P
Paul
"Jim Gibson" said:MMmm...
Interesting stuff..
So Paul, am I to understand that if there was an incident of small static
discharge trying to ground itself through the outer wall of the USB
connector - through the ground wire and then to pin 10 of the board header -
all would be well?
If pin 10 is NC and it receives a micro jolt or a few milliamps wouldn't
that be enough to cause damage?
JG
The only solid evidence we have right now, is the Gigabyte
web page. The advice I've given above is basically repeating
what Gigabyte is saying, only I consider the problem to be
more severe than they do. I don't feel that any grounding
scheme is sufficient to protect the motherboard (based on
reports that plugging into the motherboard USB connector
stack on the back of the computer is also killing boards).
http://tw.giga-byte.com/Motherboard/Support/FAQ/FAQ_456.htm
"The ICH4/5 SouthBridge chipset on my Intel motherboard
appears damaged or "burnt". How did this happen?
The GIGABYTE Global RMA Service Center has recently become aware
of the randomly occurring risk to ICH4/5 SouthBridge chipsets on
Intel motherboards to become damaged or "burnt" when a USB device
is connected. Please read the following paragraphs to learn more
about this issue.
Why did this happen?
There are three likely causes:
Accumulated static electricity from the human body may have been
transmitted to the ICH4/5 SouthBridge chipset when connecting a
USB device if it has not been "grounded". A connected USB device
does not have any static electricity protection. Accumulated
static electricity in a front-panel USB port that is not properly
"grounded" with the PC casing.
Usage Tips
- Avoid touching the USB connector.
- Release static electricity within your USB device by touching
the USB connector to any metal surface before plugging it into
your computer.
- Use rear-panel USB ports on your PC whenever possible.
- Use a three-pronged electrical cord to connect a power supply
to your PC.
- Use only approved or certified power supplies."
The Asus 2x5 connector uses only eight pins. There are two ground
pins. A typical USB installation needs three ground signals.
Two grounds for the ground pins in the two USB connectors. Plus
a shield connection is needed for the outside of the USB connector.
A good cable assembly will take one of the USB signal grounds
and splice the shield wire into it too (good here meaning not
good design practice, because that is not good electrical
design practice, but good as in working within the compromises
that Asus has created by not having a third ground pin).
VCC
D+
D-
GND -------------------------> To one Asus GND pin
VCC
D+
D-
GND ------------+------------> To the other Asus GND pin
|
GND_shield -----+
If the GND_shield is connected to NC, and static were to be applied
to the wire, the question would be, how much static voltage, and
how much clearance is there from the unconnected pin to any adjacent
conductors. The USB data signals might not really get very close
to that pin, so whether this is an issue or not really depends on
the layout of the board.
Since we don't know how sensitive the USB ports really are,
it could be that just dumping static discharge into the metal
of the computer case is enough to cause latchup in a USB port.
I cannot discount that as a possibility, but there is no way
to protect against that. The advice I've given assumes the
motherboard is resilient enough not to be affected by a static
discharge to the chassis, but only time will tell whether this
is true or not (we know Asus or Intel won't be telling us). I'm
hoping that by removing any "antennas" from the USB headers, and
keeping away from the rear motherboard USB ports, that most users
will enjoy use of their motherboard after the warranty has expired.
Paul