Raplaced Logic Board after water damage, Still not powering on

Thanks so much for your response.

I took out the keyboard cable and tryed to jump it. After several attempts (is this normal?) It finally turned on. I ran it for an hour or so, applied updates, restarted; all good. When I tried to repeat my success by shutting it down and jumping it on again, it did turn back on; again, after several contact taps.

I am using a 85w power connector.

I've experienced the need for several taps on the pads on a number of machines, it is not abnormal. It takes a good solid connection between the 2 pads to power it on. There is solder on the pads making the surfaces uneven. To confirm the upper case and/or it's cable is bad, reattach the cable to the logic board and attempt to turn it on using the power button. Make sure the cable is in the ZIF connector all the way and is in it evenly. If it powers on test the keyboard further. If it does not power on, inspect both ends of the cable for burn marks and corrosion. If you find corrosion clean it with isopropyl alcohol and a tooth brush, also clean the ZIF connector on the upper case in the same manner - give it a try. If you find burn marks you can try to clean it with an emery board. Use gentle in-out strokes from the end of the cable. If you go side to side you increase your chances of ripping part of a trace off the cable - give it a try. Upper case is bad if no problems with cable.

On the A1342 the top case cable is tricky to install. Since the ribbon cable is very short it's hard to push it completely in the connector. Here's a method that help to secure the cable in the connector: center the ribbon cable to the connector then enter it a bit inside the connector then stick a piece of scotch tape on the cable to fully penetrate the connector. You may also use scotch tape to remove the ribbon cable from the connector.

@lemerise Great tip!

@ABCellars Connected ribbon and does the same thing. I even reconnected after I jumped w/o, and about half the keys actually respond.

I'm guessing this means I need a new upper case.

Unfortunately, your guess is correct, you will need a new upper case. On the good side you learned a little bit about how to troubleshoot the problem and confirmed that your new logic board is in working order. With part of your keys responding that confirms that the cable was in the socket correctly. When I first answered this I was not sure if the cable was in correctly or that your replacement motherboard was good. After you established the logic board was good, that is why I had you double check the cable. It would have been a shame to have replaced the upper case over a bad cable connection.