In article , "Patrick Martin"
wrote:

I just RMAed my two week old P4C800-E Deluxe M/B to NewEgg.Com because of
BIOS problems http://helpdesk.asus.com and I couldn't correct. Even after
updating to the latest BIOS version, I'd typically get "New CPU Installed"
alerts from the BIOS and have to manually reset BIOS data to get the M/B to
complete startup. ASUS was concerned about "EMI interference" and/or
improper grounding of the M/B to the case and suggested removing the M/B
from the case and test with just video card, and keyboard (no memory) on a
non-conducting surface (wooden workbench, phone book, or the box the M/B
came in) and if this worked reinstall in the case with electricians tape
over the metal M/B stand-offs and red-paper washers under the heads of the
ten screws that secure the M/B to the Lian-Li M/B tray. The system wouldn't
peep or show any life until I installed the RAM. After installing the
memory, it'd would fine and the BIOS retaining all the settings. The tape &
paper washers seemed to fix the problem (it'd regularly boot to XP w/o
incident) until I exchanged the newly assembled PC for my eight year old
200MHz machine. After hooking up things like the phone line, printer,
joystick to the game port, and an open-ended serial port cable, the new PC
would halt during POST with a "Black Screen". After a few cold reboots, I
got a display indicating the BIOS had again halted due to "CPU
Overclocking". The maddening thing is that the dam thing would again boot
to XP after removing the M/B tray from the case (M/B still bolted to the
tray), hooking up the internal stuff (power, HDD, floppies, PCI Modem, video
card, and CD-RW devices) and powering up. At that point I said "M/B latent
defect" and RMAed it back to the point of sale.

Is anyone else have any "EMI interference" and/or improper grounding problem
solutions they can share with us along with the workarounds?

Patrick

Grounding and emissions control (EMI prevention) on PCs for me are two
of the great mysteries. My first reaction to your post was "too bad the
Asus helpdesk didn't go into more detail about just what effect they
thought they were fixing", but because English is not their mother
tongue, I suppose it would be expecting a lot for them to go into more
detail.

Grounding is one of my weakness, in that I have a lot of trouble
identifying out of many theories, which one might be significant
enough to stop a circuit from working. Therefore, take the rest
of this meandering post with a "grain of salt".

First of all, Asus course of action sounds "doomed to failure". It is
my understanding that establishing the motherboard at ground potential
is important to the I/O function. In other words, if you expect to
connect external devices to your computer, this won't work reliably
unless the motherboard is well grounded. Now, "well enough" grounded
might mean that one or two standoffs minimum are conductors that short
the motherboard ground rings to the case metal.

In the case of the Lian Li, with slideout motherboard tray, the ground
path is not quite the same as it would be in a "cheap and cheerful"
steel riveted case. In a cheap steel case, it is easy to see how a good
ground can be established, as the motherboard tray is fastened to the
rest of the case. With a sliding motherboard tray, the metal
surfaces would have to be oxide free for good contact.

Another ground path is via the metal springs situated around the connector
area on the motherboard. These springs are there for the express
purpose of establishing a ground around the connectors. I've been
taught at work, that "EMI springs" are good for preventing RF leakage
around metal openings in a housing, but in the case of the PC, I think
the purpose might be for diverting external ground loop currents, so that
they cannot upset the ground potential inside the motherboard. For
example, say your printer is connected to a different wall outlet than
your computer. There could be a difference in the ground potential
between the printer and the computer. The cable to the printer is DC
connected, and communication relies on the ground reference at the
two ends of the cable not being very different. So, the ground path
from the green safety ground on the Power Supply, to the connector
shroud, is important to the printer cable and I/O working properly.

So, when Asus had you isolate the grounding on the motherboard, I
don't see that as being very useful to the end objective of having
a fully functional PC. Either the design works the way it was intended
or it doesn't, and in your case it isn't working.

Now, in terms of EMI prevention, everything I've been taught about it
is violated in the way that PCs are designed. Motherboards are typically
four layer microstrip design, with the conductor layers being
signal-ground-power-signal. The exposed signals on the top of the
motherboard function as tiny antennas, spewing interference into the
air. The proximity of the ground layer inside the motherboard, to
the signal conductors, helps attenuate the effect to a certain extent.
(In other words, if the board was just two layers signal-signal with
no ground, the motherboard wouldn't work and you wouldn't be able to
receive radio or TV broadcasts in your house, due to the electical
noise generated by the PC.)

The next layer of EMI prevention is done at the case level. A proper
RF proof case would be a "Faraday cage", a continuous metal cage with
no gaps in it, all around the device that needs protection. A PC case
has so many holes, bad metal to metal seams, etc., there is no way
a PC case can attenuate any kind of emissions.

I was taught that emissions and susceptability go hand in hand. Any
"antennas" inside the PC, can not only emit RF garbage out into the
air, they can also pick up garbage from other devices. You might see
the effects of this, if your PC crashes every time a noisy electrical
device is used nearby (vacuum cleaner motor, electric drill motor
etc).

So based on this small knowledge of grounding, I'm at a loss as to
just what Asus hoped to achieve by reducing the grounding. A solid
ground path is established through the COM signals on the 20 pin ATX
connector, so the motherboard can never be completely isolated. The
addition of grounding through the standoffs only serves to add
additional ways that return currents can flow back to earth ground,
and I would sooner leave those connected than disconnected.

I have no idea what kind of defect might exist inside that board.
It doesn't sound like anything digital is broken on the board.

If you have the time and patience, I'd try installing the motherboard
in a cheap steel case without a removable motherboard tray, just to
see if it would work in there. About the only thing I can think of,
is somehow the Lian Li is upsetting some of the assumptions about
how grounding is supposed to work in the PC.

Still puzzled,
Paul