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Low voltage on 12v rail

Last response: in Components
a b ) Power supply
July 23, 2010 9:55:26 PM

I have a Compaq SR1130NX that was purchased in 2001. It shipped with Windows XP Home, and through the years the system has run Linux, FreeNAS, and finally Windows XP Pro. I added a second hard drive (IDE) and removed a CD drive as it stopped working. All hardware is stock and nothing overclocked. I've begun to notice that randomly, the PC will restart, and then would restart again upon the desktop showing up, and then would run slowly for about half an hour and then get back up to speed. This computer has had Windows XP Pro 32-bit installed for about a week, so it is a fresh install. However, a few hours ago, it restarted while browsing in Chrome, got to the desktop, restarted again, got the desktop again, restarted again, then only got to the Compaq BIOS Splash screen when it turned off completely. The system would not respond to the power button. The green light on the PSU was still on. I unplugged the PC and let it sit for a few hours, and plugged it back in and it started with no problems. I installed Everest Home to see if the computer is overheating, and here are the results:

Motherboard - 37C (99F)
CPU - 43C (108F)
WDC WD1600JB-22REA0 (Hard Disk) - 41C (106F)

At times the temps have gotten to 144F on load. These readings were at idle. I'm getting thermal paste tomorrow, but noticed something kind of odd. The Voltages read this:

CPU Core: 1.66V
+3.3 V: 3.34V
+5V: 4.95V
+12V: 11V
+5V Standby: 4.95V
VBAT Battery: 3.30V

The odd thing is the 12V rail, which I heard when this gets below 11 the system cannot boot. This number has gotten to 10.80 volts at some times when I've been watching the screen. The system has been running fine for now but it isn't under any load at all. There is no Video Card installed, and a 512 MB stick of RAM is installed, but that was stock (tested with MemTest86+, and it is OK). I'm wondering if it's time to get a new PSU and if that's causing the reboots and the shutdowns, because the CPU is really never above 50% load. I tried installing a wireless PCI Card, and the PC would never get past about 5 minutes after the desktop showed up before restarting. I use the system as a secondary PC currently, next to my new one and is running Synergy to act as a virtual KVM switch without the Video. I would also like to note that there is no fan on the chassis, but the side is kept open to allow air to flow through until I can get out to get a fan.


More about : low voltage 12v rail

a b ) Power supply
July 23, 2010 10:52:16 PM

A low +12v rail either indicates the PSU is being overloaded or a capacitor/voltage regulators in the PSU is own its way out.
a b ) Power supply
July 23, 2010 11:04:58 PM

Ok and I noticed that when I disconnected the second hard drive and the CD-ROM it stopped restarting, but I've had those components plugged in for years without issues. The green light on the PSU does dim when the power button is pressed, but then again, my new computer does the same, so I think I'll go buy a new PSU soon. I'll try the thermal paste first though as I'm not sure what the voltages were before this started happening. I'll give it a week with new thermal paste to rule out overheating..

But with those items disconnected it still reads 11V. I'll see if I can check the temps in the BIOS just to make sure Everest is reading them correctly.

EDIT: BIOS reads the CPU temperature as 82C (179F) and rising a degree about every 30 seconds, so I'm thinking this is more of a overheating issue than a dead PSU issue. At least now I know that this old PSU might be on it's way out.

PS. Just in typing this the temp has raised to 90C (194F) so I shut the system off to prevent it from burning up lol. I know that temp is WAY too high!