I just bought a new power supply Corsair CX430 V2 in order to meet the needs of a new graphics card I hope to install. The motherboard is the micro-ATX form factor Asus P5KPL-AM/PS running a Intel C2D E7200 CPU and 2x2GB of DDR2-800 RAM.

Problem: the computer doesn't boot with the new PSU.

The case Power LED turns on alongwith the PSU and CPU fan for about 3-4 seconds before switching off. The comp. works just fine with the current PSU which is a local brand 400W conforming to ATX12V1.3. The new PSU works fine with three other motherboards: two AMD-based ones and one old Gigabyte LGA775 board running a P4 HT chip.

On my motherboard, the following combinations were tried with no success:
1)20+4 pin connector plugged in; each half of the 4+4 ATX 12V connector plugged in, by turn.
2)20 pin connector plugged in; each half of the 4+4 ATX 12V connector plugged in, by turn.
3)20+4 pin connector plugged in; the 4+4 ATX 12V connector not plugged in.

In the above attempts, no other peripherals or add-on cards were present.

With the old PSU, the 20+4 as well as the CPU 4-pin connector is plugged in.

My dealer-engineer is blaming it on motherboard compatibility but that doesn't seem to be the issue.

The motherboard manual on p1-28 says, "we recommend that you use a power supply unit (PSU) that complies with ATX 12 V Specification 2.0 (or later version) and provides a minimum power of 400 W.". The new PSU, as per the manufacturer, "is backward compatible with ATX12V 2.2 and ATX12V 2.01 systems".

Any suggestions on what the issue may be or how to proceed next?

  • It's pretty bizarre, but here's a thought - have you tried it with the motherboard outside the chassis? Maybe something is grounded improperly and the old PSU is more tolerant of it than the new one. This is a REALLY weird problem, though - if it were me I'd honestly just return that power supply and get something else. Corsair is usually fairly good, though I've only really used their high-end stuff. – Shinrai Jan 19 '12 at 16:27
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    My dealer tried a 3rd PSU (one of his own) and that worked with my mobo. – Gyan Jan 19 '12 at 16:32
  • Only one half of the split 2x4 ATX power connector should fit in the 2x2 socket due to the connector/socket being keyed; so you're scaring me. ;) – Ƭᴇcʜιᴇ007 Jan 19 '12 at 17:49
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    I've read elsewhere that Corsair doesn't follow the Spec to the tee, so that either half should work. – Gyan Jan 19 '12 at 18:53
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    See here – Gyan Jan 19 '12 at 19:00

The biggest problem is different manufactures produce power supplies with different amounts of amps on each voltage. The main ones are 3v,5v, and 12v. On a 400w or 430w PSU if you 5v has 50A then the 12V is going to have a low number of amps.

We don't know what your "New video card" is, but chances are a higher watt power supply would make your problems go away. The specs say your new PSU only has 28A on the 12v supply.

The 400w psu may have more amps on the 12v channel and less on the 5v and therefore it worked.

However to avoid all this non-sense get a 550w or 600w psu and you will have enough amps on all voltages.

  • Since you missed it, there were no add-on cards installed when I tested the PSU, so the card doesn't come into it. Also, during startup, even a heavy duty graphics card doesn't draw much power. And finally, the new power supply is successfully and uneventfully being used in another computer, since then. – Gyan Apr 2 '13 at 17:11

I am not sure if this applies in your situation, but, in my case, the reason the Corsair PSU would not remain powered on turned out to be that the load placed on the PSU was "not large enough".

Corsair apparently designs their PSUs this way as (I'm guessing) a fail safe?

Or at least they did. Since your question (and mine) are now over 7 years old, I have no idea how a current Corsair PSU would work. But this certainly appears to be how it works for my now elderly Corsair CX430 430w PSUs.

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