How important is the 12v connector to motherboard operation

[lchyi]

My friend called me up recently and said his computer won't work (he's building one). When I got there I saw that his power supply doesn't have a 12v connector (that 4 pin thing next to your NB usually). So I told him that it should still boot up even though its not connected. He has a GA-8SQ800 and since it was a newer board, I figured that maybe it requires it. Older P4B533 boards and some Athlon boards don't require it I guess because mine doesn't and neither does a friend of mine (he's actually missing the connector from his PSU also). I don't know, I always have put it in mine, but one time I did forget and it still worked. Oh, other symptoms are that, though everything is plugged in, none of the CD-ROM/RW drives and hard drives are spinning, nothing but the processor and northbridge fan power up. I'm just curious if I have a dead motherboard or it's his power supply not giving enough juice to everything.

 

[bacillus]

on a p4 board that 12V connection must have power.
you should be able to get an adapter for your normal psu molex plug if his psu doesn't have one.

 

[lchyi]

Kay thanks, just to clarify... as in "must" does that mean it will boot up and not run correctly or it won't do anything whatsoever?

 

[spoondigity]

It won't boot. It will spin the fan for a second each time you try but it stops.

 

[DAPUNISHER]

Modern Intel and AMD CPUs draw power from the 12v line and the extra 12v connector when present is necessary since the board is designed to provide power through it. Some boards like my Asus supply a 4 pin molex connector in addition to the 12v one for use with older PSU's. You can get an adapter for his PSU to allow you to use the 12v connector here's one

 

[Mark R]

The extra 12V connector (if fitted) does not always have to be used. It depends on the motherboard design.

Intel's recommendation is that CPU power should be derived only from this 4 pin connector. Failing to connect this connector will result in no power reaching the CPU.

However, many AMD motherboards, simply connect this connector directly to the 12V lines on the ATX connector - this way the load is spread through both connectors. In this case, if the 12V connector is left disconnected the system will still work perfectly, although the ATX connector may get hotter than with it.

 

[Jeff7]

Originally posted by: DAPUNISHER
Modern Intel and AMD CPUs draw power from the 12v line and the extra 12v connector when present is necessary since the board is designed to provide power through it. Some boards like my Asus supply a 4 pin molex connector in addition to the 12v one for use with older PSU's. You can get an adapter for his PSU to allow you to use the 12v connector here's one

Cheaper.

 

[Mark R]

Some boards like my Asus supply a 4 pin molex connector in addition to the 12v one for use with older PSU's. You can get an adapter for his PSU to allow you to use the 12v connector <a class=ftalternatingbarlinklarge href="http://www.colorcase.com/chanyourpows.html" target=new><FONT face=Tahoma color=#000080>here's one</FONT></A>

There is the problem that disk drive connectors are only rated for 8A. A P4 could potentially take more than this - this is why the 4 pin square design was chosen, it can carry 18A. The disk drive connectors also have a considerably higher resistance (25 mOhm compared to 5 mOhm) with subsequent reduction in power quality.

 

[lbmcleod]

some athlons dont require it to be plugged, just spreads power, but p4s require it