hello
i have a mbp a1278 820-3115-b the problem is the machine boots very slowly also the fan are in full speed and the applications take a long time to open .The cpu shows 100% usage inspite of no apps running.I have changed hdd otherwise the machine works normal.where is the problem .i ran istats it did not show me any sensor problem, but i assume some sensors are not reporting well to smc.

You need to use AHT or ASD EFI or ASD OS to ful l checkout sensor and other subsystems on board.
Prior this check the board using microscope. It is possible water damage.

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