Trying to tell you exactly what chip needing replacing is toooo vast! It could be the chip, resistors ,caps or inductors or even shorted traces that require jumps. You need to search the net for boardview and schematic for your board and check for short to ground with multimeter youtube can help if you look right. No light on the magsafe usually means the one wire over voltage is not working , feel around on the board and see also if there is area that is super super hot obviously this means the circuit is shorted. That's all I can do this is a very simple answer to a very in depth answer. Good luck!