Reversing polarity on power supply

Discussion in 'General Electronics Chat' started by jhampa, Sep 14, 2012.

  1. jhampa

    Thread Starter New Member

    Sep 14, 2012
    I purchased a new power supply for an old computer. The power harness has 20 outlets and one wire is missing. On the PDF page two I am missing the white -5 volt wire on line 8. There are several +5 lines, is there a diode or something that I can attach to the +5 line to reverse the polarity to get a -5 line for that one output? In replying please be specific with the name of the item so when I go to Radio Shack or such I get the right thing. thanks if you reply
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
    No the psu is designed to give out specific voltages, you cant modify without a circuit diagram.
    The -5V is for the old floppy drive, your computer should work without this -5V.

    Do you mean the white wire on pin18 on page 3?
    Last edited: Sep 14, 2012
  3. BSomer


    Dec 28, 2011
    Since the power supply spec sheet does mention there being a -5VDC, it may actually ba available on the PCB just not brought out to the connector P1. As Dodgydave mentioned this was used in older computers with a floppy disk drive. If your computer does not have a floppy I wouldn't worry about the -5V supply.

    If you do need the -5V open up the power supply and see where all the wires go to. There may be some silk screen marking the different points on the PCB where the wires attach. If you see a spot that is not populated with the marking of -5V solder a wire there and take it to your P1 connector.
  4. paulktreg

    Distinguished Member

    Jun 2, 2008
    The -5V rail was dropped from the ATX power supply specification several years ago. I thought it was used on old ISA cards?