Use of blender's PSU
Unless you are comfortable with and competent to work with AC Mains power that is NOT isolated, you probably should not attempt this project.

The clue that this is dangerous is the blue and brown wires on the right-side of the board.  This board is powered directly from the AC Mains and there is NO isolation from the mains.

All that said: if you want to proceed, you need to do some work.

The very first thing to do is to trace the board out and create a schematic diagram showing all of the parts on the board and how they are connected together.  Modify your question by adding the schematic that you created.

Only then can anyone else provide meaningful advice.