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A1990 won't turn on.

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    #1

    A1990 won't turn on.

    Hi, I'm working on an A1990 820-01041-A macbook pro. 5.10V, 0.02A on USB-C meter. PPBUS_G3H seems to be shorted, 0.8ohm across C3501.
    This is my first touchbar repair and I know that the ISL9240 is very difficult, if not impossible to find so I want to be very careful. I used voltage injection to locate shorts before but I just want to make sure that this is a good method for this model macbook. What is the maximum voltage/current I should use? Is it a good idea to remove F7000 and F7001 and test for short again to see if the short is on PPVBAT_G3H_CHGR_REG?
    Last edited by MicroSMD Lab; 10-02-2020, 07:11 PM.
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    #2
    Re: A1990 won't turn on.

    Oh, and I forgot to mention, no physical damage observed, no corrosion. I checked all the large inductors and the only ones that were low ohms were L7330 (15.3ohm) and L7420 (5ohm) but both are CPU lines so I'm thinking these values are not unusual.

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      #3
      Re: A1990 won't turn on.

      Always start at 1V, limiting current isn't really needed, make sure no large BGA is heating up, increase voltage if you can't find anything heating up.
      Yes you can isolate the circuit by removing F7000 and F7001. It's very likely that the short to ground is on the system side.
      OpenBoardView — https://github.com/OpenBoardView/OpenBoardView

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        #4
        Re: A1990 won't turn on.

        Ok, so reading another thread about troubleshooting a short on PPBUS_G3H, I saw that you recommended testing inductors against PPBUS_G3H.
        Doing this I got L7420 = 5.7ohm (PPVCCGT_CPU_PH2), LA340 = 3ohm (PPVCORE_S0_GFX_PH3) which are 1.5V and 1.0V respectively. Since PPBUS_G3H is a 0.8ohm short I'm thinking it's safe to go ahead with the voltage injection but I just want to be sure.
        I'm thinking that since my short is very low that this may not be necessary but I still have a lot to learn so my level of uncertainty is high...lol.

        Comment

          #5
          Re: A1990 won't turn on.

          Yes with a 0.8ohm short to ground it's unlikely that there is a high-side MOSFET shorted. On this board, there shouldn't be any power rail with this low resistance to ground. On some other boards (like with 1000-series or newer NVidia GPU) it could be the case so you always have to be careful.
          So always start with 1V and check if any BGA die warm up. If one of them is warming up stop injecting voltage and find the shorted high-side MOSFET.
          OpenBoardView — https://github.com/OpenBoardView/OpenBoardView

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            #6
            Re: A1990 won't turn on.

            Voltage injection went well, I started at 2A then 3 then 4. I was able to feel a little warmth at 4A after 5-6 secs. C9081 was shorted. There was a little corrosion which I missed because that was the only area of the board that had a little dust and I did not clean it.
            Replaced the Capacitor and the board seems to be booting, 19.7V and current made it up to 1.4A then leveled around 870mA. When I put the board in the machine and connected everything it did not boot, the current leveled out to 30mA, voltage was still 19.7V.
            I disconnected everything and tested the board outside again and it leveled out to 870mA again. Put it back in, connected everything one by one and tested, got fanspin and current peaked around 1.4A, leveled around 900mA then dropped a little lower, fanspin was continuous up to the LCD connection which I did last, then no fanspin, current went to >1A then leveled out to 30mA.
            I did not use the LCD bracket, not sure it that is an issue.
            I looked at a video where Paul Daniels said some of the LCD cables were problematic.
            I don't have USB C to HDMI so I can't test with external monitor at the moment.
            Last edited by MicroSMD Lab; 10-07-2020, 05:31 PM. Reason: Forgot some information

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              #7
              Re: A1990 won't turn on.

              Ok finally got my USB C hub and the system boots fine with an external display. I checked the LCD daughter board but no physical damage. Didn't remove the LCD connector from the logic board side yet, hopefully the issue is there. If not, I'm not sure where to start looking.

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                #8
                Re: A1990 won't turn on.

                Ok, so I removed the LCD connector from the logic board and no signs of physical damage. I did diode mode checks on the pins and the only ones that stood out are 10, 16 and 43 which read OL and of course pin 14 but that's unconnected. I'm thinking pin 10 should be OL but I'm not sure about pins 16 and 43. If this is similar to iPhones in any way, maybe the face time camera could be faulty? Not sure how to move forward.

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                  #9
                  Re: A1990 won't turn on.

                  Well after doing diode mode readings on the LCD, I was satisfied enough that it had to be something that would only show up with the both parts connected (LCD to Logic board) then I wondered if I needed to have the lid open. Now I feel so dumb.
                  System boots fine. Thanks for all the help as usual piernov and I always take no response from you as "you need to give me more to work with" so I keep digging.

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