Re: USB problem
- From: Paul <nospam@xxxxxxxxxx>
- Date: Sat, 04 Jul 2009 18:39:13 -0400
Neil wrote:
I started this post in may and did have some positive feedback, thanks for the replies.
Unfortunately I have only ust had chance to report on the current situation.
This is my original postI have a PC running Windows XP home. I have both front & rear USB ports.
If I plug a printer into any of the USB ports, the PC shuts down with out warning.
If I plug a USB memory stick into any of the ports, the same thing happens.
I have a USB extension lead, if I plug the extension lead into any USB port and then plug the memory stick into the extension it works OK.
I have recently installed a PCI USB card, the computer still shuts down when devices are plugged in.
Any suggestions?
So a PCI card has been used to see if the problem was with the onboard USB controller which made no difference, also the PSU has been replaced which also made no difference.
Does this now look like a motherboard fault?
Thanks
Does the PCI card also operate the USB ports from +5VSB ?
Power off the computer. Plug an optical mouse with a glowing red LED for lighting,
into the PCI card. Power on the computer using the switch on the back. Boot
the computer, and verify the mouse lights up. Now put the computer in standby.
Does the mouse remain lit ? Then the card is using +5VSB for USB powering.
The theory I had before, is that the inrush transient from the connected
USB device, is causing the shutdown. Normally, a USB port has an electrolytic
capacitor near the header, which smooths out the transient.
In this photo, notice the four black cylinders, near the four USB headers ?
They protect against voltage droop caused by the plugin of USB devices.
http://c1.neweggimages.com/NeweggImage/productimage/15-158-045-02.jpg
Those capacitors are there, to reduce the loading effect caused by the
initial plugin of a USB device. They would help prevent the "rail"
from being flattened by the startup transient. Figure 1b in this
document, shows what happens to the power rail, when a USB device
is plugged in. This is caused by the charging of any capacitors
inside the USB device, rather than the silicon chip inside the
USB device drawing the power. That is why it is called an "inrush"
current.
http://www.usb.org/developers/whitepapers/power_delivery_motherboards.pdf
That is my suspicion as to the mechanism. The droop is so bad, the
voltage drops to zero for a very short period of time.
One cure for it, is if the PCI USB card had a three pin header, which
offered to run the USB ports from the hefty +5V rail, instead of the
wimpy +5VSB rail. If the +5VSB rail is flattened, one side effect,
is the motherboard is no longer able to hold PS_ON# in the ON state,
and the computer shuts off. In a quick search, I'm not seeing a
three pin header on add-in PCI USB cards.
While I suppose it could be the power supply itself, choosing to
shut down and latch off, you've already checked for that by changing
the power supply.
This USB card, has provision for extra power flow, via a floppy disk
connector on the surface of the card. What this suggests to me, is the
card is powered from +5V, rather than +5VSB.
(Manuals, mentioning the floppy power connector)
http://www.siig.com/Manuals.aspx?pn=JU-P50212-S5
Siig charges more for their products, for no particularly
good reason. They like to cover up the chip numbers, with their
product sticker. But this is the first card I can see, with provision
for external power input. (It is not the power connector itself which
impresses me - the connector implies operation is via +5V, as they
could not mix +5VSB with +5V operation quite as freely. So the fact
the power connector is there, suggests they *may* be using +5V, which
would be more resilient.)
http://www.newegg.com/Product/Product.aspx?Item=N82E16815150097
You don't need to connect anything to the floppy power connector for
the first trials. If the card works without it, and the computer
does not shut down when something is plugged in to the PCI card,
your job is done. If the computer shuts down, then connect a floppy power
cable from the power supply, to the card.
Each USB port on that card has an electrolytic capacitor in place, so
the card does have some provision for Vdroop.
You can buy power leads, to do conversion from one format to another.
For example, this lead converts from Molex four pin (LP4) in the
center of the picture, to both a SATA power connector (on the left)
and a floppy connector (on the right). You'd use one of these, if
there were no spare floppy connectors.
http://www.startech.com/Share/Gallery/Large/LP4SATAFMD.Alarge.jpg
This one is a bit simpler, converting a Molex to a floppy connector.
http://www.xpcgear.com/floppy4pin.html
And a "Y" cable, can be used to create a spare Molex.
http://www.newegg.com/Product/Product.aspx?Item=N82E16812198025
HTH,
Paul
.
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