What exactly does the 4 pin 12v power connector do?

Howdy, I'm trying to troubleshoot a problem with a computer I'm building. I've been searching and searching and cannot find the answer to this.

My power supply has a 24pin and a 4pin connector, and the motherboard has equivalent sockets. The 24pin socket is on the side, and the 4pin 12v is up near the CPU.

It is an Antec True Trio 650 and Asus P5N-E sli, but this is a general question.

What exactly does the 4 pin connector power? All I find is that it adds additional power for stability, and is needed to boot. What I find says "boot", not "post", but I'm not sure if the terms are being used interchangably or not.

Anyway, does that provide processor only power? PCI bus power? More general overall power?

I'm having problems with using that connector, and am trying to find out exactly what it does.
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  1. Quote:
    It provides power to the PSU.

    How about listing your full system specs and the problem you are having.

    By any chance, was that a typo for CPU?

    I have a thread about the no post problem
    but here's where I am:

    I currently have my ATX chassis, the Asus p5n-e sli mb, an e6600 conroe c2d proc, and that is it.

    I have no dimms in currently (was testing for memory beep codes), no expansion cards, no external devices like keyboards. I do not have power plugged into any drives: just the 24pin connector on the mb and sometimes the 4pin 12v connector. And of course the CPU fan.

    What happens is, if I have both 24pin and 4pin power connectors to the system board, I can plug it in and get the standby LED, but when I hit the power switch, I'll either get absolutely nothing (no beeps and cpu fan won't spin) or the cpu fan will twitch briefly and that is it.

    However, every time I disconnect the 4pin 12v connector, the system will actually respond a little bit more--the cpu fan will spin for about 15 seconds then stop.

    Adding one dimm (either one) or two changes nothing, same with a video card.

    I have swapped psu and now mb. That leaves the cpu as suspect, but, I may have, in my frustration, caused a problem with the 2nd mb. I originally had only sufficient mb standoffs, but since the board was flexing some when I was plugging things into it, and I thought that might be part of the problem, so I added extra standoffs where none were needed. Now I realize that they might have been causing a short perhaps.. I've removed them and am now back to the 6 that match the mounting holes.

    So, I'm suspecting either cpu, or the mb again, or both? Not sure, and I've lost a lot of sleep over this :oops: Since it seems to tie in at least to some extent to that 4pin 12v connector, I figured I would try to find what it does.
  2. Thanks for the response.

    I think my first mb was defective. It would not provide power at all.

    I don't see any scorching or anything on the current mb, and I've checked it pretty thoroughly. There's no burning smells either. I've removed the extra standoffs.

    Any thoughts on whether the cpu may be good/bad still?

    /edit: Editing some in thread to remove miscellaneous info and rambling
  3. Quote:
    You won't know till you get a new board or take it into a shop.

    That makes sense.

    I'm just afraid of getting into a situation where a proc kills a mb which kills the next proc and so on. Perhaps I'm paranoid though.

    Thanks for the help!
  4. there's a lot of people on here who know more than me but my vote would be the mb. i have a bit of exp. on dead boards...when i first built my new system almost a month ago, the first board lasted a week, then it shorted out. the 2nd one died after a "successful" bios update, the 3rd and 4th were DOA. my 5th one is working great. everyone at fry's was saying that they've seen a lot of DOA boards lately. i doubt you got yours from there, but if they have a lot of bad boards, maybe a lot of other dealers do too.

    sorry for the long post..
  5. In case anyone was curious, here is an update. A late update, but an update none the less. :oops:

    I've had the computer build working for a couple weeks now. It was the motherboard. So it went roughly like this:

    1) First motherboard looked suspicious on arrival--box packaging wasn't flush, and there was a fingerprint on CMOS battery and some dust? or something on the backside. This mb was DOA and wouldn't post.

    2) I went to store and bought the second mb. Initially it didn't post (which could have been anything--ie, I could have perhaps not had a power cable pushed quite all the way in or some other component seated properly.) The frustration of the first DOA mb combined with the second one not working immediately pushed me into that Dangerous Frustration Mode, where you start taking 'imaginative' methods to solve the problem.

