Try a new DC jack to eliminate this being the cause. Grab a schematic and board view for 820-2936, and measure the power rails PPBUS_G3H and PP3V42_G3H. If these are lower than it says in the schematic, or not present, you need to investigate this further. Feel U7000 (charging IC) to see if it is getting hot, this can sometimes short to ground.
Beyond this, check the board for any brown probe points (indicates cleaned liquid damaged). I assume you have plugged it in without the battery connected too?