Be aware that the SSD may consume more current than most USB ports are capable of providing and that would explain why the disk is not seen by the computer, or in my case, why the disk disconnects when in heavy usage. My 850 SSD states 1.4A peak current. My USB ports can only provide 900mA. It seems now I need to find out an external closure with two USB 3.0 connections, or maybe get a 3.1/USB-C enclusure and upgrade my Mac. Sorry, not a solution, just more details on the possible issue.

Thank you iFixit for the kit, the Crucial memory modules, and the instructions.

My remarks, repeated in other comments:

- obviously be very very careful with the antenna and the led connector, they are really tiny.

- the board screws are really tight. Had to use some pliers with the torx piece because the iFixit plastic handle did not seem strong enough for the required force. Or better, I had no force to unscrew them using the kit.

- make sure the RAM is fully plugged in. If you can see the coper from the connectors, they’re not well plugged. The machine won’t start if they’re not plugged, not even turn the led on.

- even with the RAM well plugged, the trick to press power for five seconds is needed. Five despairing seconds waiting for the led to come on.

Works perfectly. The kit is perfect. The memories are great. The Mac mini process is quite easy and well designed. I’d say a low end of the moderate.