Network section schematic for the Samsung SM-A21s, a smaller 1.93 MB PDF. It covers the cellular radio part of the board, typically the RF transceiver, power amplifiers, antenna switching and their supply rails. Technicians rely on it for no-service, weak-signal or no-baseband faults, checking RF supply voltages, tracing the antenna path and locating filters and test points. Any PDF reader opens the file. Verify that the handset is the SM-A21s, since RF circuitry varies between models and regional variants.
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 @phoneSchematics. 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.