Schematic for the IBM ThinkPad T40 in PDF format, approximately 1.08 MB. Only the model name is given; there is no motherboard number or revision in the name, so check the PCB markings before treating this as the exact match for your board. Such diagrams are used to follow power rails through regulators, understand the power-on sequence, check signal connections between chips and pinpoint shorted components. Open it in any PDF viewer and use the search function to jump to specific net names or 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 @alischematics. 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.