In article 319606a6-c15b-4094-9063-
, says...

The input is a bridge rectifier, ie the 4 diodes are connected in a ring.


Agreed. But, given the OP's stated lack of electronics
knowledge it might be helpful to explain that the bridge can
be visualised as being one diode on each side of a square with
the AC input to diagonally opposite corners. The other corners
are the positive and negative outputs.

On the PCB, the square has been squashed into a thin rectangle
with the AC input to the central connections to the pairs of
diodes like this (must be viewed using a fixed width font):


D1 D3
!-----!-----!-----!-----!
-ve ! AC ! +ve
!-----!-----!-----!-----!
D2 D4
--

Terry

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