If you open up your MacBook, you will find the battery next to the motherboard. If you look along the boundary between the two, you will probably find a big square piece of plastic with wires going out of it, to the battery. This will be on the motherboard. Pry up the plug, so that it is disconnected. Then, partially turn your Mac over and try to power it on. This will drain any charge left in the motherboard's capacitors. Your motherboard is now drained of any residual charge and has no power to it.
Of course, this is a most-mac case, as you did not provide any detail. For a more precise answer, could you turn over the Mac and look near the vent at the top of the back case. There is some small text there. Read it and tell us what the model is.
Cheers,
Falcon16