Originally Posted by 
superquag
				 
			I've sent you up the garden path...
You need to operate it from the LENS, near the front. - A little lever that has a set-screw in it (to prevent inadverdant use) which 'exposes' a  T  or  A .
Basically, undo the screw to free the lever,  Cock the shutter, move lever so as to expose the  "T".  
Open shutter with the shutter release (as normal)  - will stay open......
To close the shutter, slide the lever across to its normal  ( shows "A" ) position.
The above taken from that link I posted.   Section 6 Page 14.    :-))
Many years ago I owned a Bronica S2A.. Fantastic beast, not so great for daylight flash-synch... 1/40 sec.  :eek:    Mirror and shutter blinds etc were so heavy that you could really feel it jump in your hands.