Archive pairing PTB50 with the FIC XTB70 board, about 1.31 MB in RAR format, with no revision stated in the name. Both codes follow First International Computer naming, suggesting related or shared designs, though the exact relationship is not given. Extract the file with 7-Zip or WinRAR to reach the documentation, likely schematic pages. Use them to follow power rails, check signals and find test points, and confirm which board code and revision appear on the actual PCB before relying on any value.
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.