Apple iPhone 3GS schematic in PDF form, roughly 8.92 MB. Board-level diagrams like this let a technician follow power rails from the PMU, trace signal lines between the processor, baseband and peripherals, and find which components sit on a faulty circuit when diagnosing no power, charging or boot problems. Any PDF reader opens it, and text search for net names speeds up tracing. Check that the diagram matches the logic board variant you are working on, since sheet labels and part references can differ between revisions.
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 @schematicmobile. 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.