ATX harnessing

[Marbles_00]

In peicing together a new HTPC, I have a supply with a 20-pin Molex but my MB has a 24-pin header. Looking at my MB manual indicates the additional 4 pins are +12V, 3.3V, 5V and GND. I was going to assume that I needed a 20 to 24-pin adapter. That was until I was looking around and found a slightly different version of MB manual to what I have, which indicates that I can plug the 20pin Molex into the 24pin header and disregard the 4 additional pins (connectors are keyed so unless a bang it with a hammer, I won't be plugging it in incorrectly). Does anyone know what those additional voltage lines are for? Are they just for sharing voltage drop/current draw? Or are they actually supplying a bunch of seperate circuits? The Board is a MSI K9N Neo...but this header is universal so the circuitry should be standard across MB manufacturers.

Thanks for any insight.

[P3rv3rt B3ar]

im not anykinda authority on the matter, but afaik theyre just for providing some extra juice for modern powerhungry boards. and i think there are adapters which let u ruote regular 4 pin drive connector to those xtra four pins.

EDIT: allthough i have no idea where u get 3.3 in that configuration mayby its not suplied with one of those...

[P3rv3rt B3ar]

Disregard what i just said... i think i managed to confuse CPU 12V power cable and and those 4 extra pins on 24 pin cable ... seems i been too long away from building comps

[Marbles_00]

Yeah its distictively 3.3V (for supplying some micros of some sort). I wouldn't connect a drive cable adapter direct to those four pins that's for sure. Well, for the <$10.00 for an adapter harness...even though I suspecting it is just additional lines to help in current consumption, I may as well get one...at least I know then I won't be risking a $100 on a blown MB...just because I don't want to waste needlessly.

These boards are crazy as it has an additional 4 pin Molex to supply the CPU with +12V...and it is 2x12V lines plus 2 returns. Don't recall the wire guage, but even at 18AWG, there's close to 5A max carrying current capability right there. This is my first with these CPU's (AMD AM2 socket 939)...amazing how much juice they want.

And for anyone who really cares...the 24-pin ATX breakdown:



Pin Name Color Description
1 3.3V Orange +3.3 VDC
2 3.3V Orange +3.3 VDC
3 COM Black Ground
4 5V Red +5 VDC
5 COM Black Ground
6 5V Red +5 VDC
7 COM Black Ground
8 PWR_OK Gray Power Ok is a status signal generated by the power supply to notify the computer that the DC operating voltages are within the ranges required for proper computer operation
9 5VSB Purple +5 VDC Standby Voltage (max 10mA)
10 12V Yellow +12 VDC
11 12V Yellow +12 VDC
12 3.3V Orange +3.3 VDC
13 3.3V Orange +3.3 VDC
14 -12V Blue -12 VDC
15 COM Black Ground
16 /PS_ON Green Power Supply On (active low). Short this pin to GND to switch power supply ON, disconnect from GND to switch OFF.
17 COM Black Ground
18 COM Black Ground
19 COM Black Ground
20 -5V White -5 VDC
21 +5V Red +5 VDC
22 +5V Red +5 VDC
23 +5V Red +5 VDC
24 COM Black Ground

[PhilB]

this guy on ebay sells all types of adapter cheap if you feel you need it.

http://stores.ebay.com/powersupplycables

I bought from him in the past without issue.

[cooldog]

Go ahead and give it a try. If you've got sufficient power supply, and do not have the most power-hungry CPU and RAM that the board will take, you'll probably be just fine.

It is the closest thing to certain that you will not damage anything even if it doesn't work. In this case, "doesn't work" will most likely mean "isn't stable".

If you run into stability problems, you might even try temporarily *underclocking* the CPU until you can get a replacement power supply.

I've done all this before ...