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PSU modifications

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August 14, 2012 7:10:08 AM

Hey guys, it's my first post on these forums. Didn't think i'd need to join these, but I think it'll be nice to have a little help on something every now and then.


Anyways, I have a PSU from say, 2004. I need to be able to use it to test fans and other components.
It's not really good for anything but this. I already have PSUs for my other computers. This one doesn't even have
SATA power, just the old 4-pins.

I plug it in, and y'know that big connector that goes straight into the motherboard? I found 2 pins on it that I connect with a jumper, and I am able to run a nice little fan.

However, the fan runs much slower than if I am to plug the big cable into the motherboard, and turn the motherboard on. I want to fix this so that it goes full speed when I just use jumpers on the big cable.

Theres also the fan on the back of the PSU -- it does not run, I see that as a problem. Any help on this?

More about : psu modifications

August 14, 2012 7:34:32 AM

connecting the fan with a 3pin molex connector to a motherboard is going to regulate the speed of the fan. Connecting it that way will let the motherboard automatically adjust the fans rpms based on defined temperature settings or you can set the speed of the fan manually by percentage.

connecting fans via the 4 pin molex gives you no power control and will run at full speed all the time.

look at the picture below and let us know what connector your fan has

link to very high resolution photo of the above connectors http://t3.gstatic.com/images?q=tbn:ANd9GcR6p8_jUgVKL1Ko...

you can replace the fans on your psu, just buy a replacement fan of equivalent size (old psu fans are probably going to be 80mm) and you are probably going to have to cut the bad fan positive and negative wire and solder the new fan to those wires. All the psus i've been inside don't use a standard 3/4pin connectors, usualy just a 2pin red/black cable.
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August 14, 2012 7:57:17 AM

As I stated previously, I'm looking to run this without a motherboard.


Yes, I have a 4-pin.
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August 14, 2012 8:30:24 AM

i don't see where the problem is

if you have a 4pin molex fan connect it to one of the 4pin molex connectors from your psu and short pins 14&15 of the 20/24pin main harness. doing this will make the power supply turn on/run without the need of any additional computer hardware.

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a b ) Power supply
August 14, 2012 8:35:09 AM

Short a 20 pin (big connector) with a jumper or paper clip so it turns on.
Then you have power on all connectors.

Use adapter from molex (4pin old style) to 3 or 4 pin fan to power up your fan at full speed.

You can do that yourself, just connect red wire (12v) and black (ground) from molex to fan connector.

Have a look here:
http://img.techpowerup.org/110517/pwm_diagram.jpg

Edit: PSU fan may be not turning on because of low load.
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