hello there,
look at the vdd-main line diagram (you need a schematic). Start by removing the power supply bridge (R3303). This will solve a lot of your problems. In general, the line is quite straight as like for Apple and you should have no trouble finding the short (use the TP0540 test pad). Anyway, you have got dwo diferent sub-circuits of power supply: The North with all system supplied and The South - just charger with pp_bat and i2c services for main battery. Thats all. More similar casesys you can find on my (free of charge) repair blog. Just read, ask if not understanding and learn. Details can find "about me" tab.
-fingers crossing,