Strange Power Supply Behavior - 20/24 pin Oddity

Matt0717 · 05-20-2007, 05:17 PM

I'm having a very strange problem building my new rig.

I've been building computers for many, many years and this is the first problem I've ran into that has me stumped. I figured I would ask here before starting to buy replacement parts, which is really the only option I have left.

The motherboard in my new system is an Asus A8X-S, which requires a 24-pin power connection because of the PCI-E x16 slot on it. The power supply that came with my case is a 450W no-name generic power supply. Not my first choice, and I'll replace it if I have to, but it should at least get the system powered up, right? Well, not yet...

First of all, the 4-pin 12v connector for the CPU is plugged in, I didn't miss that.

The power connector for the main 24-pin socket comes out of the power supply as a 20-pin and a 4-pin. They are separate connectors.

When I originally hooked everything up, the system was completely dead. The only thing that would come on was the green light on the motherboad that detects presence of power. However, hitting the power switch did nothing -- no fans, no HD spin... nothing.

So, I did some research on the ASUS support forums and one of their tech support reps had posted a message that stated even if the motherboard has a 24-pin connector, you can still just use a 20-pin power supply and everything should work fine. (Only later did I realize that the extra 4-pin is to power the pci-e slot... but read on)

So through process of elimination I ended up with only the 20-pin connector plugged into the mobo, and the 4-pin not connected to anything (remember, through all of this I DID have the 12v CPU 4-pin lead plugged in). Well, with only the 20-pin connected, the system powers up... fans spin, HD spins, DVD-RW drive lights up, etc.... but of course I have no video because the pci-e slot is not getting its 12v power.

But (and here's the stumper) when I plug in the additional 4-pin power adaptor to the remaining 4 sockets on the 24-pin connector, the whole system becomes dead again. Power button does nothing, no fans, no HD spin.... just that little green light on the mobo that detects presence of power. If i remove the 4-pin from the 24-pin connector, I'm back to everything being fine except no video.

Now, when you connect the 20-pin and the 4-pin to the 24-pin connector, you really have to shove the 4-pin connector hard to get it to fit. It squeese VERY tightly against the 20-pin. My only hunch (albeit a minor one) is that perhaps the 4-pin is so tight that it is causing the 20-pin to lose contact with the socket. I am thinking about shaving some plastic off the 4-pin to that it fits a little easier.

What the heck is going on? Is there something wrong with the 4-pin plug from the PSU that is "overloading" the mobo, causing it to not power up? Do you think the 24-pin connector on the mobo is bad??

My next step will be to buy a new power supply with an actual 24-pin connector on it, instead of a separate 20 and a 4. After that, I guess mobo replacement will come next... but I thought perhaps someone here could shed some light on the problem.

Thanks in advance,

Matt

**linderman** · 05-20-2007, 05:59 PM

99% of PSU's that come with a case a major league JUNK

unless the case and power supply were $200.00 ????????????

is the four pin connector that feeds the cpu power have two yellow wires and two black wires ?????

cutting or slimming the 20 plus four plug wont help and the 20 + 4 is the most common psu connector today!

your problem is the cpu power and the video 4 pin power are shared on the same rail or orgin in the PSU

and its just plain insufficient power capability.

The good thing that case and PSU combos do well is raise the cost of shipping. UPS and Fed-X like that

you should seek at least an Antec 650 watt Trio Power they are decent at newegg for about $120.00 ish

or OCZ 700 watt @ tigerdirect.com for about $99.00 ( i prefer the antec)

**speedster123** · 05-20-2007, 07:01 PM

Joe is 100% on this, and personally, I wouldnt mess with that power supply anymore before you damage your board. good luck

Matt0717 · 05-20-2007, 08:43 PM

Thanks for the feedback folks; I'm not messing with that piece of junk anymore... I will pick up a new supply and hopefully all will be ok.

