onboard USB power issue?

I have an external laptop HD in one of those neat USB cases. MB is a
Gigabyte 8IRXP.

When connected to the USB2 ports on the rear panel the device correctly
powers up via the USB port VCC.

When connected to an added USB port via the mainboard jack it works but only
if I provide external power. Wiring to mainboard USB jack is correct -
checked, rechecked and re-rechecked.

Anyone else seen this problem or - better yet, have a solution?

In message , RoyB
writes
>I have an external laptop HD in one of those neat USB cases. MB is a
>Gigabyte 8IRXP.
>
>When connected to the USB2 ports on the rear panel the device correctly
>powers up via the USB port VCC.
>
>When connected to an added USB port via the mainboard jack it works but only
>if I provide external power. Wiring to mainboard USB jack is correct -
>checked, rechecked and re-rechecked.
>
>Anyone else seen this problem or - better yet, have a solution?
>
>
>
Not specifically on that board, but I have very similar problems with an
add in USB board and a secondary (powered) hub.

Plug a hard drive into the add in board rear ports - works fine, plug in
to an external powered hub - fails!!

My diagnosis is that the "over current" protection for the USB port in
the external hub has a lower setting (tolerance around 500ma nominal?)
than the add-in USB Board, and that the external hard drive (rated at
500ma) just exceeds it.

I can only suggest

a) External power
b) A different added USB port unit ( the tolerances may be different)

A word of warning. I had an external drive "fail" under these conditions
that needed me to install the failed external drive as an internal and
perform low level formatting to recover it.

--
Peter R Cook