Also, when you mentioned the words 'diode bridge', I thought of these things. There are 3 of these little black cylinders with the silver collar. They are labelled D1, D2 and D3 on the board.
There is also a hockey puck-shaped thing labelled BR1. They are all very close to the power switch , the 4 biggest caps, and the '0V 15V 15V' landing. I tried to indicate D1 D2 and D3 with red lines.