This is part of displayport circuitry. This smoked because of a shorted U3890, which &&^&@@ up everything else on the line. U3890 probably got hit by moisture because it is right by the edge of the machine. Whatever is on that edge is most suspectible to liquid. On 2009/2010 machines it is the onewire circit, poor little U6901's PP3V42_G3H via sits all unprotected in the corner. Here it is even stupider, a higher voltage boost circuit is sitting right on the edge where water goes in. Gotta love Apple. :)
This is pulling down PPBUS_G3H & shorting your 12.6v main power rail of the system to ground which is why it is not turning on.
Remove U3890, U9410, and associated circuitry because it's all probably F'd now. Think of it like an appendix. If you are new to board repair it is best to simply remove this and just forget about displayport and enjoy the working machine.
If you are using cheap junk equipment to remove it it will be miserable. Try to find some used Hakko gear, they just tossed the FR-801 line out the door. I picked a 2nd one up for the shop for $300, not bad at all.
If you are lucky this fixes it, if you are UNLUCKY you have burned CPU power circuitry by U7880. If it went this far, your board is toast. Hopefully your shorts are all in the chips and not in the board, else it goes in the bin.
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