Chosen Solution
I picked up a used mid 2012 non retina MBP with the I5 and 4GB of ram. I bought a certified used logic board 820-3115-B and new ram for it. I completed the swap, cleaning, new thermal paste ect and attempted to turn it on. Completely dead. I connected it to wall power and the green light on the plug lit up as well as the green battery indicators on the side. I open the lid and there was nothing from the power button. Closed the lid and heard the mechanical noise from the cd player centering itself. Opened the lid again and it eventually booted up but the keyboard was unresponsive. Shutdown and checked all the connectors. the keyboard cable was not seated entirely. reseated the cable and tried again. The keyboard backlight comes on but it won’t boot anymore. Also, when the lid is open the “sleep mode” light on the front slowly flashes and goes solid when I close the lid. Any Ideas?
try starting the system with the keyboard ribbon cable unplugged using the power-on pads on the logic board and see if works properly with an external keyboard. If it does, you will most likely need to replace the internal keyboard or the entire top case.
