Switching ON an ATX power supply (when it's not connected to mobo) ?

Discussion in 'Gigabyte' started by Huang, Apr 18, 2004.

  1. Huang

    Huang Guest

    Hi! does anyone here know how you can turn an ATX
    power supply ON when it is not connected to the mobo?
    I remember reading somewhere that we must touch (short)
    the blue and white wire together for a moment.....
    And to OFF the ATX supply, we must again short the blue
    and white wires for 3 to 5 seconds?
    Can anyone confirm?
    A perfectly functional motherboard or CPU can be damaged
    if the 3V, 5V and 12V lines are wildly off their mark and it is
    prudent to check the PSU out of circuit before connecting.

    Huang, Apr 18, 2004
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  2. Huang

    Ben Pope Guest

    Be very careful to get your orientation correct - you should be able to do
    it from the wire colours, but I prefer to check it by the keying (square
    pin) and don't forget that the direction you look at the connector (or the
    socket) affects this.


    Short pin 14 to one of the ground pins (I think I did it to 15, or 13). The
    PSU will be on whilst the wire is there, when you remove the wire, the PSU
    will turn off.

    Despite the power switch on the case (to the motherboard) being momentary,
    the "PSU on" signal is active low (active when grounded, otherwise it floats
    high I guess)

    Don't forget that some PSUs will not be able to correctly regulate their
    rails unless they are loaded, therefore I suggest you connect a suitable
    resistor (suitably high value to sufficiently limit the current to what the
    PSU is capable of, and suitably rated for the power it needs to dissipate)
    from the rail you wish to check, to ground and measure the voltage across
    the resistor.

    If any of that does not make sense, don't do it.

    Ben Pope, Apr 18, 2004
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  3. Huang

    Ben Pope Guest

    These comments relate to a digital multimeter. An analogue one might have a
    low enough resistance to source a suitable current. But nobody uses
    analogue voltmeters any more, do they? :p

    Ben Pope, Apr 18, 2004
  4. Huang

    Jim Schuster Guest

    I use one of these:

    Jim Schuster, Apr 18, 2004
  5. As others have mentioned, pin 14 to ground.
    Er, not really it ain't, it won't teach you anything. Switched mode power
    supply output voltages often appear "wildly off the mark" when there's no
    load applied to them, and so you might mistakenly believe the PSU is bust if
    you "dry test" it in this way.

    Besides, shorting wires to ground when you don't know exactly what you're
    doing could easily get you in more trouble than not doing so... ;)

    Good bit of cross-posting BTW...

    Richard Hopkins
    Cardiff, Wales, United Kingdom
    (replace .nospam with .com in reply address)

    The UK's leading technology reseller www.dabs.com
    Get the most out of your digital photos www.dabsxpose.com
    Richard Hopkins, Apr 18, 2004
  6. Huang

    Paul Guest

    If you like glowing LEDs, try one of these :)


    At least the circuit card would give you a base to connect more
    load resistors if you want.

    Soldering a fan to the +12V on the circuit board will also give
    you a supply of cooling air to blow over the resistors. I
    have some load resistors at home for testing ATX supplies and
    they get pretty hot - an 80mm fan keeps them from frying. You
    have to work out the ohms needed and power dissipation required
    for each load you construct.

    Paul, Apr 18, 2004
  7. Huang

    Inglo Guest

    Inglo, Apr 18, 2004
  8. The safest way to test the power supply that I've found is to buy an Antec
    power supply tester. You can then test the power supply without needing to
    connect to a motherboard. Maplins have them.
    Edward J Martin, Apr 18, 2004
  9. Huang

    Arnie Berger Guest

    You can try to plug in an old hard disk drive to one of the spare
    connectors. That might load the PSU enough for it to go into
    regulation. I think that they still regulate of the 5V rail.

    Arnie Berger, Apr 18, 2004
  10. Huang

    John Guest

    This one is easy!

    Simply short the green wire on the power supply connector (there's only 1 green)
    to any black wire, it will then power up without having to be connected to the


    John, Apr 18, 2004
  11. Huang

    w_tom Guest

    All of which is still unnecessary if one first and simply
    verifies the power supply even claims to have functions found
    in 30 year old power supplies. The safest way to test a power
    supply is to first verify it has standard and necessary
    functions. $20 and $40 power supplies typically do not which
    means inferior power supply still threatens computer - even if
    Antec power supply tester says it is OK.

    IOW the Antec power supply tester is necessary because power
    supply is missing essential and required functions.
    w_tom, Apr 18, 2004
  12. Huang

    Dumdedo Guest

    Car tail/stop light is very good as a load..
    Dumdedo, Apr 19, 2004
  13. What? A good analogue voltmeter should have high internal
    resistance, comparable to a digital voltmeter! If your
    0-20V DC voltmeter has sub-megaohm internal resistance,
    don't use it! Or, your measured voltage is not the
    potential difference without the voltmeter.

    My 2 cents.
    Stephen Wong @ Hong Kong
    Stephen SM WONG, Apr 19, 2004
  14. Stephen:
    Any analog (note the spelling; please!) voltmeter should work fine (if known
    good accuracy) for testing a low-impedance source like a power supply. If
    anything; it's probably better !!

    "yah hafta know your test equipment" ; as well as the circuit your are

    I'm an old fart who's had a voltmeter in my hands since 1959.
    Keith Christensen, Apr 21, 2004
  15. I've got one; and it works. There's one small problem; the loads aren't
    big enough to "really prove out" a PS.

    Maplins >> UK/EU>> 220~240V "mains" ; I'm a Yank with 110~120V . You can
    use the Antec "loadtester" here and it will probably "show good" even if the
    damned [110-220] switch is in the 220 position with 110 mains.
    Keith Christensen, Apr 21, 2004
  16. Huang

    Ben Pope Guest

    The spelling depends on your location.

    I'm from the UK, it's "analogue", but I would not be arrogant enough to tell
    you your spelling was wrong.

    Ben Pope, Apr 21, 2004
  17. Huang

    Bill D Guest

    But apparently not been round long enough to learn that many words are
    spelt differently in different parts of the world. Actually
    "analogue" is more correct. "analog" is the lazy US spelling. And
    ".. the circuit your are .." is incorrect.
    Bill D, Apr 21, 2004
  18. Huang

    XMan Guest

    It's only more correct if that's the correct way it's spelt (or spelled, if
    you prefer) in your part of the world.
    It's not lazy, it's phonetic.
    XMan, Apr 21, 2004
  19. Given the origin of the word from French and ancient Greek, "analogue"
    is more correct. But usage would accept either. It would depend on
    who is marking the spelling test - a UK teacher or a US teacher.
    here_and_there, Apr 21, 2004
  20. Huang

    Dodgy Guest

    Okay, okay, chill out guys or this is going to start into one of those
    arguments... (I'm English by the way).

    For those that want to have the argument anyway, he's some ammo.

    USA - Invented the internet
    UK - Tim Berners Lee invented the web
    UK - Invented the computer, mechanical and electronic versions

    And before anyone starts digging up history, yes the Americans where
    very helpful in the 1940's, although they did take a bit too long to
    come and help - It started in 1939 you know guys! And cheers for the
    mustang, nice plane, pity we had to show you how to make a good engine
    to make it useful. :p

    Okay, that's fanned the flames a bit... Hehehehe...

    /me runs away singing "You say potato... and some of your politicians
    say potatoe..." *snigger*

    Dodgy, Apr 21, 2004
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