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

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.

TIA

 

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.

http://www.hardwarebook.net/connector/power/atxpower.html

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

 

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?

Ben

 

I use one of these:

http://www.cyberguys.com/templates/searchdetail.asp?T1=113+0282

 

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

 

If you like glowing LEDs, try one of these

http://www.dansdata.com/quickshot018.htm

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

 

You use that to get the second power supply for your GeForce 6800 Ultra
running I guess.

 

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.

 

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

 

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
board.

HTH

John

 

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.

 

Car tail/stop light is very good as a load..

 

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:
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
testing.

I'm an old fart who's had a voltmeter in my hands since 1959.

 

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.

 

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

 

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.

 

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.

 

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.

 

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.

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

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

D0d6y.