PDF datasheet, 206 KB, for the SG3525A regulating PWM controller, revision 2F of the document according to the name. This IC is widely found in push-pull and half-bridge power supplies, UPS units and DC-DC inverters. The sheet gives the pinout, 5.1 V reference, oscillator setup with RT and CT, dead-time control, shutdown and soft-start behaviour. During a no-start fault, measuring the reference pin, oscillator waveform and output drive against these specifications quickly narrows down the problem.
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 @datasheet_technar_org. 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.