I'm working on fixing an HP laptop that I got for free. I have a power adapter that I know works but I'm still unable to get any power where I've tested on the motherboard. With the power jack disconnected I checked the resistance of the positive and negative pins on the motherboard and it is approximately 640 ohms. Is this what it is supposed to be or is there a short in there? Also, is there a quick way to look this sort of information up in the future?