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6 pin PCIe connectors

K

keldog7

Senior member
Hi all,
This post didn't seem to fit well into the other forum categories, so...

My problem stems from a recent 7900GTX purchase, and the fact that it doesn't work right. After calling the manufacturer (who appears to be listening to my concerns - so far...), I have been told that the problem is my PSU...a Seasonic S12-500, which is rated for 16A and 17A, respectively, on each of its 12V rails (there are 2). Personally, I think the PSU suggestion is horse-$417. Without getting into a flame war (as has happened on at least 1/2 dozen forums), the question appears to boil down to this:

I'm using the 6 pin PCIe connect from the PSU to power the card. This connector is not necessarily supplied by only ONE of the 12V rails - otherwise the standard connecter would be a 4 pin molex. At Intel ATX 2.0 specification for PSUs apparently says that (for safety reasons) no 12V rail will have a current rated to exceed 20A. The nVidia spec for the 7900GTX apparently calls for 22A on the 12V line - without mentioning whether or not it is the SUM of the rails, or only one of them. Logically, I bet it has to be on ONE rail - but rumor has it that most PSU manufacturers don't REALLY limit the current on each rail anyway. Either way, it would appear that nVidia's power requirement EXCEED the maximum spec of any ATX 2.0-certified PSU... Again, this makes a good argument for creating the 6 pin PCIe connector - as it would not fall under the same rule as the 4 pin connectors... Thus, manufacturers could allow the 6 pin to run at higher (?total 16+17=33A?) current rating...but that is obviously speculation. The Seasonic brochure says that the 6 pin connector can deliver up to 150W...at 12V, that means 12.5A current max...which is worse than one of the 12V (ie 4 pin molex) lines!...and far short of the required 22A needed by the 7900GTX.

So..... Has anyone tested, or can anyone confirm exactly how much current can be delivered by the 6 pin connector - either on the Seasonic, or ANY other PSU?

Cheers,
Adrian
 
Your Seasonic should have no problem. I don't have the exact numbers for current drawing. But Seasonics are rated high on continuious voltage and strong rails. Can you tell us what is wrong with the 7900GTX instead, before jumping into any conclusions.
 
Originally posted by: Navid
What exactly is the problem?
Have you read this?
http://enthusiast.hardocp.com/article.html?art=MTA2OSwxLCxoZW50aHVzaWFzdA==
Click to expand...


The above has been posted on several forums, so gamers are coming to grips with it.


To address your question about current and 6 pin plugs, as well as 4 pin, 8 pin and 20/24 pin,
look about 15% down this page http://www.action-electronics.com/molex.htm 9 AMPS Max capacity per pin. When a 8 pin is combined to double up two of the four rails, the above should be given some serious thought.

Much, but at times confusing, information can be found at http://www.molex.com


...Galvanized
 
Yes, I intentionally did NOT post the problem I was having with the 7900GTX, because I didn't (AND DON'T) want this thread to degrade into yet another "that PSU should be fine" or "that PSU can't handle it" scenario. The manufacturer has instructed me to first re-examine the PSU - which I will be doing in about 45 minutes...I still think their suggestion is garbage, but having worked 2nd level tech support, I can appreciate that they want to start at the BEGINNING of the troubleshooting process. Their primary assertion is that the PSU can't supply enough current, and that 22A is the minimum needed... Since I'm using that 6 pin connector, I just want some objective opinions on how much current that line can actually draw (in my case, with a single video card).

...but in brief, the HardOCP site describes a VERY similar situation to what I'm experiencing...lots of artifacts, but without even pushing the card...it starts to artifact in Windows even before I complete the login. After 30-40 seconds (the artifacts persist and add up over time), the screen is unreadable...and unusable. Card at stock speeds (not an overclocked version), occurs with "plain-Jane VGA" and 84.21 drivers.

-Adrian
 
The 7900GTX is right on par for power requirements with the 7800GTX. As you can see from the power output of the cards from the post in this thread from Hyphe the 7800GTX draws 80.7 watts at full load.

While this is not an insignificant amount of power, 80.7w/12v=6.725A needed. Either of your two rails can handle this, as well as the molex connector.

Don't forget that the PCI-E slot is rated at 75w by itself.

Now, that isn't to say that your power supply is not at fault. Simply load up your computer with 3dmark or something and check the 12v line at the PCI-E connector. I seriously doubt a quality PSU like your Seasonic will even drop more than ten-twenty millivolts, but it would be the proper place to start.

p.s. If your video card required 22A then it would produce 264w of heat on its own - more than double even a top end P4 and would need one HECK of a heat sink. The "ratings" that GPU manufacturers require are complete horse crap, but they just want something to blame when Johnny plugs his 7900GTX into his 250w craptastic PSU.
 
Agreed. I received an e-mail from Seasonic tech support tonight, and they have advised me that the 6 pin PCIe connector should be MORE than enough to supply a *single* 7900GTX. I have asked him a more pointed question though: can the 6pin PCIe connector supply 22A on the 12V if it had to? No response yet.

