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Computer keeps blowing out -5v rail

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February 10, 2011 3:29:20 PM

My computer quit working, so I checked power supply. The -5v rail was dead. I changed power supply with new ocz 500. After two weeks the -5v rail is now dead on new ocz. What would cause this?

More about : computer blowing rail

a c 248 ) Power supply
February 10, 2011 3:36:56 PM

The -5V rail isnt dead, its not present. Nothing in a modern system needs it and it was dropped from ATX spec a while ago, you will notice on the 24 pin main connector there is one spot with no wire connected to it, thats where the -5V used to be, but since its no longer used modern PSUs dont even generate it since they have no where to provide it to.
February 10, 2011 4:09:25 PM

I have heard that, but the only tester I have is an older 20 pin tester. When I use it on my backup power supply which is a generic 24 pin, I get all lights green. When I use it on the ocz or the original power supply it does not light up the -5v. When I first bought the ocz to replace the original I tested it and the -5v did light up?
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February 10, 2011 4:58:29 PM

Could a bad motherboard cause the power supply to quit? I know my tester could be giving me bad info, but somthing is causing my power supply to quit.
a c 248 ) Power supply
February 10, 2011 6:35:15 PM

The OCZ really shouldnt have had a -5V rail, all ATX spec after and including ATX 12V 1.3 published in april of 2003 have prohibited the inclusion of a -5V rail, so i would blame your tester as being bad, not the PSU. List the other parts in your system and describe its symptoms as best you can, i dont think the PSU is the main thing at fault here, its time to look for other culprits.

Also, even if you did kill the -5V rail and the -12V rail, your system would still run fine, they were used for offsets to send output signals on older style connectors, not for the actual functioning of the system.
a b ) Power supply
February 10, 2011 11:58:23 PM

most new psu's dont even have a cable going to -5v, just an empty pin on the motherboard power connector....its not used anymore. look at your connector, i bet there is no wire going to -5v.
February 11, 2011 12:32:30 PM

Can you use a +5vsb power supply in place of the old -5v in my computer? I have not changed anything else in my computer.
February 11, 2011 12:59:19 PM

hunter315 said:
The OCZ really shouldnt have had a -5V rail, all ATX spec after and including ATX 12V 1.3 published in april of 2003 have prohibited the inclusion of a -5V rail, so i would blame your tester as being bad, not the PSU. List the other parts in your system and describe its symptoms as best you can, i dont think the PSU is the main thing at fault here, its time to look for other culprits.

Also, even if you did kill the -5V rail and the -12V rail, your system would still run fine, they were used for offsets to send output signals on older style connectors, not for the actual functioning of the system.


The system is:
Biostar t-Force 6110/ 24 pin power
Sempron 2.0
2x512 DDR
160 gb HD
ANTEC CASE W/400WATT PS
DVD BURNER
FLOPPY DRIVE
512 MB PCI-EX VIDEO CARD (ADDED AFTER POWER SUPPLY CHANGE)

I got the computer from my uncle. He said it would not boot. I checked the power supply with my old tester, it showed all green except the -5v. I hooked up my spare power supply and it booted up. The only thing that seemed wrong was the video was fuzzy with lines running across the screen. I ordered a ocz 500 power supply and a pci-ex video card. I replaced the power supply and added the video card. It booted just fine, I reloaded all software and all was good.
I then took it back to my uncle, and it worked fine for 2 weeks. Then it would start but no video. I had him send it back to me. I again tested the power supply and it showed the same results as the antec had, no -5v light. I hooked up my spare power supply and the computer booted with video just fine.
Something is messing up the power supply`s? I have ordered a new power supply tester with 24 pin testing abilities.
I am leaning toward the motherboard being the problem, since the video was going out when I first got it. The backup power supply I am using to test with is a generic 585 watt with 24 pin power.

Any Ideas! Thanks Jmcconnaha
!