Desktop Power Supply Question

Discussion in 'Computer Support' started by LoneStar, Dec 21, 2006.

  1. LoneStar

    LoneStar Guest

    Simply put, when a desktop computer power supply is connected to a wall
    power outlet is there ANY voltage output from the power supply to the
    motherboard? Note that this is BEFORE the power switch is activated.
    Please help!

    EW
     
    LoneStar, Dec 21, 2006
    #1
    1. Advertising

  2. LoneStar

    doS Guest

    yes

    "LoneStar" <> wrote in message
    news:4589d6da$0$97264$...
    > Simply put, when a desktop computer power supply is connected to a wall
    > power outlet is there ANY voltage output from the power supply to the
    > motherboard? Note that this is BEFORE the power switch is activated.
    > Please help!
    >
    > EW
    >
    >
     
    doS, Dec 21, 2006
    #2
    1. Advertising

  3. LoneStar

    PeeCee Guest

    "LoneStar" <> wrote in message
    news:4589d6da$0$97264$...
    > Simply put, when a desktop computer power supply is connected to a wall
    > power outlet is there ANY voltage output from the power supply to the
    > motherboard? Note that this is BEFORE the power switch is activated.
    > Please help!
    >
    > EW
    >
    >


    EW

    Older AT and PC power supplies are 100% on or off as the switch on the front
    of the PC actually switches the mains AC on and off.

    Modern ATX power supplies however provide 5 Volts at up to 2 Amps to the
    motherboard whenever there is mains AC connected to the IEC socket at the
    back. This Voltage is used to power various convenience items on your
    motherboard and the 'Power On' circuitry.

    When you press the 'On' switch of your Desktop PC the 'Power On' circuitry
    detects this and instructs the main power supply to wake up and provide the
    rest of the voltages necessary for the PC to start up and function.

    The other convenience items are for example WOL (Wake up on LAN) where LAN
    (Network) activity or Wake up on Ring (Modem) will have the same effect as
    pressing the power button to turn your PC on.
    Some motherboards will also provide power to USB ports while the main PC is
    off, this can be usefull for charging USB devices.

    Cheers
    Paul.
     
    PeeCee, Dec 21, 2006
    #3
  4. LoneStar

    LoneStar Guest

    "PeeCee" <> wrote in message news:emcubf$k1k$...
    >
    >>

    > Older AT and PC power supplies are 100% on or off as the switch on the
    > front of the PC actually switches the mains AC on and off.
    >


    Thanks Paul. You've answered everything. FYI, I have an eMachines that's
    only 3 years old, apparently good power supply according to a good tech, but
    the unit won't turn on. No way. The power switch is good, as is the wiring
    to the MB. Guess it must be the motherboard. I checked the output of the
    PS with the unit plugged in and got nothing (.37 and .11 VDC on a couple of
    pins). Oh well, it will make good target practice fodder after I take out
    the PS, RAM, HD, and CD-RW.

    Thanks again.

    EW



    --
    Posted via a free Usenet account from http://www.teranews.com
     
    LoneStar, Dec 21, 2006
    #4
  5. LoneStar

    Shep© Guest

    On Wed, 20 Dec 2006 18:42:43 -0600 Too Much Ying and you will Pay With
    Yang then "LoneStar" <> sent this :

    >Simply put, when a desktop computer power supply is connected to a wall
    >power outlet is there ANY voltage output from the power supply to the
    >motherboard? Note that this is BEFORE the power switch is activated.
    >Please help!
    >
    >EW
    >


    Depends on what country you live in?



    --
    Free Windows/PC help,
    http://www.geocities.com/sheppola/trouble.html
    http://www.soundclick.com/bands/pagemusic.cfm?bandID=88558
     
    Shep©, Dec 22, 2006
    #5
  6. LoneStar

    Plato Guest

    LoneStar wrote:
    >
    > Simply put, when a desktop computer power supply is connected to a wall
    > power outlet is there ANY voltage output from the power supply to the
    > motherboard? Note that this is BEFORE the power switch is activated.


    Yes. Modern PCs are always ON.

    --
    http://www.bootdisk.com/
     
    Plato, Dec 23, 2006
    #6
  7. LoneStar

    PeeCee Guest

    "LoneStar" <> wrote in message
    news:458aff6a$0$15417$...
    >
    > "PeeCee" <> wrote in message news:emcubf$k1k$...
    >>
    >>>

    >> Older AT and PC power supplies are 100% on or off as the switch on the
    >> front of the PC actually switches the mains AC on and off.
    >>

    >
    > Thanks Paul. You've answered everything. FYI, I have an eMachines that's
    > only 3 years old, apparently good power supply according to a good tech,
    > but the unit won't turn on. No way. The power switch is good, as is the
    > wiring to the MB. Guess it must be the motherboard. I checked the output
    > of the PS with the unit plugged in and got nothing (.37 and .11 VDC on a
    > couple of pins). Oh well, it will make good target practice fodder after
    > I take out the PS, RAM, HD, and CD-RW.
    >
    > Thanks again.
    >
    > EW
    >
    >
    > --
    > Posted via a free Usenet account from http://www.teranews.com
    >


    EW

    <quote>
    I checked the output of the PS with the unit plugged in and got nothing
    (.37 and .11 VDC on a couple of pins)
    </quote>

    Whoa, hold it right there.

    At least one of the supply wires to the motherboard should have +5V on it
    when plugged into the motherboard and AC connected to the power supply. Have
    a look at the sticker on the side of the power supply, the one I picked up
    at random said +5V SB = Purple (SB = Standby)
    Even when the PC is off the 5V SB ciruitry is supplying power to the
    motherboard power switching circuitry.
    This is the voltage that allows the power switching circuitry on the
    motherboard to operate.
    It does this by powering a a transistor that is switched by the front panel
    microswitch to pull the (usually) Green wire to ground.
    So, no 5V, there is no way the power supply can be told to switch on even if
    the motherboard is Aok and the switch on the front of the case is in perfect
    order.

    Despite your good tech's advice that you have a 'good' power supply, most of
    the power supply's I replace these days just stop producing 5V SB. (that's
    excluding the ones with blown capacitor disease)
    I would suggest you try a substitute power supply if one is available.

    Best (& seasons greetings)
    Paul.
     
    PeeCee, Dec 26, 2006
    #7
    1. Advertising

Want to reply to this thread or ask your own question?

It takes just 2 minutes to sign up (and it's free!). Just click the sign up button to choose a username and then you can ask your own questions on the forum.
Similar Threads
  1. Silverstrand

    HEC Ace Power 580UB 580Watt power supply

    Silverstrand, Jul 23, 2005, in forum: Front Page News
    Replies:
    0
    Views:
    845
    Silverstrand
    Jul 23, 2005
  2. Silverstrand

    AOpen Prima Power AO700-12ALN 700W Power Supply Review

    Silverstrand, Aug 27, 2005, in forum: Front Page News
    Replies:
    5
    Views:
    1,453
    unholy
    Aug 29, 2005
  3. Silverstrand
    Replies:
    0
    Views:
    1,972
    Silverstrand
    Feb 21, 2006
  4. Willem van der Berg
    Replies:
    4
    Views:
    1,351
    Use.Netuser.de
    Oct 3, 2004
  5. nick
    Replies:
    0
    Views:
    1,359
Loading...

Share This Page