On the following sites you will find repair and operating instructions for repairing and maintaining your devices.
Also you can free download all these users guide! These materials are for personal use only.

Manuals for repair of mobile phone
https://www.manuals.co.uk/telephone/mobile-phones
https://www.mobilephone-manualsonline.com/
https://www.mobile-manuals.com/

Laptop Schematic Download
https://www.alisaler.com/
http://kythuatphancung.vn/
http://ufotech.com.vn/forums/
https://laptopblue.vn/
https://www.eserviceinfo.com/
https://www.laboneinside.com/
http://schematic-x.blogspot.com/p/schematics-download.html
https://www.notebook-driver.com/
https://www.driverscape.com/

iPhone, iPad, MacBook circuit diagram
https://pakfones.com/iphone-6-schematics-diagram-pdf-all-pages-and-components-searchable/
https://www.apple-schematic.se/board-category/macbook-air/
https://www.gadget-manual.com/apple/

Samsung Electronics Service Manual (Laptop Circuit Diagram & Manual)
https://www.manualslib.com/brand/samsung/
https://www.martview-forum.com/forums/all-hardware-schematics-by-various-brand.240/
https://www.mobilephone-manualsonline.com/samsung/samsung-pdf-schematics-and-diagrams/
https://www.mobile-manuals.com/samsung/

Basic knowledge of electronic components
Arduino Sensors
ESP 32