Old Power Supply Mod on new system. Making my own 4pin ATX connection

[itguy]

I have a homebuilt system that uses a 24 pin power supply connector plus the 4 pin power connector that is near the cpu. The problem is my modern power supply has failed and I'm trying to get an old style 300w (20 pin connector and no 4 pin connector for the cpu) power supply to work.

When I plug in the old power supply everything lights up but I can't get into the bios. This is most probably because my motherboard also requires power from the 4 pin connector near the CPU and this power supply is too old to have that connector.

Anyone know of any guides or mods that show you how to provide power to the 4 pin area and thus allows an old 20 pin power supply to be used in the newer motherboards that also need a 4 pin plug? Anyone hear of this working?

Thanks.

 

[hunter315]

You should NOT do that. The PSU will die catastrophically if you try it, it does not have the 12 Volt capacity to handle a modern system that requires a 4 pin ATX plug.

$40 and 3 days will get you a good small PSU that will be usuable for several years, i really, really, really, do not suggest modding the old PSU to get it to run a modern system.
http://www.newegg.com/Product/Product.aspx?Item=N82E16817139008

 

[itguy]

I hear what you are saying, but hear me out. The 4 pin connector is simply 2 yellow 12 volt leads and 2 black ground leads, correct? So all I have to do is cannabalize 2 of my hard drive power connectors and I will get 2 yellow 12 volt leads and 2 black grounds. Then I just splice those 4 wires correctly onto the 4 pin connector that I harvested from the broken power supply. Then I should have the right power going to the right area Albeit I will have less power connectors to connect other devices like CD roms and extra hard drives but I have enough power connectors left over where it doesn't affect me. Should work, no?

Tell me if I have made an error in thinking please.

 

[itguy]

Update. Completed the mod. It is working like a charm. Feel free to duplicate if you find yourself in a similar situation.

 

[False_Dmitry_II]

Tell us when your old power supply loses the magic smoke due to being overworked.

 

[itguy]

Wow, You guys sound like Cheney's false speculation on what imminent doom would happen to America if we didn't attack Saddam's (fake) WMDs. In the end it was all just lack of information and fear driving the wrong decision.

The older psu's and newer ones are the same products with different plastic connectors except the larger wattage ones can handle more devices and high powered graphics cards. It won't overwork a 300watt psu to run 2 dedicated 12 volt leads to the ATX pin and power up a basic system of 1 hard drive, dvdrw, dual core proc, and low watt graphics card which is what I am running on this machine.

So far, I've proven that it works. Now it's your turn to prove that it doesn't.

 

[hunter315]

Older power supplies powered older systems primarily with 5V and 3.3V power, modern systems get 80% of their power from the 12 volt rail, an older PSU without a 4 pin connector has about 2/3rds of its power on the 5V and 3.3V rails and will not support a modern CPU for long, and certainly not a graphics card. Yes the power is getting delivered but that doesnt mean its not bringing the PSU very close to its danger point. What are the specs of the system you are running on that PSU? I really suggest you upgrade your PSU or you may end up experiencing this first hand.
http://www.corsair.com/cinema/movie.aspx?id=622747

 

[itguy]

Cute vid. The ironic thing is that the psu that fried was a "modern" (but piece of junk like in the vid) 420watt psu that had the ATX connector and was rated at 420watts (cough-liers). I've now switched it out for a heavy, quality made old school 300watt psu and I have much more confidence in the one I just put in. I'll try some stress testing and do some light gaming on it now.

Specs: Athlon 64 X2 4400+, AM2 board, 1.5 gb ram, geforce 7200 512mb.

 

[False_Dmitry_II]

That might actually be okay. The real test would be to run furmark AND prime95 for a couple of days. If it doesn't die after sustaining a load like that, it might take a while.

 

[4745454b]

7200? Try it with something that needs a PCIe plug.

The older psu's and newer ones are the same products with different plastic connectors

Wrong. As hunter said the older ones are designed to power from the 5 and 3.3V rails. It probably has 8A of power on the 12V rail. Enough for the CPU, not enough for a real card.

 

[Onus]

...
The older psu's and newer ones are the same products with different plastic connectors except the larger wattage ones can handle more devices and high powered graphics cards. It won't overwork a 300watt psu to run 2 dedicated 12 volt leads to the ATX pin and power up a basic system of 1 hard drive, dvdrw, dual core proc, and low watt graphics card which is what I am running on this machine.

So far, I've proven that it works. Now it's your turn to prove that it doesn't.

Wow. I'm just glad that this sort of ignorance (which we all once had) is easily cured by the simple application of knowledge.
If hunter's explanation and the further remarks from 4745454b didn't convince you, go to www.hardwaresecrets.com and read their articles on PSU anatomy. Hopefully in the meantime your PSU will not have suffered the fate of the chokemax PSUs from that video.

 

[False_Dmitry_II]

Unless the PSU takes out everything else when it dies, I don't see why we really care about it. It being older and him obviously having no other use for it; it's not like it's a huge loss if it goes under and he has to buy something else, right?

 

[4745454b]

Mostly correct False. There is a chance when it dies it could pass a power spike to the mobo killing it, but that's not a given. With the 7200 I would run it, but only until my new PSU arrives. I'm not rich enough to replace broken equipment, so I'm a bit picky about my PSUs. (running all modern Antec PSUs here.)

 

[Onus]

Same here. I have neither money nor time to waste like that, so I'm also using Antec.