# ATX 20 Pin vs. ATX 24 Pin power connection



## Amkus_XIII (Oct 20, 2004)

I am curious, what is the difference between the ATX 20 pin connection and the ATX 24 pin connection. (Besides the fact that one has more pins  ) I have aquired an MSI 915P NEO2 Platinum motherboard. The board has a 24 pin socket, but the manual says you can use either. I am having a problem with the system and am wondering if this may be the cause. I am using a PCI Express video card and I am getting no video. The system appears to be posting everything sounds like it is spinning up, but no video. I am not getting any bios beeps / tones telling me there is a problem. The monitor knows that there is something there, but it is just a blank screen. Any suggestions? 

System:
MSI 915P NEO2 Platinum
LGA775 3.0 GHz Pentium 4
1x 512 mb DDR2 533 MHz 
1x CR-RW
1x 36 gb WD360 10k Hard Drive
XFX PCX5750 PCI-Express Video Card
Raidmax Power Supply 420W


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## quizme1220 (Sep 21, 2004)

*ATX 20 Pin vx ATX 24 Pin power connection*

Read this: http://www.melecom.com.au/Motherboard Power Connectors.htm


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## Amkus_XIII (Oct 20, 2004)

Hello, Thanks for the link it explained things pretty well. I also found through trial and error that the PS was not my problem. It was a bad Mother Board. The interesting thing was that the MB could take either plug and the manual said you could use either. I don't understand that. If you don't need the extra power why put in an interface for it. If it is needed why say it's optional. :4-dontkno Oh well, I already bought a new Power supply, and I got an RMA for the board. Thanks again for your help.


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## Katanaman (Oct 22, 2004)

*ATX 24 Pin Problem i.e.No -5 Volt Supply!*

I have an Antec TruePower 550 watt PSU. It has one of these new 24 pin plugs on it unfortunately. I say unfortunately as it does not appear to supply the output voltage -5 volts like the label on the side of it says it does. 

I have checked the outputs with a multimeter and nowhere did I measure -5 volts. Only 3.3, 5.0, -12 and 12 volts. 

I made this discovery when..

1. I bought an OCZ DDR Booster device that uses a 20 pin PSU socket for the PSU's motherboard plug to plug into. The OCZ DDR Booster device's cable then goes on to plug into your motherboards socket. The booster has several wires that branch off from the usual 20 pin PSU wires, including a white wire for -5 volts. Of course with a PSU that uses a 24 pin socket, you must first use a convertor to change it from 24 to 20 pin and then plug in the OCZ DDR Booster. A lot of plugs and potential voltage drops. (Not good).

2. I bought an adapter to change a 24 pin PSU motherboard plug to a 20 pin one, for older (most) motherboards. I noted that the white wire used for -5 volts on my other PSU and on this adapter went to a position on the 24 pin plug from the Antec TruePower 550 PSU that had no wire going to it at all.

I compared my Antec TruePower 550's (24 pin) wiring with my Antec TrueControl 550's (20 pin) wiring and it seams that I can only use my OCZ DDR Booster device with my TrueControl PSU. I did not expect this.

My first impression was that someone in the Antec factory may have omitted to install the -5 volt wire accidentally on my TruePower 550 PSU.

Can anyone confirm this please?


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## MD_Willington (Jan 11, 2005)

Who/what device actually uses the -5V and -12V ?

Most modern boards don't use them. They are hold overs for boards that power devices on the Serial comm ports. Since most serial comm ports are defunct or not that great on mainboards, or are removed entirely, people that require such comm ports use an add on PCI card with serial ports and the power for those devices is derived from the PCI slot.

PCI bus pinout
http://www.interfacebus.com/Design_PCI_Pins.html

MD


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