    3) In my case, Dangerous Frustration Mode led me to notice the motherboard flexed quite a bit when trying to plug stuff in. Aha, I'll just add some more standoffs to solve that flex!

    4) Silly me, I shorted mb #2 with this creative thinking.

    Anyway, after I got another motherboard, it worked better. Well, I got it to post. But then I had the fun and joy of not being able to install Windows XP. It kept locking up on the "Setup is starting Windows" portion of the Off-Cd install.
    -I had already disabled all unused ports in BIOS and was running default settings other than that.
    -I updated BIOS.
    -I tried running minimum config to install (one dimm, proc, mb, psu, scsi controller for my hdds, optical drive, video card)
    -I tried changing my HAL mode to non-ACPI and ACPI multiproc
    -Resetting BIOS defaults

    Anyway, to shorten that story, I found that my scsi card, which worked perfectly fine in my previous system, would not work in this one. It was acting like it had an IRQ conflict, but yet I had disabled pretty much everything in the BIOS--the only onboards I left enabled were PATA, USB, and LAN. The card wouldn't work in either PCI slot. But fortunately I had a spare older scsi card, and that one worked fine.

    So now the system's up and running fine, but I have to use the older scsi card.

    Thanks again for everyone's help, and if anyone wanted to know what happened, there it is. :)
  6. I figure this is as good of a place as any to post this. I've recently bought a bunch of new parts to upgrade my computer from an athlon 800 (Yeah it's a bit of a jump) I've never done this before but I wanted to try it out.

    Now I have a MSI k9n Neo Motherboard and amd x2 3800 cpu and a radeon 1650 pro video. Now I'm pretty sure I need a new power source but I want to make sure thats my only problem before I continue. My Power source now(being so old) doesn't have the atx 12v power cord. Is this why nothing happens when I turn on my computer?

    I opened the case and the cpu fan and video card fan both start up as well as all the lights come on but nothing else... my monitor says no signal avaiable and it doesn't sound like much is going on.

    Just curious if anyone could say something before I spend my money on a new power supply. thanks. Or if there is somewhere else I should be posting let me know.
  7. Quote:
    My Power source now(being so old) doesn't have the atx 12v power cord. Is this why nothing happens when I turn on my computer?


    If your current PSU can handle at least +12v@15A continuously you should not have any issue with it and get an adaptor for the CPU

    4-pin +12v molex adaptor @ directron (I am sure there are cheaper ones search a bit).

    Otherwise, if it is a case-bundled generic don't bother - at least get something like this HiPro 400w <$38 shipped @ newegg should work well for your setup.
  8. questin: i started troubleshooting my sysem that i buidl: i push power it blinks and no power, found that i can pull the 4 pin power plug it will come on but of course no picture.. tried other ps and same results. i was playing far cry when this happen. amd 9950 with 8 gb, gigabyte motherboards, gtx260 video..

    question: is it the cpu or the motherboard? thanks
  9. In response to your original question:

    The 4 Pin ATX12V connector supplies extra power to motherboards. It was originally developed for Pentium P4 systems but it quickly spread to motherboards designed for other cpu's.

    Later the 8 Pin EPS12V connector for dual processor motherboards in servers came into use. The 8 pin EPS12V connector was eventually adopted for use with dual core and quad core systems.
  10. my motherboard does have the 8 pin but 4 have a cover over them maybe i should connect all.. the amd 9950 quad cpu maybe needs it. i found out the motherboard is bad.. i have another one but still have only he 4 pins plugged in maybe i need to plug the rest in.. spme how thw 4 pin plug was shorted or something.. does the quad cpu need all 8 pins power???

    please advise..

  11. jumper,

    Yes, remove the plastic cover that covers 4pins of the 8 pin header on a motherboard and insert the 8 pin connector from the power supply. The 8-pin configuration was adopted for dual and quad core systems. Most motherboard manuals are poorly written and do not mention removing the plastic cover. A while back during a previous build I had to go to an ASUS forum to find out.
  12. thanks
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