Chosen Solution
I have an old macbook 5.1 A1181 that had some water damage to the keyboard. The keyboard and trackpad do not work , but the power button still does. I have inspected the logic board and removed the corrosion. There was not a lot there but a little. I can obviously use an external keyboard and mouse but would like to use the topcase ones. I am wondering that if there was a short that hapenned would the power button not work also? Or can it be an isolated short that just nuked the usb bus for the keyboard?
I would try reseating the top case to logic board cable, making sure there is no corrosion on the cables end. But first, try that external keyboard to make sure the problem is localized to the top case.
I have inspected the socket that the topcase connects to. The top left most solder joint appears void of solder. Do you know what this connection is?
I had a problem with a gradually declining response from my trackpad (MBP mid 2009), when physically clicking it. It eventually stopped responding completely. This is ok, but makes dragging files very hard. As the children previously used the laptop for watching comics etc, there was a chanse there might have been some liquid spilled on the trackpad at some instance, I started by adjusting the screw under the trackpad. This did nothing, it just changed the click from loose to firm. I then went “all in”. I removed the entire trackpad and found the “clicker”. A small disc that i mounted over a PCB contact. This disc i covered by an adhesive that is perforated around the margins of the disc. I took a sharp blade and peeled it of. What did I find? CORROSION. I cleaned it THOROUGHLY with rubbing alcohol to get all the corrosion of there. Then I put everything back as it was - and it worked as if new again. I have a picture of this but nowhere to post it. This is the fix for unresponsive trackpads!
