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I'll start by apologizing for asking another question on a topic which obviously pops up over and over and over again. I tried to locate an existing answer matching my situation, but I did not. If you know of an existing question/answer, please point me towards it.

I have two Intel DG45ID motherboards which failed to power up with minimal components installed when I use my Corsair CX430 430w power supply. By "minimal components I mean only the CPU & 1 stick of DRAM & the PSU were installed. When I switched on the Corsair PSU both the processor fan and the PSU fan spun for a few seconds and then they both stopped. No beeps from the on-mobo speaker. The power switch has no effect.

I have tested the PSU using this Rosewill Power Supply Tester and the tester thinks everything is copacetic.

Because the tester was happy it wasn't until the second motherboard failed to power up in exactly the same way as the original that I decided to try another power supply. After I swapped the Corsair PSU for an Antec Earthwatts EA-380 380w PSU, the motherboard powered up OK. (I haven't tested a complete boot yet, but the fans spin up and mobo beeps at me ... presumably because I don't have any input/output devices connected yet.)

Corsair's instructions for testing their PSU seem to boil down to connecting a case fan via a molex connector then shorting the green and black pins on the 24-pin connector and see if the fan spins up. Because I seem to find shorting two connectors too challenging, I changed this to connecting a case fan via a molex and then connecting the 24 pin PSU connector to the PSU tester. Both the case fan and PSU fan spun up fine and, once again, the tester was happy with the voltages.

Yet there must be something wrong someplace since the mobo won't power up unless I use a different PSU.

Is it possible for a PSU to have failed and yet still test as OK? How can this be?

Update:
It wasn't until after posting that I noticed the question New Power Supply doesn't work with a specific motherboard in the "Related" questions list on the right hand side of this page. My reading of the question is that the poster also had a CX430 fail with a specific, though different from mine, motherboard. Hmmmmm.

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  • It is possible to have a power supply with too many amp in the wrong place and still be higher watts. The working one has 32amp@12v and the non working one has 28amp@12v. This could be the issue.
    – cybernard
    Commented Aug 30, 2013 at 1:55
  • When only the CPU and one stick of DDR2 RAM are installed? I would think 28A is more than sufficient for that configuration. Also, the label on the "working one", the Antec 380w, says its 12v lines are rated at only 17A.
    – irrational John
    Commented Aug 30, 2013 at 2:08
  • The 380w has 2 independant 12v channels 17A is only one of them. It has another 18A channel at 12v for a total of 35A.
    – cybernard
    Commented Aug 31, 2013 at 5:02

2 Answers 2

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What you describe makes it seem like you forgot to plug in your ATX 4-pin 12V supply (it can be 8-pin for 2 lines of 12V, depending on your motherboard) for the CPU. The socket for this is usually placed near the CPU socket.

Both CPU and PSU are fine, but not having that 12V supply will cause the system run up for few second and then auto power down (it can automatically start up again and then down, and so on)

Update: Your motherboard has a 4-pin socket, located at "I" on page 11 of your motherboard manual.

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  • Thanks, but I am afraid that is not the problem. I check and then double check that the 4-pin connector (for a DG45ID) is plugged in. Perhaps the CX430 does not enable the 12v on the 4-pin connector "fast enough" to make the DG45ID happy? OF course, I don't know of any way to investigate a wild guess like that.
    – irrational John
    Commented Aug 30, 2013 at 1:22
  • described? or descries?
    – Griffin
    Commented Aug 30, 2013 at 3:44
  • @irrationalJohn Ever concidered the wire is messed up?
    – Griffin
    Commented Aug 30, 2013 at 3:44
  • @Griffin The thing is, just as in the other question I add the link to in my update, the Corsair CX430 works fine with other motherboards. It only seems to have a problem with some motherboards in particular. My Intel DG45ID and (apparently) the Asus P5KPL-AM/PS. If there was a simple wiring error I don't think it would work at all. I'm not sure what this is.
    – irrational John
    Commented Aug 30, 2013 at 6:13
  • @irrationalJohn I'm not saying that I'm saying the inside of the wire. Like it's cut on the inside.
    – Griffin
    Commented Aug 30, 2013 at 23:00
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The problem ultimately turned out to be a "feature, not a bug" situation. (Another way to characterize it is, "I'm an idiot!" 😳)

I eventually learned that there is circuitry in a Corsair PSU that will shut it down if the load on the PSU is "not large enough" when the PSU is turned on. This is why the Corsair PSU would shut down when I attempted to power on a very lightly loaded mobo and why this did not happen when I used the Antec Earthwatts EA-380 PSU.

I also had no problem using the Corsair PSU if I connected an additional load, e.g. a hard drive, to the PSU.

Since I allowed so much time to pass before posting this answer, I can't point to the specific post from a Corsair person in another venue who explained this. But essentially I was expecting the PSU to work in a situation where it was not designed to.

In hindsight this makes complete sense to me. But at the time I could not get my mind to see what was actually happening. Not the first time an unfounded assumption made a fool of me. Probably won't be the last either. Drat.

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