To disconnect the optical drive thermal sensor, pinch its cables between your thumb and a spudger and pry the spudger upward to lift the connector up and out of its socket on the logic board.
To remove the logic board, two cylindrical rods must be inserted into the holes highlighted in red. Inserting instruments into any logic board holes other than the ones highlighted in red may destroy the logic board.
Insert a Mac mini Logic Board Removal Tool into the two holes highlighted in red. Be sure it makes contact with the outer case below the logic board before proceeding.
If you don't have a Logic Board Removal Tool handy, you can use two tools having a maximum diameter of 2.5 mm instead. Just insert one into each of the highlighted holes.
Carefully pull the tool toward the I/O board. The logic board and I/O board assembly should slightly slide out of the outer case.
Cease prying when the I/O board is visibly separated from the outer case. Remove the Mac mini Logic Board Removal tool.
Simultaneously push the two plastic clips on the far left and right sides of the I/O board toward the middle of the I/O board and pull the I/O board away from the outer case.
De-route both antenna cables from the clips securing them to the top side of the logic board.
Be careful when removing the cables from their retaining clips, as the thin metal contacts crimped to the antenna cables can be easily torn off. If any contacts become separated from the antenna cables, use a pair of pliers to gently crimp them back into place.
Pull the I/O bezel away from the logic board, minding any cables that may get caught.
Try not to handle the small steel EMI fingers on the logic board and I/O bezel, as oils from your fingers may cause interference issues. Before installing the logic board assembly, clean the EMI fingers to remove any oils transferred during the removal process.