Handsfree (headset) section of the Samsung SM-A20S schematic, a 2.07 MB PDF. It shows the headphone jack connections, detection line, audio left and right outputs and the headset microphone path with its filtering parts. Technicians use it when wired earphones are not detected, the phone stays in headset mode, or audio on the jack is missing on one side. Open it with any PDF reader and trace each line from the jack toward the audio codec, confirming the device is the SM-A20S before comparing.
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.