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820-3662 liquid damaged no power

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  • 820-3662 liquid damaged no power

    Hi All,

    So I have this nice Retina here with liquid damage.
    I cleaned it. Battery is dead.

    It was powering on, but no CPU VCORE.
    I checked the power to U7200 and I saw R7202 was corroded. I changed it and it turned on for a sec or two and turned off.

    PP3V42_G3H was 70-80 Ohm short to ground. I found a bad corroded cap C1950. I changed it with U1950.
    It turned on for a second again. I was able to turn it on with SMC bypass, but after 10 seconds it turned off. Never could turn it back on.

    I found SMC crystal wasn't oscillating and there was no voltage on it. No short! I didn't have the same board so I took the SMC off of the 820-3332.
    After I replaced the SMC the crystal is oscillating, but still not turning on. The fan just barely spins up. This is not a turn on-off loop thing.
    This tries to turn on, turns off and it does not try to turn on again. I tried SMC bypass mode, but same thing. I couldn't find any short.

    It still powers on if I remove R7202, just of course no CPU VCORE.

    Any ideas?

    Thank you!
    Last edited by bighead; 07-05-2016, 03:13 PM.

  • #2
    Start with using the correct SMC. The original one is probably fine, was just crap under it.

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    • #3
      Well, I received the parts board for this board. I changed the SMC with the correct one, but still no power.
      I lifted all CPUVCORE coils at the CPU side and checked them if I have anything on them without connecting it to the CPU.
      With multimeter is show 3V which is extremely high. I checked with scope and it shows the PWM wave on both side of the coils. All of them(3).
      How is that possible?

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