An odd mobo problem

The magic smoke.

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An odd mobo problem

Postby Widget » Fri Nov 02, 2007 2:44 pm UTC

Howdy all,
So I'm working on putting together a new system in what free time I can finagle, and have hit what I think is a bit of a curious problem. In its original state, this problem caused the green power LED on my board never to activate. I thought it might be a bad power supply (since the one I got came with the case and was a bit of a cheap one). Replacing the power supply didn't fix the problem, though, so I chalked it up to a defective board and started the RMA process with my vendor. I unscrewed all the mounting screws and was about to take it out when I figured, what the heck? and tried giving it some juice one more time. To my excitement, the LED turned on this time. It turns out that there was one screw that, when in place, caused the LED to turn off. I took out that screw and tried powering up the system with only CPU, video card, and power supply connected. The system made a very odd sound and didn't do much of anything. So, I figure it worked last time, why not try it again? I took out all the mounting screws and gave it some juice, sure enough the fans started spinning.

Here's the fun part: I went through trying to figure out which screw was causing issues this time around. I place screw one back into position and try giving the board some juice. As soon as I throw the switch, I am given the opportunity to find out exactly where the CMOS materials are located inside a certain IC package as it becomes red hot and proceeds to bid farewell to the majick smoke that we all know and love so well. Removing the screw and giving the board power again brought about the same results as before- the fans kicked on (though still no board beeps and whatnot).

So my question is what could have caused this? Obviously something high voltage was shorted to something low voltage, but how? My guess is either:
1) The mounting platform of my case somehow got shorted to something it shouldn't have
2) Pressure from the screws combined with a defect in the board caused a voltage line in one of the layers to be forcibly connected to a ground layer line in a layer above or below
3) It was assumed that some sort of non-conductive washer was to be placed between the board and the mounting screw and this caused the screw to short something on the board to ground.

Any ideas? For reference, links to the board and case are as follows. ... 6811192024 ... 6813131025

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Re: An odd mobo problem

Postby Larson » Fri Nov 02, 2007 5:50 pm UTC

It's hard to say, but I'd guess it was some combination of your first 2 ideas. Most boards are designed with blank areas around each screw hole, hopefully preventing option 3.

The only related thing I've seen is when a friend of mine attached his motherboard directly to the case without the mounting standoffs. All sorts of strange behavior ensued.

I'm not much of a help, but the manufacturer should still take the board back for RMA since it could just have easily been a defect.

edit: Welcome to the forums :)

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