Case Short

[Hardline]

Hello,

I have a Dynamax case (my favorite) I am trying to build a
system with. The case seems to be shorting out my new motherboard. Can
I place the motherboard on rubber washers (1 or 2) below the mounting
screw holes to elevate it a little? Will this cause a problem such as
melting of the rubber or any other issue? Any advice would be
appreciated.

Thanks!

 

[Matthew Hicks]

You can use rubber or the traditional plastic standoffs that most
motherbaords ship with. The processor will die long before any rubber or
plastic melts.


---Matthew Hicks

 

[Paul]

Hello,

I have a Dynamax case (my favorite) I am trying to build a
system with. The case seems to be shorting out my new motherboard. Can
I place the motherboard on rubber washers (1 or 2) below the mounting
screw holes to elevate it a little? Will this cause a problem such as
melting of the rubber or any other issue? Any advice would be
appreciated.

Thanks!

The motherboard has tinned rings around each mounting point. The
tinned rings are grounded. The brass standoff on the computer
case is also at ground potential. The purpose of the contact
is to help reduce EMI (electrical noise). The standoffs ground
the motherboard to the chassis.

The motherboard is also grounded through the black wires on
the main ATX power connector. So if you insulate the standoffs
it is not the end of the world. The black ground wires on the
main power connector, provide a return path for power currents,
so insulating the standoffs should not prevent the thing from
working.

The I/O plate also has springy metal fingers, and those metal
fingers help ground the metal boxes around the I/O connectors.
Again, the purpose of that contact is for EMI containment. It
is supposed to prevent electrical noise from leaving the computer
case. (Well, that is the theory at least.)

On my computers here, most of the electrical noise they generate
(hash lines on the TV set) are caused by conducted emissions on
the power cable. Inadequate filtering inside the power supply is
the reason.

Now, what is the problem with adding washers ? It upsets the
placement of PCI/AGP/PCI Express cards in their slots. If
you lift the motherboard with wsahers, it rests higher than
normal. I/O cards, once their faceplates are screwed down,
will be sitting on an angle in their slot connector. If the
angle is great enough, either pins won't make contact, or the
wrong pins will make contact. You don't want that.

To prevent shorting, try to position the motherboard so it is
centered over the mounting points. Shorting can be because of a
couple of reasons. A standoff with an excessively large diameter,
might come in contact with something on the motherboard. Or
screws or washers could contact something on the surface of
the motherboard.

I would first try a thorough visual inspection, to try to figure
out what is going on, before I'd try washers. If you try washers,
you'd want to compensate on the height of the standoffs as well,
if this is going to be a permanent solution.

And if the case isn't cutting it, replace it. Sure, it may look
cute, but if the computer doesn't work, you've got nothing but
a big door stop

Paul

 

[Shep©]

The motherboard has tinned rings around each mounting point. The
tinned rings are grounded.

But they are not electrically connected to the motherboard
cicuitry(thank god) =)

 

[Paul]

But they are not electrically connected to the motherboard
cicuitry(thank god) =)

I grabbed my spare motherboard here, and measured from an I/O connector
screw (easy to put alligator clip from my multimeter), and the rings are
connected to the same ground as the I/O screw. There is no reason to use
conductive metal there, unless an electrical connection is desired by
the designer.

Get your ohmmeter out and give it a try.

In this doc:
http://web.archive.org/web/20060105234350/http://www.formfactors.org/developer\specs\matxemc.pdf

"It is suggested that ground contacts be made via the ground pads
at the mounting holes that are defined in the microATX Motherboard
Interface Specification."

Now, the versions of "microATX Motherboard Interface Specification" I
can find, make no mention of mounting point design. I cannot find a
keepout spec or anything else. But it must be in one of the specs.

In this one, on the last page of the checklist:
http://www.formfactors.org/developer/specs/matxchk1_1.pdf

"Motherboard mounting features provide grounding"

There does seem to be a reason for them to be grounded. Despite
what some other web sites claim. It is part of electromagnetic
compliance (EMC) design.

Paul

 

[Shep©]

I grabbed my spare motherboard here, and measured from an I/O connector
screw (easy to put alligator clip from my multimeter), and the rings are
connected to the same ground as the I/O screw. There is no reason to use
conductive metal there, unless an electrical connection is desired by
the designer.

Get your ohmmeter out and give it a try.

In this doc:
http://web.archive.org/web/20060105234350/http://www.formfactors.org/developer\specs\matxemc.pdf

"It is suggested that ground contacts be made via the ground pads
at the mounting holes that are defined in the microATX Motherboard
Interface Specification."

Now, the versions of "microATX Motherboard Interface Specification" I
can find, make no mention of mounting point design. I cannot find a
keepout spec or anything else. But it must be in one of the specs.

In this one, on the last page of the checklist:
http://www.formfactors.org/developer/specs/matxchk1_1.pdf

"Motherboard mounting features provide grounding"

There does seem to be a reason for them to be grounded. Despite
what some other web sites claim. It is part of electromagnetic
compliance (EMC) design.

Paul

You are course correct however if you check around the mounting holes
you will see that they are not part of the motherboard circuitry and
don't want to be as this would change the potential of the board and
is a common cause of board failure.The motherboard circuitry does not
want to be grounded through these points.
I've had to fix systems where the motherboard has been badly installed
and the screws have chaffed into the circuit thus grounding the board
at this point.
I also have had boards that have bowed over age or were that way from
the shop and grounded underneath to the case.I always fit the foam
rubber that comes with new board under the board to help prevent this.

HTH

 

[Hardline]

Thank you!

You are course correct however if you check around the mounting holes
you will see that they are not part of the motherboard circuitry and
don't want to be as this would change the potential of the board and
is a common cause of board failure.The motherboard circuitry does not
want to be grounded through these points.
I've had to fix systems where the motherboard has been badly installed
and the screws have chaffed into the circuit thus grounding the board
at this point.
I also have had boards that have bowed over age or were that way from
the shop and grounded underneath to the case.I always fit the foam
rubber that comes with new board under the board to help prevent this.

HTH

 

[Rod Speed]

You are course correct however if you check around the mounting holes
you will see that they are not part of the motherboard circuitry and
don't want to be as this would change the potential of the board and
is a common cause of board failure.The motherboard circuitry does not
want to be grounded through these points.

He has just pointed out that when you test it with a multimeter, the
motherboard is indeed designed to be grounded at the mounting holes.
It it wasnt, you wouldnt get a low resistance between the IO connector
screws and the solder land around the mounting hole.

I've had to fix systems where the motherboard has
been badly installed and the screws have chaffed
into the circuit thus grounding the board at this point.

Separate matter entirely to the motherboard which
have a large solder land around the mounting hole.
It isnt even possible to 'chafe into the circuit' with those.

I also have had boards that have bowed over age or were
that way from the shop and grounded underneath to the case.

That shouldnt happen when all the available mounting holes are used.

I always fit the foam rubber that comes with
new board under the board to help prevent this.

Thats not a good idea either.