Refurb / Apple products related / Apple Laptops' Diagnostic techniques, tips, howto Apple laptops' / macOS manual hardware test howto: keyboard, sound, scree
Keyboard test: Open and use the Keyboard Viewerhttps://support.apple.com/kb/PH25242?locale=en_US1. Click the Input menu in the menu bar, then choose Show Keyboard ...
Refurb / Apple products related How to create MacOS installation USB disk.
Use a working MacOS system, download "Disk Drill" from internet and install it. Download MacOS installation application from apple's APP ...