PDF schematic labelled UL20A, a 1.32 MB circuit diagram for the notebook mainboard carrying that model designation; the name gives no board number, revision or brand. A schematic like this lets a technician follow power rails from the DC jack through the charger and voltage regulators, check enable and power-good signals and identify components near a suspected short. Any PDF viewer opens it with text search for net names. Compare the board number and revision silkscreened on the PCB before trusting values or part references.
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 @schematicslaptop. 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.