In the process of putting together a P 4 motherboard which is straight forward the only thing I am concerned about the mounting holes to the chassis. Should they be insulated from the chassis frame. Using a ohms meter all mounting holes to LPT1 body zero ohms on both sides of the board with the motherboard on the benchtop not in a box. These mounting holes are they suppose to be isolated.
Sam
If they were, woudln't they be that way by design?
No, frame should be earthed.
-mark
Thanks for your replies. I have found more information on the net (see below) but even if I was to isolate the mounting holes one thing I noticed the IO ports metal frames would contact the chassis and there is a circuit between the IO ports and the mounting holes rings while the board on bench.
Sam
First thing could be a shorting out issue while the board is installed in your case. The easiest way I have found to remedy this situation is to use those little red paper washers between the mounting studs and the bottom of your motherboard. You also want to make sure that you dont have any extra mounting studs installed that could be shorting out the underside of your board. Each mounting stud should have a corresponding hole in the motherboard.
Why the hell shoudln't it be earthed? Theyr all obviously designed that way .. the chasis itself is earthed via the powersupply casing (hence you attach an antistatic wrist strap to the casing, to give it a discharge path) As you said, not only do the legs touch this, so do the back panel IO connectors, and if you look at some of your PCI/AGP cards, i'll bet you'll find theres a good chance some of those may well have theyr back plane connectors connecting to earth .. Why bother with little red things if everything else in the case is still going to contact?
Have you had a good look at the board? Does it look like its a mistake? That ALL your mounting holes are somehow connected, and that also connects to the IO ports? Thats one hell of a fluke ..
From memory, those little paper washers (which, incidentally, are no longer included with most motherboards), date back to the days of older computers (386, etc) and was more to prevent touching of active motherboad solder pins touching to the earth connections, than it was to stop an earth contact.. have a look at how much the lead solder points stick out on a modern board vs an old 386 board.. there was a much greater chance of something bad shorting out..
The comment regarding mounting studs lining up with teh holes is just plain common sense, and irrelevant to thinsg being grounded or not ..
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