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PSU - New PSU not working with old Mobo

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July 25, 2010 3:40:00 AM

I bought a VX550W Corsair PSU to replace what seems to be a dying (i.e. intermittent freeze and restarts) Allied Model: AL B450E PSU on an old K7 Triton 400 Series Mobo. With the new VX550W Corsair PSU the system will POST and then will usually reach the windows logon screen but rarely any farther (sometimes desktop for a few minutes) in the boot process. So I tried the old, but seemingly bad, PSU and it will act as usual (PC usable, sometimes for days, but intermittent freezes and shutdowns). So with the new VX550W Corsair PSU the only difference is the system shuts down unexpectedly more consistently (usable for only minutes instead of usable for days with the old PSU). The only thing I can find on this is that the newer PSU might have a minimum amp drawing requirement on one or all of the three rails. Also, the old PSU does have a -5V rail and the new one does not (ATX12V Ver 1.3 revision I believe) but it seems this -5v rail was used for ISA boards and is no longer needed because PCI does not require it, at least that's what I have been told. Any help on whether or not the new PSU is combatible with my old motherboard would be appreciated.

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July 26, 2010 12:25:54 AM

Thanks for the reply,
System specs (Old) :) 

Mainboard : MSI MS-6712
Chipset : VIA KT400 (VT8377)
Processor : AMD AMD Athlon XP 2100+(palomino)
@ 1733 MHz MUlitplier: x13 - Bus Speed: 133MHz - FSB: 266MHz
Physical Memory : 2304 MB
DIMM1 1024 MB Kingston DDR333 PC2700 (166 MHz)
DIMM2 1024 MB Kingston DDR333 PC2700 (166 MHz)
DIMM3 256 MB Nanya Technology DDR333 PC2700 (166 MHz)
Video Card : NVIDIA GeForce FX 5200
Hard Disk : WDC (120 GB)
Hard Disk : WDC (300 GB)
Network Card : VT82C570 MV IDE Controller VT6102 Rhine II
Operating System : Microsoft Windows XP Professional 5.01.2600 SP3
DirectX : Version 9.0c


It's interesting that you purport an issue with my comment ("IT is not amperes...it is wattage") but do not explain in detail to the misconception. What I had read, if true - which I was not aware of, is that some PSU's have a minimum load (i.e. - e.g. The +12V rail needs to draw 2 amps which would = 24 watts) that each rail needs to bear in order to function properly. This was my first question. My second question was, whether that particular power supply works with that particular motherboard in regards to the -5v line missing on the P1 connector 20th pin (18th pin on old PSU) on new PSU. Which I think I already have the answer to. So, if what you're responding to in the comment is to the statement that this load-bearing necessity is true (which was my question), then wattage and amperes would both be correct. For instance, if PSU stated that the min. was 20 watts on the +12V rail (which would be an odd way to state a spec for a PSU, amp draw would be more relative to the rails) then comparatively this would be a draw of 1.66 amps. So please elaborate on your terse response and if possible answer the compatibility question. Thanks in advance.
October 8, 2010 6:08:50 PM

Sorry for such a late response on my results. I'm a little perplexed at what is happening with this thread though. Someone responded and now that comment has been removed (as you can see from my reply it wasn't much help, but still odd that it no longer shows). Anyways, to whom it may help, I contacted the maker of the new PSU (VX550W Corsair) and they stated that there is a min. amp draw on each rail (not wattage draw as the guy who commented so adamantly stated "Can't let you do that, It 's not amps its Wattage", then some how the comment was erased which now makes me look like I’m talking to myself :sol:  ). What I ended up with was a dell PSU (from a Dimension 5150) on the old Mobo (MSI K7 Triton 400, this has been working consistently for months now :)  ). This 5150 PSU was similar in that it did not have a -5v rail like the new VX550W Corsair PSU (the original one, AL B450E PSU, that wasn't working had a -5v rail) so it definitely was not a compatibility issue with the -5v rail missing. So the only obvious differences from the VX550W Corsair PSU and the Dell Dimension 5150 PSU is the min. amp draw and the amount of available amps on all three rails (mainly the 12v rail). I forget to state that the VX550W Corsair PSU was not just DOA, it has been working in an old Dell dimension 8300 for a few months also( ironically the dimension 8300 is around the same age as the MSI K7 Triton 400, but yet it works). Hopefully this will help some random PC user down the road. Any comments would be appreciated.
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October 8, 2010 7:06:54 PM

the psu is too different for that age of a machine you gonna have to get an atx12 spec 1.3 psu the best of which is the zippy emacs 300 watts
October 10, 2010 7:49:14 PM

Thanks for your reply. As you can see from the previous posts it was a bad PSU and has been resolved. I wasn't sure if I was supposed to mark this thread as solved. I originally thought the compatibility issue was the age of the Mobo vs the ATX version (as you were stating) but this same Newer PSU (VX550W Corsair) actually worked in another Mobo of comparable age (not the same model but same year, circa 2002 - Dell Dimension 8300) so it seems it's a combination of Mobo compatibility (chipset) and ATX version, not just one or the other.
Thanks again for the reply, far better then the one I received earlier that now has mysteriously vanished :heink:  .
Resolved.
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