P4 connector powered MB?

galvitron · 12-12-2007, 11:07 PM

Hello,

I have the Commell LS-372 motherboard, which has the P4 4-pin power connector as its only power connector. I have this set up in the house for setup and testing and I am using an old 400W PC power supply, which does indeed have the P4 type connector.

Problem: The PSU expects a signal through the 20 pin ATX big connector (not used) to turn on. Normally in a home PC (from what I understand) a switch on your case is connected to your MB, which when hit, signals the PSU through the 20pin ATX to turn on, which in turn send all the juice back down the wires to power everything. My MB does not have this signal, so how can I get the PSU to turn on???

I have a simple switch connected to the PW SWITCH pin headers on the motherboard and the P4 connector from the PSU is attached to the board. When I hit the switch, no go...no signal sent to PSU to turn on...

DarquePervert · 12-13-2007, 09:44 AM

Quote: Originally Posted by galvitron

Hello,

I have the Commell LS-372 motherboard, which has the P4 4-pin power connector as its only power connector. I have this set up in the house for setup and testing and I am using an old 400W PC power supply, which does indeed have the P4 type connector.

Problem: The PSU expects a signal through the 20 pin ATX big connector (not used) to turn on. Normally in a home PC (from what I understand) a switch on your case is connected to your MB, which when hit, signals the PSU through the 20pin ATX to turn on, which in turn send all the juice back down the wires to power everything. My MB does not have this signal, so how can I get the PSU to turn on???

Actually, the signal to intiate bootup is sent to a 2-pin header on the motherboard, not through the 20-pin ATX connector.
Look it up in your motherboard manual.

Quote:

I have a simple switch connected to the PW SWITCH pin headers on the motherboard and the P4 connector from the PSU is attached to the board. When I hit the switch, no go...no signal sent to PSU to turn on...

If you're using an ATX PSU for testing, you need to fool the ATX PSU into thinking the PC is "on". short pins 13 & 14 on the 20-pin ATX power connector to fool the PSU into believing it's powered on. Unless teh ATX PSU thinks it's powered on, it's not going to send power to that 4-pin P4 connector.

There's a diagram of the ATX power connector in this FAQ: http://www.mp3car.com/vbulletin/advf...iew&advfaqid=4
Look down at the very bottom of the page.

galvitron · 12-13-2007, 11:37 AM

Quote: Originally Posted by DarquePervert

If you're using an ATX PSU for testing, you need to fool the ATX PSU into thinking the PC is "on". short pins 13 & 14 on the 20-pin ATX power connector to fool the PSU into believing it's powered on. Unless teh ATX PSU thinks it's powered on, it's not going to send power to that 4-pin P4 connector.

That is exactly the info I needed. Thanks a bunch for your help

Here is the WIP thread if interested:
http://www.mp3car.com/vbulletin/work...-dash-wip.html

turbocad6 · 12-13-2007, 11:55 AM

you will need to build a circiut that will close those pins when the pc is on, & opens it when the pc shuts down.
you can do that pretty easily, but you do need to do that to have the ps aware of the pc state. if you just jump it the ps will always be on.

the green wire in the 20 pin plug needs to go to ground when the pc is on. the best way to do this is to use a 5v relay that is tripped by the usb power output, & have that ground the green wire, works perfect every time & this is what needs to be done when using an atx ps with a laptop or any other non atx type pc.

galvitron · 12-13-2007, 12:04 PM

Thanks for the input Turbocad! I will only be using this normal style PC PSU for install and setup, so do you think I will need the circuit or can I just switch the PSU on and off with the switch on the back for now? Is there any danger in just jumping the pins and using the switch?

When it is in the vehicle it will use an M2-ATX. Does the M2 expect ground on that pin also to turn on? Maybe this is why I think my M2 doesn't work...

turbocad6 · 12-13-2007, 12:44 PM

yeah man, you have to do that with the m2-atx

turbocad6 · 12-13-2007, 12:46 PM

oh, & there is no danger in using it that way to set it up

galvitron · 12-13-2007, 12:50 PM

Cool, I think everything will be rosy now. Will post results tonight...

turbocad6 · 12-13-2007, 12:57 PM

good luck with it

galvitron · 12-13-2007, 10:50 PM

Okay. Works perfectly with the normal PC PSU. Awesome stuff and thanks again!

One more issue I have. I hooked up my M2-ATX and when I short the pins 13 and 14 the motherboard turns on for like 5 seconds, then shuts off...any ideas?

turbocad6 · 12-14-2007, 05:32 PM

that's a little tough to say... you hooked it up the same as the desktop ps? you would have to use a meter & find out what's going on... you mean even if it's manually jumped it still powers down after 5 seconds?

galvitron · 12-14-2007, 05:39 PM

I hooked it up basically the same as the desktop PS. 12 from wall adapter to M2, P4 from M2 to P4 on MB, MB pwer switch connected to appropriate pins on M2. Then I short the pins on the M2's 20pin ATX and the MB starts, then stops after 5 secs. If I "unshort" the pins within those 5 seconds, it immediately powers everything down...

confusing to me...

I did this with just the MB, CPU and RAM being powered (CPU = 35W) so I don't think it is overdrawing power.

adamopel · 12-18-2007, 11:55 AM

maybe it can help you.... it is from Hardware Book.

galvitron · 12-18-2007, 04:50 PM

I was pointed to this thread:

http://www.mp3car.com/vbulletin/powe...od-photos.html

It seems to describe my issue. I will try it and then post results.

turbocad6 · 12-18-2007, 05:41 PM

so a timing problem? you can test this before doing the smd cap by manually pressing the power button for the right lenght of time at the same time the psu is doing it... if your problem is the same then it means your turn on pulse isn't long enough... that's what the cap does is extends the button press several ms longer...

& adam, thanks for the diagram, I automaticly assumed he would have got that naturally in a google search at the first signs of any issue...