Auto power up of ATX PCs.

Pin 14 on the ATX power supply connector is the "PS-ON" signal. From the ATX spec:

PS-ON is an active low signal that turns on all of the main power rails including 3.3V, 5V, -5V, 12V, and -12V power rails. When this signal is held high by the PC board or left open circuited, outputs of the power rails should not deliver current and should be held at a zero potential with respect to ground. Power should be delivered to the rails only if the PS-ON signal is held at ground potential. This signal should be held at +5VDC by a pull-up resistor internal to the power supply.

So, you should be able to hack it together to have that pin permanently grounded, so that the PS is always on. I haven't tried this; I think it should work fine, but don't blame me if your motherboard burns! :-)

There's also more info on ATX at http://www.teleport.com/~atx/

Re:Do it in hardware (Score:5, Insightful)
by komet on Thursday May 27, @12:38PM EDT (#251)
(User Info) http://www.microsoft.com

We do this with all our servers (medium-size ISP in Europe) and it works without any problems at all.

Just take a bit of the isolation off the wire of Pin 14 (usually, bit NOT ALWAYS green). There's a GROUND signal on either side of this; take the isolation off that as well. Then solder together and wrap with insulating tape. Works like a charm. The only thing you shouldn't do is tell the mobo to power off; it gets a bit confused then.

This is where pin 14 is:
Looking down onto the contacts: (wires on rear)
v--(plastic tab)
===
+ + 0 # 0 + + + + +
+ + + + + + + + + +

# is pin 14. 0 is ground signal, should be a black wire.

Do it with hardware (Score:5, Informative)
by SEWilco on Thursday May 27, @01:15PM EDT (#440)
(User Info)

At hardware and auto parts stores you can get solderless connectors which tap a wire into an existing wire. You can use two of them to add a wire which connects the wires for pin 14 and a neighboring wire. They're usually blue plastic with a metal tab which you push into the two wires. Faster than soldering and can be removed for maintenance.

have just done this (Score:2, Informative)
by Anonymous Coward on Thursday May 27, @01:05PM EDT (#354)

I had a motherboard (DEC AlphaPC 164) that didn't produce the DC-OK (aka PC-ON)signal. This is pin 14 on the ATX motherboard connector. You can cut this wire (usually green colored) and the adjacent black (pin 15) wire above the connector and wire them together with a wire nut so that it is always on whenever the power cord is plugged in. Or connect these two wires to a new switch and replace the ATX style switch on your case with a standard AT-like switch (this is what I did). I bought the switch at radio Shack for under a dollar. Works great. The only thing the DC-OK wire does is tell the power supply to go from sleep state to full power state. It does this when the pin is grounded. The black wire #15 is one of those unneeded ground wires that can be redirected to this task. I was educated to this method by PC Power and Cooling (www.pcpowercool.com) which is probably the finest producer of power supplies out there. Good luck.

Re:Do it in hardware (Score:2, Informative)
by Knight (fireball@magic.nospam.hurrah.com) on Thursday May 27, @01:38PM EDT (#663)
(User Info) http://magic.hurrah.com/~fireball/jive.cgi

Actually, I have done this myself many times. IMHO, the best way to do it is to find the two-wired connector that connects to the mobo and controls the power. You simply short these two wires, and the PS stays on.

Faster than a speeding ticket!

Re:Do it in hardware
by Anonymous Coward on Thursday May 27, @02:39PM EDT (#918)

some mobos don't have the connector at all (such my DEC board mentioned above).

Re:Do it in hardware (Score:1)
by Knight (fireball@magic.nospam.hurrah.com) on Thursday May 27, @02:44PM EDT (#946)
(User Info) http://magic.hurrah.com/~fireball/jive.cgi

True, and in these cases, there is still some sort of a switch that the Motherboard uses to turn on the PS. As others have said, you just need to find out which wire to ground.

Faster than a speeding ticket!

Re:Do it in hardware (Score:2, Informative)
by mistered on Thursday May 27, @06:17PM EDT (#1552)
(User Info)

Just a little note: Not all ATX power supplies will work with this setup. At work we use ATX supplies for bench-testing some of our equipment (non-PC) and at least one ATX supply will not power up with the PS-ON connected to ground. The power supply will only switch on when the PS-ON signal goes from being open to being grounded. I don't think anyone will have a problem with most of the ATX supplies out there, but some of them won't work with this mod.

Mod to keep power on all of the time (Score:4, Insightful)
by el_steevo on Thursday May 27, @12:23PM EDT (#137)
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From the power supply wires coming from the power supply in the case to the MOBO, short the green wire to ground. This will give you power all of the time.

Re:Mod to keep power on all of the time (Score:4, Informative)
by aressa on Thursday May 27, @01:23PM EDT (#532)
(User Info)

Make sure you drop a 10kohm resistor in there, or you will reduce the life of the power supply. We ran into this same issue with some boxes that we wanted to boot right up when power was applied, soldering gun and a handfull of Radio Shack Resistors later we were golden...

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