Schematic PDF of about 1.5 MB labelled only UBA 800, without a maker name or revision. The sheets can be used to follow the circuit stage by stage, check component values and locate likely failure points such as output transistors, supply rectifiers or protection circuits. Any standard PDF viewer will open it. Because the name carries so little identifying information, compare the model plate and the board markings of the device on the bench with the drawing before relying on any part value or wiring detail.
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.