RAR archive for the IBM-branded ThinkPad X220 referencing Wistron and the Dasher-1 project name, about 2.01 MB. The name suggests the board was designed by Wistron as ODM, and the contents are most likely a schematic, though the archive itself does not state that. Extract it with WinRAR or 7-Zip and check what is inside. Use the material to trace power rails, follow signals and locate shorts, and confirm the project name and revision on the drawing match your motherboard before relying on it.
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 @alischematics. Enginerys does not host this file.
How to open a .rar file
Compressed archive — the usual wrapper for a schematic + boardview pair or a BIOS + EC set.