Using a hotwired power supply

[ShadowTek]

I know that you can connect the green wire and a black wire of a power
supply to turn it on while it's disconnected from the motherboard, but
can you leave those two wires spliced together *while* the power supply
*is* connected to the motherboard, or would that harm something?

Lets say I used a jumper pin to connect the two circuits from the *back*
side of the main connecter where the wires go in, and then plugged the
connector into the motherboard. Would that be bad?

 

[Sjouke Burry]

I know that you can connect the green wire and a black wire of a power
supply to turn it on while it's disconnected from the motherboard, but
can you leave those two wires spliced together *while* the power supply
*is* connected to the motherboard, or would that harm something?

Lets say I used a jumper pin to connect the two circuits from the *back*
side of the main connecter where the wires go in, and then plugged the
connector into the motherboard. Would that be bad?

Not if you want to do the ultimate survival test to your board....
But it is very nearly a suicide test mode.

 

[larrymoencurly]

I know that you can connect the green wire and a black wire of a power supply
to turn it on while it's disconnected from the motherboard, but can you leave
those two wires spliced together *while* the power supply *is* connected to
the motherboard, or would that harm something? Lets say I used a jumper pin
to connect the two circuits from the *back* side of the main connecter where > the wires go in, and then plugged the connector into the motherboard.Would
that be bad?

You can do that without causing harm because the signal is "open collector", so it doesn't matter if one output wants to keep the green wire at +5V and another output wants it at 0V -- the green wire will go to 0V if any output wants it at 0V.

Usually when a motherboard won't turn on the PSU when you hit the front panel button, the motherboard is in sad shape, but a month ago somebody mentioned that his motherboard would turn on and run normally when he shorted thegreen and ack PSU wires together.

A very few PSUs won't turn on if the green and black wires are connected before the AC power is activated. I've had some Deltas like that.

Some motherboards can be configured to automatically turn on after a blackout. Maybe you should see if yours can be set that way so you won't need tojumper the PSU wires.

 

[Paul]

You can do that without causing harm because the signal is "open collector" ...

That's the secret. As long as the motherboard driver end, is open collector
type, and only "pulls to ground", then there's no damage if you use
the shorting stub (green to black).

One reason for not liking the shorting stub idea, is you lose your
CPU thermal protection that way. If the heatsink falls off the CPU,
THERMTRIP won't be able to turn off the power, if your
shorting stub is being used. So you lose certain of the
protection features, the computer has in it.

Paul

 

[VanguardLH]

I know that you can connect the green wire and a black wire of a power
supply to turn it on while it's disconnected from the motherboard, but
can you leave those two wires spliced together *while* the power supply
*is* connected to the motherboard, or would that harm something?

Lets say I used a jumper pin to connect the two circuits from the *back*
side of the main connecter where the wires go in, and then plugged the
connector into the motherboard. Would that be bad?

What's your real objective? What are you trying to accomplish with the
PSU inside your case and connected to the mobo and devices with the
PSU-ON signal always grounded? Is it that you don't want anyone to
power off your computer using the front panel Power switch despite that
they could still yank out the plug on the backside of the case (out of
the PSU A/C connector)?

 

[Paul]

What's your real objective? What are you trying to accomplish with the
PSU inside your case and connected to the mobo and devices with the
PSU-ON signal always grounded? Is it that you don't want anyone to
power off your computer using the front panel Power switch despite that
they could still yank out the plug on the backside of the case (out of
the PSU A/C connector)?

People hotwire, when the regular motherboard PS_ON# driver
stops working. Your choices at that point are, replace motherboard
or hotwire. At one time, the PS_ON# driver was a separate chip, and
you could replace the chip (14 or 16 pin DIP). Now, the driver
could be a pin on the Southbridge that drives direct. And if it
blows, that's not home repair material.

If you want to (logically) keep a computer powered, you can
set the BIOS power setting, to turn on the computer after
a power failure. And that's the equivalent of keeping PS_ON#
asserted, but without compromising any other features.

http://www.instructables.com/image/FF88R0EG4D5WXC6/Restore-on-ACPower-Loss.jpg

Paul

 

[ShadowTek]

What's your real objective? What are you trying to accomplish with the
PSU inside your case and connected to the mobo and devices with the
PSU-ON signal always grounded? Is it that you don't want anyone to
power off your computer using the front panel Power switch despite that
they could still yank out the plug on the backside of the case (out of
the PSU A/C connector)?

I ended up with some damn custom HP OEM board that uses a proprietary
front panel connector. There are no markings on the board that say what
pins are for what, and there is NO documentatin for the board that is
provided my HP.

So that got me wonding what the simplest method would be to activate one
of these boards if I ever run into another in the future.