computer motherboard

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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



Re: computer motherboard


If they were, woudln't they be that way by design?


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Re: computer motherboard


No, frame should be earthed.

-mark



Re: computer motherboard


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.


"mark jb" <nukeleer at internode dot on dot net> wrote in message
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Re: computer 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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