Thanks again

05-20-2007, 05:17 PM	#1 (permalink)
Matt0717 Registered User Join Date: Nov 2004 Posts: 3 OS: Windows XP SP1	Strange Power Supply Behavior - 20/24 pin Oddity I'm having a very strange problem building my new rig. I've been building computers for many, many years and this is the first problem I've ran into that has me stumped. I figured I would ask here before starting to buy replacement parts, which is really the only option I have left. The motherboard in my new system is an Asus A8X-S, which requires a 24-pin power connection because of the PCI-E x16 slot on it. The power supply that came with my case is a 450W no-name generic power supply. Not my first choice, and I'll replace it if I have to, but it should at least get the system powered up, right? Well, not yet... First of all, the 4-pin 12v connector for the CPU is plugged in, I didn't miss that. The power connector for the main 24-pin socket comes out of the power supply as a 20-pin and a 4-pin. They are separate connectors. When I originally hooked everything up, the system was completely dead. The only thing that would come on was the green light on the motherboad that detects presence of power. However, hitting the power switch did nothing -- no fans, no HD spin... nothing. So, I did some research on the ASUS support forums and one of their tech support reps had posted a message that stated even if the motherboard has a 24-pin connector, you can still just use a 20-pin power supply and everything should work fine. (Only later did I realize that the extra 4-pin is to power the pci-e slot... but read on) So through process of elimination I ended up with only the 20-pin connector plugged into the mobo, and the 4-pin not connected to anything (remember, through all of this I DID have the 12v CPU 4-pin lead plugged in). Well, with only the 20-pin connected, the system powers up... fans spin, HD spins, DVD-RW drive lights up, etc.... but of course I have no video because the pci-e slot is not getting its 12v power. But (and here's the stumper) when I plug in the additional 4-pin power adaptor to the remaining 4 sockets on the 24-pin connector, the whole system becomes dead again. Power button does nothing, no fans, no HD spin.... just that little green light on the mobo that detects presence of power. If i remove the 4-pin from the 24-pin connector, I'm back to everything being fine except no video. Now, when you connect the 20-pin and the 4-pin to the 24-pin connector, you really have to shove the 4-pin connector hard to get it to fit. It squeese VERY tightly against the 20-pin. My only hunch (albeit a minor one) is that perhaps the 4-pin is so tight that it is causing the 20-pin to lose contact with the socket. I am thinking about shaving some plastic off the 4-pin to that it fits a little easier. What the heck is going on? Is there something wrong with the 4-pin plug from the PSU that is "overloading" the mobo, causing it to not power up? Do you think the 24-pin connector on the mobo is bad?? My next step will be to buy a new power supply with an actual 24-pin connector on it, instead of a separate 20 and a 4. After that, I guess mobo replacement will come next... but I thought perhaps someone here could shed some light on the problem. Thanks in advance, Matt

05-20-2007, 05:59 PM	#2 (permalink)
linderman Moderator, Hardware Team Join Date: May 2005 Posts: 20,437 OS: win 2000 pro / Win XP pro My System	Re: Strange Power Supply Behavior - 20/24 pin Oddity 99% of PSU's that come with a case a major league JUNK unless the case and power supply were $200.00 ???????????? is the four pin connector that feeds the cpu power have two yellow wires and two black wires ????? cutting or slimming the 20 plus four plug wont help and the 20 + 4 is the most common psu connector today! your problem is the cpu power and the video 4 pin power are shared on the same rail or orgin in the PSU and its just plain insufficient power capability. The good thing that case and PSU combos do well is raise the cost of shipping. UPS and Fed-X like that you should seek at least an Antec 650 watt Trio Power they are decent at newegg for about $120.00 ish or OCZ 700 watt @ tigerdirect.com for about $99.00 ( i prefer the antec) __________________ I still know nothing and I respect that fact, striving to improve and, along the way, help anyone that comes from the place that I used to be! Power Supply Selection LEARN TO BACK-UP YOUR DATA FREE & EASY YouTube - Runtime Software DriveImage XML tutorial

05-20-2007, 07:01 PM	#3 (permalink)
speedster123 Mentor Join Date: Oct 2006 Location: United States-New York-Long Island Posts: 5,219 OS: xp pro SP3	Re: Strange Power Supply Behavior - 20/24 pin Oddity Joe is 100% on this, and personally, I wouldnt mess with that power supply anymore before you damage your board. good luck __________________

05-20-2007, 08:43 PM	#4 (permalink)
Matt0717 Registered User Join Date: Nov 2004 Posts: 3 OS: Windows XP SP1	Re: Strange Power Supply Behavior - 20/24 pin Oddity Thanks for the feedback folks; I'm not messing with that piece of junk anymore... I will pick up a new supply and hopefully all will be ok. Thanks again