Main board schematic for the Xiaomi Redmi 3A, with a Chinese title, supplied as a 1.39 MB PDF. It contains the circuit drawings needed to trace power rails, check what hangs on a shorted line and follow signals from the processor and PMIC to connectors and peripherals. Open it in a PDF reader and search designators to cross-reference with the Redmi 3A component location map. Verify that the board revision printed on the PCB matches the drawing before relying on specific component values.
The button opens the matching file on RM Schematics, or a source page if it is not catalogued there yet. The original attachment is from @mobileschematicshub. Enginerys does not host this file.
How to open a .pdf file
The standard format for schematics, block diagrams, power-sequence charts and service manuals.