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Power Supplies

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3 replies to this topic

#1 Albert Frankenstein

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Posted 27 July 2006 - 08:25 AM

Is it normal to have a power supply with a bad -5v leg? Can you still use it? Will modern computers work without this leg?

I have noticed many new power supplies that I have purchased lately have a bad -5v power leg, according to my little power supply tester. However, conducting my little survey I have seen some Dell power supplies on a known good computer test bad on the -5v leg also - but like I said the computer works just fine.

I just received a brand new $100 power supply, should be a good one, right? Plugged in the tester and shows a bad -5v leg.

What up with this? Is this ok nowadays to use?


Currently home chillin' with the fam and my two dogs!

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#2 ddeerrff



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Posted 27 July 2006 - 10:09 AM

What are the specs on the supply? Looking at some of the currently available supplies, some of them do not have a -5 volt output, and those that do have only a minimal current rating (.3A) on that leg.

I don't believe modern systems use that voltage anymore. But I'm not a hardware expert......

#3 Albert Frankenstein

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Posted 27 July 2006 - 10:16 AM

Thanks for responding.

What you say is absolutely true in my mind too. But I don't know for sure.

I buy cases with power supplies in them, kind of cheap ones. Lately they all test bad for the -5v leg. I have been throwing them away. It occured to me that maybe I don't need the -5v leg as this new expensive 500W power supply tests bad for the -5v leg, too, and I wouldn't expect this power supply to be bad right out of the box.

So, on the cheap power supplies I get, it does show that it should put out 0.3a on the -5v leg. But my tester flags it as bad.

On the new 500 W power supply there isn't even a -5v leg! I have just installed this power supply in a new expensive build and everything fired up just fine!

How many power supplies have I thrown away that I could of used? :thumbsup:

Currently home chillin' with the fam and my two dogs!

#4 just me

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Posted 27 July 2006 - 12:09 PM

Albert Frankenstein:

I'll let you interpret the following (I personally assume that the -5 Volt lead is no longer in the specifications for an ATX12V power supply):From page 3:

Version: 1.2
Release Date: Jan, 2002
• Typical Power Distribution. Change +5V loading on all power
supplies distribution tables defined in DG to 0.3A
• PS_ON# Add text “The power supply should not latch into a
shutdown state when PS_ON# is driven active by pulses between
10ms to 100ms during the decay of the power rails.”
• Remove –5V from all power distribution tables.

Version: 1.3
Release Date: April, 2003
• Update Power and Current guidance
• Added efficiency guidance at typical and light load
• Increased min efficiency at full load from 68% to 70%
• Serial ATA* connector definition added
• Acoustic levels added for low noise power supply design
• Reformat and update revision table
• Update Disclaimers
• Remove guidelines for ATX
• Remove guidance for –5V rail
• Updated guidance for Energy Star and stand by efficiency

Version: 2.01
Release Date: June, 2004
• Updated 3.3 V remote sense pin # on the main power connector
• Updated 12V2 DC Output Noise/Ripple information
• Removed -5V reference
• Updated 5Vsb maximum current step

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