Chosen Solution
I have tried all the procedures indicated in most of the Forums and the computer does not turn on. The Magsafe light is not solid green. The problem might be in the proper logic board or in Magsafe DC in-board. In order to test whats is happening, you should disassembly the logic board. Before installing the motherboard back into the case and connecting anything, plug in the AC adapter into the MagSafe board. The LED on the power plug has to turn on and remain solid green. If the LED lights up, you can continue assembling back all the components. If the LED doesn’t turn on, try reconnecting the MagSave board to the motherboard and test again. If still there is no LED light, it’s possible the MagSafe board was damaged and has to be replaced.
Any other suggestions about how to test the Logic Board and the Mag-Safe Board?
Did you spill something on it and short out the keyboard? If so you need to replace it. This is for the 2010 but will show you how: MacBook Pro 13" Unibody Mid 2010 Keyboard Replacement
Other than the MageSafe connector LED there is no other diagnostics to prove the system is able to get power. Are you sure the MageSafe power adapter is good? Is the battery charged (using a second system if you can)? Sometimes it’s a matter of tracing out the power feeds to see whats happening. Using a multimeter you should be able to trace out the power from your MagSafe connection to your logic board. Are you able to do that? Often times I need to replace the MagSafe DC-In board unit as the contacts are worn or damaged. Here’s the IFIXIT guide: MacBook Pro 13" Unibody Mid 2012 MagSafe DC-In Board Replacement
