Refer to astron linier PSU schematic:-
http://www.repeater-builder.com/astron/pdf/astron-rs50a-rs50m-rm50a-rm50m-1996-03.pdf
I aquired this broken 723 based PSU with blown components:-
CR1+2 35Amp diodes, 723 reg, q2, 3771 driver and diode CR5. I can easily repair, but cannot understand purpose...