Before starting this procedure, you must disable your Mac's Auto Boot feature. Auto Boot powers on your Mac when you open the lid, and may be accidentally triggered during disassembly. Use this guide or follow the abbreviated instructions below to disable Auto Boot. This command may not work on all Macs.

Power on your Mac and launch Terminal.

Copy and paste the following command (or type it exactly) into Terminal:

'sudo nvram AutoBoot=%00

Press [return]. If prompted, enter your administrator password and press [return] again. Note: Your return key may also be labeled ⏎ or "enter."

You can now safely power down your Mac and open the bottom case, without it accidentally powering on.

When your repair is complete and your Mac is successfully reassembled, re-enable Auto Boot with the following command (typed into Terminal, as shown above):

sudo nvram AutoBoot=%03