First of all, after we disassemble the laptop and get to the motherboard, need to carefully visually examine it for oxides, darkened areas, traces of soldering, carbon deposits, PCB swelling and other damage, just as carefully inspect all the connectors to make sure that nowhere short or damage.
For example, oxidation in any area, then you need to remove everything and thoroughly clean the board, for example, I wash it under water with a toothbrush, and then blow out all the water from the board (especially from under the chips) with the help of a compressed air containers, we dry it thoroughly,
If we did not find anything suspicious on the board, then it is worth checking for a short circuit on the motherboard, if we don't know the motherboard circuits design, then it is better to download the circuit diagram/ Schematic using the laptop motherboard part number not with Laptop model number. ( see this article how to find the part number )
For example, oxidation in any area, then you need to remove everything and thoroughly clean the board, for example, I wash it under water with a toothbrush, and then blow out all the water from the board (especially from under the chips) with the help of a compressed air containers, we dry it thoroughly,
If we did not find anything suspicious on the board, then it is worth checking for a short circuit on the motherboard, if we don't know the motherboard circuits design, then it is better to download the circuit diagram/ Schematic using the laptop motherboard part number not with Laptop model number. ( see this article how to find the part number )