Main > Main Forum

Powering on your cab without hitting the power button: the cap trick

Pages: << < (6/7) > >>

SirPeale:

I'd hardly call it "extra" work.  Connect (in some fashion) a capacitor to the power on pins on your motherboard.  I used a feature connector, but if you really wanted "extra" work, remove the pins altogether and solder it in.

Some motherboards really don't like having the power on wire on the power supply connected to ground, and won't do anything at all.  I've seen several.

Zebidee:


--- Quote from: RandyT on December 11, 2008, 04:20:30 am ---
But as it is presented in the context of an ATX supply, it seems to be overkill and that is what was confounding me.  I haven't seen a PC with an ATX supply where simply grounding the "power on" (green) line on the supply has created an issue. 

--- End quote ---

Interestingly, I once argued your point in a thread Randy, but I changed my mind once I saw how broadly useful the trick could be.

You're right that the ATX usefulness of the cap trick is limited.  The cap trick is very useful for PCs (eg with AT power supplies) that, for some reason, can't be set to auto power on when power is applied.  However, vaguely modern PCs runing WinXP on an ATX machine can do auto power-up anyway so it is irrelevant.  

Now, so that noone gets the wrong idea, I'd better tell you that you can't use the ATX pin 14 (the green PSON wire) as a momentary power-on switch.  This is purely an on/off.  Short this pin to GND to switch power supply ON, and while it is shorted the PC is on.  However, disconnect from GND and the PC will IMMEDIATELY switch OFF.  The cap trick will NOT WORK with pin 14.

A PC's Momentary on/off is actually controlled by the motherboard, which is why you need to use the cap trick on the power on/off switch on the mobo (look for the front panel header), not from ATX green pin 14.  I believe that this is the way that Peale has described the cap trick on his site.


Zebidee:


--- Quote from: Peale on December 11, 2008, 06:54:03 am ---I'd hardly call it "extra" work.  Connect (in some fashion) a capacitor to the power on pins on your motherboard.  I used a feature connector, but if you really wanted "extra" work, remove the pins altogether and solder it in.

--- End quote ---

You can "install" the cap just by shoving the pins into the back of the power switch connector on the motherboard.  Would take about 2 seconds, I reckon!

RandyT:


--- Quote from: Peale on December 11, 2008, 06:54:03 am ---I'd hardly call it "extra" work.  Connect (in some fashion) a capacitor to the power on pins on your motherboard.  I used a feature connector, but if you really wanted "extra" work, remove the pins altogether and solder it in.

Some motherboards really don't like having the power on wire on the power supply connected to ground, and won't do anything at all.  I've seen several.

--- End quote ---

Well, one method requires a cap and the other requires a sharp fingernail (in its crudest form :))  Maybe not a big deal if you happen to have a bunch of capacitors of the right value laying around, but most, I would guess, won't.  Measuring for polarity, etc, also takes time, effort and expertise with a meter.  It's quite different than jumpering the green wire to the black wire next to it (and jumpers don't explode when you reverse the polarity.)

Would you happen to know which boards don't work with the ATX power on jumper?  It seems odd to me that a piece of electronics could refuse to operate when given power, but nonetheless, I'd be interested in steering clear of them.  BTW, some power supplies need a hefty load on the 5v supply for them to turn on.  Just having a motherboard attached might not be enough.

RandyT


*edit*  It seems like an item like this would be a good one to have on your store.  Just plug in the pre-attached connector and problem solved ;)


RandyT:


--- Quote from: Zebidee on December 11, 2008, 06:57:46 am ---A PC's Momentary on/off is actually controlled by the motherboard, which is why you need to use the cap trick on the power on/off switch on the mobo (look for the front panel header), not from ATX green pin 14.  I believe that this is the way that Peale has described the cap trick on his site.

--- End quote ---

Actually, you kind of have this a little twisted.  The "Momentary" is simply the nature of the switch.  When you press it, it completes a very low power circuit which, you guessed it, pulls the "power on" line low (same as connecting it to ground) while waiting, as it always does with power applied, for the ATX supply to raise the "power good" line to 5v.  At that time, it starts the system.  The mobo doesn't care if you release the switch because it is now holding the "power on" line low with it's own circuitry.  Your job is done ;)

RandyT

Pages: << < (6/7) > >>

Go to full version