Chosen Solution
The machine was not charging - charger LED remains black when connected to the machine (tried multiple known good chargers). Reset SMC, no change. Disconnected battery and connected a known good battery with some charge. Was able to power on and see battery stats, showed not charging with power adapter connected. Still no LED light on connected chargers, no charge being transmitted. Replaced MagSafe DC-in board with two other DC-in boards, same issue with both. Tested the voltage going through the DC-in board and it gives 19.5 V which is higher than the standard 16.5 V for the MacBook Pro (13-inch, Mid 2012). Could this higher voltage be due to an issue with the logic board? Note that the logic board appears to be clean (no clear signs of corrosion or damage). Thank you for your help! The following image shows the read-out from coconutBattery with a new battery installed and a power adapter connected to the MagSafe board.
OK at this point we know the battery is talking to the logic boards SMC services as the battery info is visible. As you have already replaced the DC-In board and tried a second charger that only leaves one thing left the logic boards one wire connector connection to SMC is not working properly. At this point you need to get deep into the logic boards logic using a schematics and boardview drawings using a DVM to check the pathways. This really needs someone with deeper skills and access to the needed parts.
