Schematic file named kvxa21m83, a 9.44 MB PDF with no brand stated. The code resembles a CRT television model number, but check the cover sheet to confirm the maker, model and chassis. Such schematics are used to trace the power supply, deflection and high-voltage sections, follow video and audio signals, and locate component values when a set shows no power, no raster or distorted pictures. Compare the chassis marking inside the set with the drawings before taking measurements or ordering replacement parts.
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 @datasheets1. 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.