4 pin 12v PSU connector

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JamesE

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I am about to put together a new (simple) PC. The MB is a Biostar 6200, the processor is an AMD Sempron 2800+. The MB has a socket, which the book says allows 12v to be connected to the processor (??????). A modern PSU has such a 4 pin connector, two black, two yellow wires i.e. 12 volts. I want to use an old PSU which doesn't have the 4 pin connector. Is it necessary?
 

JohnWill

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YES IT IS! I doubt the machine will even power up without the connection. Also, any P/S that's old enough not to include the connector is probably not up to the task of running a modern system.

Do yourself and your system a favor, get a decent P/S.
 
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JamesE said:
I want to use an old PSU which doesn't have the 4 pin connector. Is it necessary?
If your board has the 4-pin "P4" plug, it probably requires it. So, Yes.

Can you get an adapter to let an older power supply work with a newer board? Yes.

Would I recommend it? New decent-quality power supplies are cheap, so No.

You are using a fairly low power CPU, so if your older power supply is of good quality (HEC, Antec, Fortron Source Power, etc) you'll probably be able to get away with using an adapter. Expect to spend $2-$5 mail order (+ shipping), $10-$20 retail.

A. Woolf
 

JohnWill

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I don't think I've ever seen an adapter for the 12V CPU supply plug for an old P/S, just the adapters to go between 20 and 24 pin P/S main connectors. In any case, any P/S that is lacking the CPU power plug probably doesn't provide sufficient +12V for a modern system.
 
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JohnWill said:
I don't think I've ever seen an adapter for the 12V CPU supply plug for an old P/S, just the adapters to go between 20 and 24 pin P/S main connectors. In any case, any P/S that is lacking the CPU power plug probably doesn't provide sufficient +12V for a modern system.
They were pretty common when the "P4" connector was new, but have pretty much faded away now that EVERY power supply comes with the 12V 4-pin plug.

Here are a few:
http://www.google.com/search?q=p4+power+adapter

A. Woolf
 

JohnWill

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Right you are, somehow I missed that in the transition. I guess I just bought the right supplies. :D
 

JamesE

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Thank you gentlemen - you have convinced me! I have ordered a new PSU (shame about the old one). The one I've ordered has a 20 pin connector and the MB is of course the normal micro standard with a 24 pin. As I understand it it doesn't matter - the extra 4 pins are simply doubling up of +5v (3wires) and ground. The adaptors convert the 20 to 24 but you don't really gain anything. As I mentioned at the start, this isn't a fancy machine, no video board consuming vast power!
 

JohnWill

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Glad you came to a decision.

You can mark your own threads solved using the thread tools at the upper right of the screen. :)
 

JamesE

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Well! Just for devilment! I completed the build this afternoon (UK time), installed XP and what had to be, had dinner and came back and played and unplugged the 4 pin 12v connector. It makes no difference whatsoever!!

I think it may be a Pentium thing but why Biostar put it on a socket 754 board I know not.

Well chaps! Comments??
 

JohnWill

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The 12V gives a low impedance path for the power to the switching regulator that supplies the processor power. When the processor is under full load, and other things are happening, I suspect you may well have stability issues without the proper connection.

They put that connection there for a reason.
 

JamesE

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Yes, I agree. The very fine copper track path from the normal socket might well show as too high an impedance - therefore the connector will be replaced. I didn't think though, that the AMD Semprons used 12 volts - can you enlighten me on this?
 

JohnWill

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I think if you look at any of the more modern systems, you'll see that the processor is supplied from it's own switching P/S on the MB, and it's supplied with 12V. Obviously, no modern processor uses 12V directly.
 
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JamesE said:
...unplugged the 4 pin 12v connector. It makes no difference whatsoever...
I seem to remember a few boards, including some from Biostar, that had the P4 12V right next to the 20-pin connector, wired in parallel with the 12V lines on the ATX connection.

With a board like that, as long as the 12V portion of the supply can supply enough current, the P4 connector is probably not needed. (But I'd still plug it in if it was my system....)

Here's a Biostar board (K8NHA Pro) configured this way:


A. Woolf
 
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