MacBook Pro 13", A1278, Mid 2009, MB990-991LL/A, Board#820-2530-A
This model and the accompanying 15" laptops were the first to incorporate the "non-user serviceable" battery.
Power-on pads are two tiny metal surfaces on MacBook logic boards.
To find the pads for a particular board, enter the year, screen size, and computer type below, and the relevant logic board with power-on pad locations will appear. Click on the images for details and additional pictures.
Please let me know if you find errors, and if you have images of boards not listed, and I will be happy to include them!