I agree fully that the vid card maker's 22A requirement is utter horsep00p... But to play their RMA game, I just need to prove that my PSU meets their minimum...which I'm sure the Seasonic rep can prove, given the likely implementation of 12V on the 6 pin (i.e. its essentially a common rail, representing the sum of 12V1 and 12V2)...this is speculation on my part, because I can't seem to find any info on where that 6pin draws its power from... Anyone who is "in the know", please jump in and educate me!

Just the same, I used the supplied "2x4pin molex to 6 pin" adapter to connect separate 12V rails to the card...not a whit of difference. Artifact city, after waiting 15 seconds at the login screen. /SARCASM ON "I had no idea that the Windows 2000 login screen could be so brutally hard on the latest video cards!" /SARCASM OFF
-A
 
I'm going to help you out as much as I can because I feel your pain absolutely.

Okay here goes:

1) You have either a Evga or BFG card
2) The 7900 line has a lot of problems
3) The PSU suggestion is probably not the right cure

Out of all the headaches I've had with my friend's PC (Me of course, being uber nerd have to help set it up, they just play), they got artifacts.

First i thought it was heat... but lol and behold, CPU temperatures were low.

Then the Power Supply suggestion came about... not enough power.

But nope, fancy-smancy Antec TruePower PSU each at 500+

So what's the culprit? It's the damn video cards.

If it's a BFG or EVGA, the memory chips have voltage problems and are undervolted or getting overheated. No amount of ramsinks will help you, it's just pure crap.

Strictly my opinion (I really mean strictly an opinion), drop the 7900 line of cards and get an equivalent ATI card OR 7800 Series card to hold you over.

Replaced 2 video cards, one with a 7800GT and the other with a ATI 1900XT. WORKING FLAWLESSY ever since I dropped the 7900GT and the 7900GTX off their rigs.
 
FYI, I got another message back from Seasonic. First, the question I asked:

"Thank you for the prompt reply...may I ask one follow-up question?
You have said that I cannot identify the max draw from the 6pin connector because the 12V
is not dedicated to it. This makes perfect sense, of course... In your opinion, can the 6 pin
connector of the S12-500 (under typical circumstances) deliver 22A of current at 12V?"

The tech's response is a bit cryptic, but Seasonic users can at least draw some conclusions about the 6pin connector from their PSU:
"Hi Sir

I may say this way, the 6p connector is just one oulet of the 12V line
The total delivery at 12v of S12-500 is still 17+16=33A. Pretty enough for 22A request.
Thanks

Best Regards,
Support Team
Sea Sonic Electronics Co., Ltd.
Tel: +886-2-2659-0338
Fax:+886-2-2659-0530
http://www.seasonic.com
E-mail: support@seasonic.com.tw
Green Innovation Powers Your Life
Visit us during Computex Taipei 2006 at Hall 1 booth # 1211 & 1213 "

So that's it... Back to the manufacturer - hoping for RMA soon.
-A
 
I hope it works out for you, but I still stand by the fact that the video card is problematic, and not the power supply.

I honestly think you're better off trying to RMA the card than the PSU, in my opinion.
 
The S12-500 could handle TWO 7900s assuming they were functioning properly to begin with.

Video cards DO NOT draw large load until you start playing a 3D game. Artifacting before then == Definately not amperage problem. Unstable rails could cause it, but you'd likely also experience system lockups first. And since you aren't...

Your witnessing heat/voltage induced accelerated electron migration. RMAing your PSU is going to be a waste of both yours and Seasonic's time and money.
 
Maybe I gave the wrong impression... I have no intention of sending back this Seasonic PSU. It has worked FLAWLESSLY for the past 6 months, even when I played with overclocking alot harder than I am now. I agree that the vid card is the problem. I was just trying to provide some info for other Seasonic users...basically that Seasonic is telling me that the 6 pin connector *can* supply 22A of 12V current. This simple fact should take the PSU out of the video card manufacturer's argument entirely (i.e it is NOT the PSU)... No, the RMA business will be on the video card end - that or this thing goes back to NCIX for a refund, and my trusty old (aka WORKING) 6600GT goes back in for a while.

Thanks for the support folks,
A
 
Closing thoughts:
Got the card working properly without RMA-ing anything. In my case, updating the A8N32 bios to 1205 (which is the version when 7900 support is officially documented) seemed to do the trick. Initially didn't work because the overclock of the system board and RAM wasn't fully stable. Since then, I've ironed out the details, and all overclocking of the system (not the vid card) works again.

...one reason to run linux?...this card ALWAYS worked under linux...never a single artifact. Makes me wonder how the OS under linux interacts with the MB BIOS at boot-time, compared with Windows (which couldn't handle the 7900GTX until the MB was updated.)
Cheers,
Adrian
 
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