A1990 ppbus_g3h shorted QA340 (Did i mess up?)

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  • EsIstSimon
    New Member
    • Feb 2022
    • 4
    • Germany
    #1

    A1990 ppbus_g3h shorted QA340 (Did i mess up?)

    Hey there, i got a little question for you guys =)

    i bought a broken A1990 with a shorted ppbus_g3h (5V, 0.045ma, 0.5ohms on ppbus_g3h).
    I found that QA340 (gpu phase 3) was the issue and validated it by lifting LA340.

    The short was gone.
    I wanted to see, if the A1990 would draw 20V again, so i plugged the USB-C in and yes: 20V indeed.
    I wanted to see how the Macbook would behave in this state, so i put the motherboard back inside the case and attached everything.
    Plugged in the USB-C again and... i was back to 5V, 0.045ma. ppbus_g3h shorted again with now 10ohms.
    For now i only checked ppbus_g3h to ground and ppbus_g3h to the inductors of the cpu / gpu. LA650 now has the the same reading(10 ohms), so it seems like QA650 has blown!?

    I am not very experienced, but i was sure that i would not blow anything with attaching power to the machine in this state.

    So i was hoping anyone could give me advice on this.
    Was this expected behavior or just coincidence?

    Thanks in advance :-*
    Last edited by EsIstSimon; 01-24-2023, 10:57 AM.
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