The 51.7 KB PDF named 300HF sits in the schematic index but carries no device, maker or board number. The code reads as a component series name, and the small size suggests a brief reference sheet rather than a full circuit diagram. Open it in a PDF viewer to see exactly what it covers. It can help confirm terminal arrangement before soldering a replacement. Check the full marking on the part, including any suffix digits, against the document.
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 @cyberlanelectonik. 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.
Any PDF readerSumatraPDFFirefox / ChromeFlexBV (links PDF to boardview)