Deducing polarity by looking at a circuit board.

Discussion in 'General Electronics Chat' started by FDBennett, Jan 11, 2017.

  1. FDBennett

    Thread Starter New Member

    Jan 11, 2017
    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.
  2. MaxHeadRoom


    Jul 18, 2013
    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.
    Last edited: Jan 11, 2017
    #12 likes this.
  3. FDBennett

    Thread Starter New Member

    Jan 11, 2017
    Thanks, Max. Yes, a barrel jack.
  4. Marley


    Apr 4, 2016
    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!
    #12 likes this.
  5. RichardO

    Well-Known Member

    May 4, 2013
    Check the wires of the fan that plugs into the board. Hopefully they are black and red. If so, the red is likely positive.
    ErnieM likes this.
  6. hp1729

    Well-Known Member

    Nov 23, 2015
    Design 1028 fan switch.PNG

    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)