Hello,
We don't have any reports from other customers regarding this kind of issue. The problem you are experiencing could be related to a compatibility issue with the hard drive itself so our recommendation is testing with a different hard drive brand if possible to narrow the issue. You can also test the system out of the chassis to avoid any possible grounding.
Hi Dan, thanks for the reply.
I think it more likely to be the controller in the enclosure. It's a Welland Sun Bright sata2 with esata as per this link
http://www.welland.com.tw/html/enclosure/940.html
The controller chip is a JM20329
The hdd is a 500gb samsung, model HM500JI.
The motherboard has only ever sat on a cardboard box. It has not been put in a case as yet.
Hi Dan,
Have tried this with another usb case and hdd. Result is still the same - hang at 5A
Case controller chip is a ALi M5642
Hdd is a 2.5" ide samsung 80gb model MP0804H
Nailed it!!
It's a conflict at post between my Logitech DiNovo Edge mouse/keyboard wireless usb dongle and the usb hdd.
If I move the dongle to a internal header via a usb2 front i/o panel, the hang does not happen.
If I move the usb hdd to an internal header with the dongle in a rear port, the hang does not happen.
Here's the weird thing though, if I leave the usb dongle in a rear port and plug in both usb hdd drives to rear ports, the hang does not happen, or - if I plug in one hdd to a rear port and a usb hub to another rear port, the hang does not happen.
The only configuration that causes the hang, is when only one usb hdd is plugged in to a rear port and the Logitech wireless dongle is also plugged in to a rear port.
This hang even happens with a usb pen drive in place of the usb hdd
I have stumbled across other combinations that also hang at 5A that do not involve a usb hdd or the DiNovo k/b - mouse dongle. In fact in these combinations, a usb hdd stops the hang.
I've been using a Digitech xc5146 hard wired usb k/b, a logitech v220 wireless mouse with matching c-uay59 dongle and usb sd/mmc card reader model ac- 6000
All three must be plugged to particular rear i/o usb2 ports.
Removing any one of the items = no hang
Adding a usb hdd to another rear usb2 port = no hang
The arrangements that cause a hang are:
lan and 1394 are only included as reference to the port arrangement, nothing is connected to them.
'Hub' is the card reader
'Mouse' is the c-uay59 dongle
lan 1394 lan
hub - -
k/b mouse -
lan 1394 lan
k/b - -
hub mouse -
lan 1394 lan
k/b - -
mouse hub -
other arrangements that also hung were as per above but using the ports under the r/h lan port, e.g. as per below
lan 1394 lan
- - k/b
- hub mouse
or using the upper middle port e.g. as per below
lan 1394 lan
- hub k/b
- - mouse
Whilst I have not tested all possible combinations [I'd be there forever!!] it did seem that any other combination did not hang.
Hoping this might help Intel hunt down the culprit! 
Intel - you should offer a bounty for information that leads to the arrest of a bug, then the whole world is your RnD lab!! 
[I'm serious!!]
edit: the dongle for the DiNovo wireless keyboard/mouse is a c-uv35
