Help in debugging Avid Digidesign XMON and PRE SMPS PSU

[saint gillis]

Hi,
I've retro-engineered this Skynet SMPS used in Digidesign XMON and PRE units.
Of course there might be a lot of mistakes, but here's the schematic :


At the bottom-left corner of the schematic there is a component (IC4) that is difficult to identify, it is labeled D173 :


The NPN transistor D1733 seems odd at this position, and measuring the junctions seem to indicate that it is a PNP transistor.. I'm a bit lost here

 

[Khron]

Well, the designator is "IC", so it's most likely NOT going to be a discrete transistor (designated "Q").

Going by where it's in the schematic though, odds are better it's a TL431 of some description.

Edit: Indeed, the pinout matches the datasheet.
https://www.ti.com/lit/ds/symlink/tl431.pdf

 

[saint gillis]

Thank you, that makes sense, I've edited the schematic