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Low -12V and -5V

Last response: in Systems
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January 29, 2011 6:39:34 PM

I have a system here which has been experiencing low voltage on the -12V and -5V. -12V is running at -7.74V and -5V is running at -4.74V. I replaced the 450W PSU which was about 5 years old with a brand new 550W power supply. I thought that was the problem, but I'm still seeing the same volts.

Here's the specs.

Mobo: Gigabyte TA790GXB A2+(I'm running most recent BIOS version)
Video Card: Gigabyte HD 4350(most current ATI drivers)
Memory: OCZ Reaper HPC Edition 4GB DDR2 800
Windows 7 Professional 64-bit
Processor is running stock speed, no tweaks.
See attached JPEG for rest of hardware.



Any ideas why my voltage would still be so low?

More about : low 12v

January 29, 2011 7:34:45 PM

How are you measuring the voltage? Just from the looks of it 550W is big enough to power your system. Please list the brand and model PSU you bought. 7.74V is way to low on the 12V side and 4.74V is also out of spec. Here is a link to the CPUID Hardware Monitor (http://www.cpuid.com/softwares/hwmonitor.html).
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January 30, 2011 3:47:36 AM

Your PSU is fine and working as it should. It is the +12 and +5 values that are important here. The -voltages are not used by the system.
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January 30, 2011 4:40:55 AM

The -5 and -12 rails are seldom used these days. Some serial port's controllers still use the -12v line to generate the offset, but that's basically all that uses it, and even then some modern controllers don't need it supplied externally now and can generate it internally. The -5v rail was used back in the ISA days by some ISA cards and floppy controllers, but it's been unused for over a decade. The -12v is still in the PCI standard and is present on a pin in the standard PCI connector, but as far as system function, you could lose both of them, and probably never know it.
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January 30, 2011 5:45:42 PM

OK, good to know.

I thought I had power problems because sometimes the screen will just randomly go black and the computer acts like it's locked up. I've verified it's not the monitor or the video card by testing with a second monitor and onboard video. System is clean of malware.

After the screen goes black, the only way I can get the computer to do anything is to shut off the power switch on the PSU and start it back up.
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January 30, 2011 5:58:14 PM

With a hard lock like that it's sometimes hard to pinpoint the issue. Are you doing anything in paticular when this happens or is it completely random?

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January 30, 2011 7:30:42 PM

Often this can be caused by a services conflict or driver conflict. You might try to shut down all but required windows services and see if the issue goes away. If it does then you need to start them one by one to find the culprit. The fact that the screen goes black does suggest a hardware issue. Your task now is to verify each piece of hardware by disconnecting or removing and reinstalling. If all proves good then start to look at a software cause. You might check the windows event log to see if an exception occurred. GL
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January 30, 2011 9:44:26 PM

mavroxur said:
With a hard lock like that it's sometimes hard to pinpoint the issue. Are you doing anything in paticular when this happens or is it completely random?


The computer will do it at any time. Idle, surfing the net, playing music, streaming to XBox. It's totally random.

Dogsnake said:
Often this can be caused by a services conflict or driver conflict. You might try to shut down all but required windows services and see if the issue goes away. If it does then you need to start them one by one to find the culprit. The fact that the screen goes black does suggest a hardware issue. Your task now is to verify each piece of hardware by disconnecting or removing and reinstalling. If all proves good then start to look at a software cause. You might check the windows event log to see if an exception occurred. GL


Thanks for the advice. I'll give that a whirl.
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January 30, 2011 11:55:26 PM

Normally a black screen normally isn't memory related (though ive seen it before), but you might start off with a good memtest86 test and verify that first, since it's the easiest.
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February 3, 2011 4:38:58 AM

I disabled my Daemon Tools and Ad-Aware, system has been up and running for 2 days now, no problems. I'm guessing it's my Daemon Tools messing it up, with it's virtual CD-ROM driver. Will have to look into this more as I need to have a virtual drive for mounting ISO's. Might just use a different program like Virtual Clone Drive.
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December 1, 2011 12:06:06 AM

I'm bringing this thread back from the dead. System hasn't been up and running for months because I got sick of messing with it and I use my laptop alot anyways.

Screen still randomly goes black, even on a fresh install of Windows. Does it in Safe Mode too.

I've verified the memory is good and I've tried testing with nothing more than the motherboard, CPU, 1 stick of memory and system HDD installed.

Still randomly reboots.

Starting to lose hair......
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December 1, 2011 12:22:13 PM

Your PSU could be giving out noisy/dirty power, which would cause random issues too. Can you try another PSU?
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December 1, 2011 12:49:54 PM

mavroxur said:
Your PSU could be giving out noisy/dirty power, which would cause random issues too. Can you try another PSU?


I have tried another PSU, no change.
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December 1, 2011 2:50:57 PM

what about your power source??? is it on a really old breaker.....a crappy power surge protector??? or worse,,, an extension cord?!?!


in your hw monitor screen shot it looks like your vrm's hit'n 90c??? was this an aberration or has it repeated that temp???


have you visually inspected the board.....a blown cap could act like that... here is a link to what one could look like

http://www.ccl-la.com/badcaps.htm

i had that happen on an older P4 sony vaio.....each successive lockup reboot came quicker and quicker
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December 8, 2011 7:39:12 PM

The power source is not an issue. I have recently moved to another apartment and the issue is still there.

The 90 degrees C is a false reading.

I have not inspected the board, will do so.

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