Questions about GIGABYTE products > Motherboards with AMD processors

USB static discharge causes instant reboot on GA-MA785G-UD3H

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scottlindner:
I did consider a 5.25" front mounted media reader that includes USB ports and just skip the case front USB ports.  They are really handy so I'm going to give this a shot, but if this replacement from Antec doesn't work I'm going to get a good media readier with USB ports just as you suggested.  Part of this is solving the problem now, and not just getting a workable solution.  I'm sure you're familiar with that, just gotta figure it out for the sake of figuring it out.

I'll be sure to leave everyone know what's going on.  I also plan on posting how this works out on the NewEgg reviews since about five people have posted the same issue.

Scott

Pottypete:
Hi,
Just dug up some old info,
Looks like you have to check your pin out connector with the mobo pinout in the manual,
I know there old posts BUT,

The USB port consists of:

1) Connector shield. That is the metal body of the USB connector.
It makes contact first. The shield on the computer side _MUST_
be connected to ground. When an appliance is "hot plugged",
static electricity on the USB cable is transferred to ground
when the shields of the two devices touching first.

2) Take a look at the pins inside the USB connector. The outside
pins are longer than the inside pins. The outside pins are
+5V and GND. They make contact before the two shorter data
pins. By having the power pins connect first, that prevent
currents from flowing through the data pins without a logic
ground in place.

Everyone should check their USB front port wiring. Make sure
that the shield around the four pins, is at ground potential
with respect to the motherboard. This is complicated by the
fact that the motherboard header only has enough ground pins
for the signal pins.

/ USB+5V (VCC) X X (VCC) USB+5V ----> \
To __/ USB_P5- (D-) X X (D-) USB_P6- ----> \__ To
USB \ USB_P5+ (D+) X X (D+) USB_P6+ ----> / USB
pins \ GND (GND) X X (GND) GND ----> / pins
/ X NC \
_____/ \______ GND must also
GND must also go go to connector
to connector shield metal!
shield metal!

Check the design of the front USB adapter plate, and make
sure that the connector shield is grounded. Using an ohmmeter,
you should measure zero ohms between the shield of the USB
connector and the bare metal of the computer case (as the case
is grounded via the PSU case and via the brass standoffs that
contact the ground rings on the bottom of the motherboard).

If the connector shield is well grounded, perhaps future
"hot plugged" USB devices will not destroy any more motherboards!

Or, simply stop using front mounted USB. Only use the USB ports
on the back of the computer, as the ground is established by
the motherboard design. If you don't own a multimeter, or
don't wish to fiddle with wiring, just stop using the front
mounted ports. You can always bring a USB cable from the
back of the computer, up to your desk.

Regards

scottlindner:
I just received and tried the replacement USB module Antec provided.  I'm having the same problem.  I seriously am wondering if the mobo is somehow involved with this problem considering all of the tests I have tried.

I'm going to try a front mounted media reader with USB ports and see how that goes.  If it works, I'll just disconnect the front ports on the case.

Scott

troy216:
I am having a similar problem with the same motherboard but a different case.  My case is the APEVIA X-MASTER HTPC.  I get the reboot whenever i zap the front part of the case.  The closer to the on/off button I touch, the less of a zap is needed.  In fact, I can touch the on/off button and not even perceive a zap and it will reboot.  I suspect that the ESD is making its way into the power on/off or reset wires and into the motherboard's header pins.  So it may not be your USB ports, just that they are close to the switches that connect to these headers.

Did you follow the recommendation of the earlier poster to disconnect these headers?  I will try myself to see if it resolves my issue.

Pottypete:
Hi,
More info from the web

http://tw2005.giga-byte.com/Motherboard/Support/FAQ/FAQ_456.htm

It seems that some (older) cases (and I am not sure it is all Antec here) have an extra ground wire for the 9th pin on the USB header. Now if you read the Asus mobo pinout it says N/C for that pin. So by having this wire hooked up to the 9th pin I am assuming that is is dumping some static electic into the circuit and that is what might be starting off the burning up process. I also assume Static Electric that is setting it off b/c it does not happen all he time. So I call Antect to confirm my theory and I was told that in other words, most mobos/systems would shut down if you had the 9th wire (ground) hooked up. However it causes the S bridge to fail. Antec says this wire is not to be hooked up if the pin out says N/C (no connection) or O/C (open connection). Now some of my new cases that i have recently built with Coolermaster and my own personal Antec P160W does not een have a 9th wire. So it seems that they are dropping this ground out. I wonder why....
Have a look at this:


It seems the ICH5/ICH5R are sensitive to static discharge. If
the static enters a USB port (the USB port is hosted by the
Southbridge ICH5), it causes an electrical phenomenon called
"latchup". Latchup is where a phantom PNPN semiconductor junction
forms - that is the same structure as an SCR. Latchup turns on
the junction, and the junction sits across the power rails of
the chip. A _large_ current flows through the ICH5 and it gets
really hot - so hot in fact, that it can burn. The Southbridge
can be destroyed in a matter of seconds.

One solution,
Just reporting that the solution of grounding the MB by removing the red insulator on one of the screws securing the motherboard to the case has seemed to fix the reboot problem when I touch the USB port.

I am guessing that my MB was not able to dissipate the static discharged because it was not properly grounded. I pretty much use the insulators on all builds, but I think in this case, the head on the screws I used this time were small enough that they never made contact to the MB when I used the insulators.
solution 2,.
Ok, so you don't know how long I have been scouring the internet to try and find a solution to the one single flaw of this case: The fact that the front panel isn't grounded. I would walk around, build up static and then touch the front of my computer and everything would just go blank. It wouldn't restart, wouldn't respond, but it would still be on - like the fans and everything would still be running but just a blank screen. I finally read in these reviews about people having a similar problem and how they manually grounded it. I took a piece of speaker wire and wrapped it around a screw that went into the front panel then grounded it with the psu and ta da! No more random shut downs.

solution 3,. FROM ANTEC CS
UPDATE!!!!

Called Antec customer support. They said they are aware of the problem and have no fix for it. They actually told me that the only thing that seems to work at this point is to tape a wire to the front bezel and connect it to a screw in the back of the case. Also said they are working on a harware fix and will send it once once is found.

The problem seems to effect HPMC cases as well

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