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3.6v on 3.3v rail

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May 24, 2011 10:13:29 PM

I've recently had problems with my computer turning on. Suspecting the PSU, I grabbed a DMM. And began checking the pins. On all my connectors, the 5V and 12V were within the 5% tolerance (were ~5.1v and ~12.44v), but my 3.3v line was running at ~3.6v (tolerance up to 3.465v). Is this much of a difference enough to cause my problems? I've already spent more money fixing this problem than I'd like to and I want to be sure before dropping the cash on a new PSU too.

Thanks,

- Matt

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May 24, 2011 10:20:28 PM

I doubt it. I always thought it was +/- .5v tolerance? What brand power supply are we talking about?
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May 24, 2011 10:27:22 PM

It is a Rosewill 950W that I got back in '07. The ATX spec stated a +/- 5% on all but -5DC and -10DC.
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May 25, 2011 12:12:41 AM

The tolerance (± 5 % ) for the + 5 V is based on the Min/max voltages for TTL logic chips.
For the +12 V, voltages below 11.4 make the CPU voltage regulators on the MB work harder and can over heat. For this reason I use 11.6 V for a Min on the +12V. Slightly above the 12.6 (ie up to 12.8 V) is normally OK.
The +3.3 V use to be used for the Ram, but newer systems (past couple of years) use the +12 V (Could also use the +5)to step down to the required DIMM voltage. So I'm not really sure whate the 3.3 is used on current systems (I've heard that some of the Newer HDDs may use it - have not confirmed but voltage is included on SATA power connectors.) The 3.3V line is also used for the 1.5V AGP voltage (Again this was for older systems). Some PSUs do not provide good regulation when the current is below what the manuf is expecting and may be the reason it is out of spec.

You didn't mention which MB/system you have so it's hard to say. The +10 % on 3.3 is Probably Not a problem (in itself). UNLESS your MB is infact classing it as Over voltage and not allowing the "I'm OK" signal



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May 25, 2011 12:18:11 AM

I have a EVGA 750i FTW motherboard, 2x Crucial Ballistix 2GB 1066 MHz RAM, Intel Quad Core 2.67 GHz, and an ASUS 480 GTX. I've also got a DVD burner and 3 HDDs.
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May 25, 2011 12:39:09 AM

In the case that it's not the power supply, I have posted a thread with a more thorough background of the issues over in Homebuilt Systems (http://goo.gl/gCyrI).
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January 17, 2013 6:43:39 AM

so something similar to this is happening to me, although it is under voltage, my ASUS Utility warns me at 2.952 V on my +3.3v rail. when watching it when it is not sending me warnings it stays around 3.1-3.0 voltage. any ideas?

here are my computer specs:
ASUS 990FX Sabertooth Motherboard
AMD 1055T X6 2.8GHz
Raidmax 730w Power Supply
Western Digital 1TB HDD 7200rpm 3Gb/s
OCZ Agility 3 60GB SSD 6Gb/s
XFX Radeon HD6870 Graphics card
Creative Sound BlasterZ Sound Card
Coolermaster Storm Scout Case
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