By looking at this circuit board, anyone tell me which of the contacts is positive (+) and which is the ground (-)? It is a standard two pole jack. I do not have the transformer and the poles are not indicated on the device housing. Thank you.

 

If this is a barrel jack? Although the centre pin connection does not look in the normal place, but if this is DC input, the ground plane is usually the common (-ve). A & C. with B=+ve.
Max.

 

Thanks, Max. Yes, a barrel jack.

 

It is actually impossible to say because there are no polarised components on the board. However, it is common practice to connect the ground plane to 0V so I would guess that the centre pin of the connector is positive. Also it is usual to have the centre pin of a co-axial power connector as positive. Not always though. I have seen equipment with the centre pin negative.

So assuming the ground plane is 0V and everything else is positive, then you can see the polarity of each of the three output connectors.

Careful though - because you can't be sure!

 

Check the wires of the fan that plugs into the board. Hopefully they are black and red. If so, the red is likely positive.

 

Thanks, Max. Yes, a barrel jack.

3 Position slide switch? Off, high and Low?
Assumed Pin 1 of the FAN2 connector is toward the side of the board.
FAN1 and DC are not used.
Fan connector, pin 1 is power, pin 2 is ground. (best guess)