Studiomaster M1000 schematic, supplied as a 576 KB PDF. Studiomaster builds professional audio gear such as mixers and amplifiers, and a diagram like this is used to follow the signal chain, find the power supply section, read part values and check the voltages expected at key points while repairing noise, hum or dead channels. It opens in any PDF reader. The name gives no revision, so compare the board markings inside the unit with the sheets before replacing components based on the drawing.
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 @pdf_servicemanual. 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.