magesafe's green light
    G3Hot (PP3V42_G3H) is shorted to ground
    After removing the Coil L6995 to figure out where is coming from the short, it comes after the Coil : C6999 is also shorted to ground but it is not responsible of that short. So another componant is putting this track to the ground. OK need to find out witch one it is......BUT beside that i've mesured the output of U6990 on pin 4 (P3V42G3H_SW ) without L6995, i should normaly read 3.42V but strangely i'm reading 15.2V????
    Someone of you guys had this problem before? where this 15.2V voltage is coming from? is the U6990 dead?
     

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  2. fixationhub macrumors newbie

    Joined:
    Jul 22, 2016
    Location:
    Georgia
  3. JOHNLAG75, Dec 18, 2016
    Last edited: Dec 21, 2016

    JOHNLAG75 macrumors newbie

    Joined:
    Feb 13, 2015
    Location:
    Greece
    #3
    Hi all
    I have the same issue with a 820-3330 macbook logicboard at the first i find the r6990 47k resistor burn and change it then i connect the magsafe and get green light about 10 sec and the r6990 smoke at this time i get 7.8 volt at pin 1&2 l6995 and not 3.42v i remove the l6995 and i've mesured the output of U6990 on pin 4 P3V42G3H_SW at 15.2V same as you i find l6995 pin2 short to ground and short gone only when i remove the smc.
    I think the u6990 is dead and the overvoltage outpout at u6990 pin6 in my case burn the smc now i wait u6990 and smc from donor logicboard.
    Have solved your?
    Sorry for my english.
     
  4. bouba148 thread starter macrumors newbie

    Joined:
    Mar 23, 2015
    #4
    I, no i haven't solved the problem, but i think to know where is it coming from: i've removed the shorted capacitors and put 3,4 volts and incresed the current after what the gpu became hot, that's why i'm thinking that's the gpu.
     
  5. npreq macrumors member

    npreq

    Joined:
    Nov 23, 2016
  6. JOHNLAG75 macrumors newbie

    Joined:
    Feb 13, 2015
    Location:
    Greece
    #6
    Hi when you say Lewis you mean Luis Rossmann?
     
  7. npreq macrumors member

    npreq

    Joined:
    Nov 23, 2016
    #7
    Yes
     
  8. JOHNLAG75 macrumors newbie

    Joined:
    Feb 13, 2015
    Location:
    Greece
    #8
    Luis time is precious and i think can't answer to everyone question.
     

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