New build won't POST when case fans are connected to PSU

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henry.p.mckay

Nov 12, 2018
4
0
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I just built a new gaming PC using mostly new parts, see parts list here.

The case has 3 built in fans that all run to a fan control switch on the front of the case, which then connects to a 4-pin molex connector. When I connect that molex to the PSU (using a 6-pin PCI-E adaptor), the whole thing won't POST. It will briefly start up, the fans will start to spin for a fraction of a second, then shut off, no beeps.

If I disconnect the fans from the PSU, then the computer will run fine, though the GPU and CPU will get too hot quickly during gaming without the case fans running, of course.

Any idea why this is happening? My PSU is a few years old. Can I instead connect the case fans to the sys_fan connection on my mobo? What kind of adapter would I need?

 
Solution
feelinfroggy777
Gotcha, most mobo's have multiple fan headers. Looks like yours only has one. There may be an issue with the switch or the molex adapter.

I would try using a SATA adapter since molex is old tech. Below is a link to a SATA to fan header adapters. You would just hookup one of your SATA cables from the PSU (the power cables hooked up to SSD/HDD) to the adapter. Then run your fans through each fan header.

https://www.amazon.com/Computer-Power-Connector-Y-Splitter-Adapter/dp/B01LVY5S50

If that does not work, then you may have an issue with your PSU.
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feelinfroggy777

feelinfroggy777

Glorious
Dec 13, 2016
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45,990
There may be an issue with the molex adapter or you may have an issue with your PSU. You can try running your case fans through the motherboard, the should be three pin connections and you don't need an adapter to run the fans straight through the mobo.

But if you do have an issue with your PSU, running your fans through the mobo may not be the best idea as a malfunction could potentially damage your system. You don't have a terrible PSU, but it is not the best in the world either.
 
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henry.p.mckay

Nov 12, 2018
4
0
10


It looks like each fan has its own 3 pin connector. These connect to a cable that has multiple female 3 pin connectors that then goes on to connect to the fan control switch on the front of the case. I assume this is so all fans can be powered through the switch and then through the single molex adaptor via the PSU. I don't see how I could connect all 3 fans to the single sys_fan port on the mobo. Would I need some kind of splitter to do this?
 
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feelinfroggy777

feelinfroggy777

Glorious
Dec 13, 2016
5,721
135
45,990
Gotcha, most mobo's have multiple fan headers. Looks like yours only has one. There may be an issue with the switch or the molex adapter.

I would try using a SATA adapter since molex is old tech. Below is a link to a SATA to fan header adapters. You would just hookup one of your SATA cables from the PSU (the power cables hooked up to SSD/HDD) to the adapter. Then run your fans through each fan header.

https://www.amazon.com/Computer-Power-Connector-Y-Splitter-Adapter/dp/B01LVY5S50

If that does not work, then you may have an issue with your PSU.
 
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Solution
H

henry.p.mckay

Nov 12, 2018
4
0
10


Thanks for your help so far! I will try a SATA - fan hub connector and see if that works. I can use one of those female SATA connectors that is midway along the SATA cable going to one of my SSDs, right? That's essentially a splitter?

I'm a bit bummed to lose the easy fan control offered by the case switch, but I'm beginning to suspect that the switch is the real culprit here.
 
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H

henry.p.mckay

Nov 12, 2018
4
0
10


LOL, I bought this one because it's cheap and I figured, "what could go wrong with something as simple as a case?"

I guess I learned my lesson!

UPDATE: I purchased the SATA to fan header adapter and connected the fans to one of the SATA cables running from my PSU to one of my SSDs. The fans now run beautifully and don't short the whole computer. For everyone's reference my Cougar - MX330 ATX Mid Tower Case has a switch on the front to control the fans. The case fans are meant to connect from the PSU through this switch. But the switch seems to be faulty and prevented my computer from even turning on when it was connected to the PSU. Bypassing the switch solved the problem.
 
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