Sir CanYouHelp . . . . .
Gravitated afterthoughts . . . .
With a limited view of ALL of the component side of the PCB, I believe that they are just using an " economy" technique on the power supply design for this board.
With more credence given to the RED and BLACK wires and connectors as being the switched output contacts of the power relay.
Specifically . . . . . I think that at the bottom left quadrant of the board that I see just the slightest minute glimpse of the edge of a BLUE cased varistor that is being across the AC line input to clip and suppress any sporadic high line voltage spikes.
That is being, to further protect the HOT side of the AC line, which is then being connected to the right terminal of the large YELLOW poly cap . . aka . .426124C with its AC input on its right side and AC output out its left side which then passes up and into and out of a 22 ohm 2W metal film surge / trimming resistor.
That hot AC then goes into a + - pair of the set of 4 full wave diodes, that uses the reduced AC voltage, created by the resistor PLUS the AC capacitance reactance of the poly cap, to feed the units low voltage supply.
Reading the MAX voltage rating of the MAIN capacitor should suggest the somewhat reduced voltage of the highest supply that feeds the power relay.
As well, the reduced 2 lower voltage ratings of the 2 other E caps, should estimate the voltages associated with the sub supplies.
You can see that top center TO-92 cased device has been assigned a Q 1. . . . .transistor . . .symbol identifier.
As well, the far right DIP packaged IC, has been assigned U3, with its companion to the left being U2.
Therefore, a like possibility, is for the suspicioned TO-92 just to its left, to be a U1 assigned 78L05 regulator IC.
That leaves relay driver transistor to be Q2.
At the top left corner I see a 3 conductor ribbed . . . . .WHITE- - - -WHITE RED BAR - - - - WHITE RED X . . .. that could relate to an adjustable pot connection, thermostat. or its outputting to LED's for run /state conditions ? ? ? as is to be confirmed.
Any further assistance on my part would be dependent upon a, squared within the frame , straight on, full frame, well lit, in focus, photo of the component side of the board with ALL of its components.
ALSO, a like photo of the OTHER foil pattern side of the board, so that I can " read " it.
BTW is this being an intermittent use type of ventilating fan, as might be used in the ceiling of a bathroom ?
73's de Edd
.....