RAR archive, 616 KB, for the ECS 661FX-M motherboard in letter revision A. Beyond model and revision, the file name carries no information about the included documents. Once extracted, a schematic can guide checks on the VRM, memory supply and chipset rails and help locate the BIOS chip and front-panel power signals. A revision 1.0 package for the 661FX-M is also present, so confirm which revision your board carries before following the nets.
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 @IT_SERVICE_WORLD. 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.
7-ZipWinRARThe Unarchiver (macOS)