majestykelf

Hi. First post here. I am a computer tech of many years experience, but I've got a computer on my bench here that is freaking me out.

In short, the machine came in due to a suspected bad power supply. I unplugged the power supply's main plug from the mobo and plugged it into our tester. No lights, so presumed bad. I took a testing power supply and plugged it into the mobo just to see if the machine would power up. As per usual procedure, I plugged a keyboard/mouse/monitor into the machine. Hit the power switch, and everything powered up. I let it run on, expecting it to quit when it got to checking for the hard drives or the OS because they were still plugged into the 'dead' power supply. To my surprise, the machine went ahead and booted into Windows.

Okay...I thought it might be because the four-pin plug from the 'dead' power supply was still plugged into the mobo, so I unplugged that and plugged in the four-pin plug from the testing power supply. Hit the power button...machine still booted to Windows desktop.

At this point, to be clear, I have the following situation:

1.) 'dead' power supply plugged into the hard drives and DVD-burner.
2.) 'good' power supply plugged only into the main motherboard plug and the four-pin auxiliary plug.

So, we have no physical connection between the 'dead' power supply and the motherboard, and the testing power supply has no physical connection to the hard drives. Why the heck is the machine booting? I even notice that the fan and LEDs on the 'dead' power supply are firing up, but I figure that's because of a separate fan header. Any ideas? I am at a loss, as are the four other techs who have looked at the system. BTW, the hard drives are IDE, and of course they ARE spinning up. I'm sure if I unplugged them from the 'dead' power supply the machine wouldn't boot, but I'm trying to figure out from where they are drawing power.

MONKEY BOY

umm maybye u have a loose conection for the atx plug for the motherboard on the 'dead' power suply ( im meaning inside the PSU box )

__________________
computer monkey

diduknowthat

Can you fire the "dead" powersupply up by using a pin to connect the green and black wires on the motherboard connector? It could be that just the motherboard connector cable it lose, damaged, or dead.

__________________

Dell Latitude XT Convertible Tablet
Intel Core 2 Duo U7600 1.2ghz CPU
3GB DDR2 677 Memory
120GB 1.8" PATA Hard Drive
ATI Radeon Xpress 1250 Graphics
12.1" WXGA LED Touch Screen
N-Trig Capacitive Touch/Active Digitizer