USB (or power supply) fault

  scotty 12:24 12 May 2003

I use an optical mouse attached to a USB port. The mouse has stopped working (the light does not come on). I connected the mouse to another PC and it works. I connected a gamepad to the USB port and it was not recognised by the system. However, my scanner does work when connected to this port. The only possible reason I can see for the scanner working is that it has its own power supply while the other devices obtain power from the USB port.

Can anyone suggest how to tell what has failed?

sounds to me as if your detective skills are top notch.if the port in question is directly attached to the motherboard theres not a lot you can do about it but if its attached to a pin header with a lead to a bridge on the back or front of the case check the wires are all ok.
is there any problems showing up in the device manager?

  scotty 13:18 12 May 2003


Connectors go directly to the board.

Device manager shows USB ports working correctly.

If it is a power supply that has failed, do you know if this is obtained from the main pc power supply or is it generated on the board?

wheyou say the connector go directly to the board
do you mean there is a lead coming off a pin header( metal pins sticking out of the board) or are the ports built in at the top left at the back of the case under the psu? well either way theres not much you can do about it , the power is delivered on a line on the motherboard which you cannot repair, if the port is on a bridge from a pin header you could try replacing it bcause the problem might be in the wires there,

isuspect you probably have more than one usb port
so the easiest thing to do would be to buy a 4 port hub (preferably self powered) and plug your devices into that.

  scotty 14:52 12 May 2003

USB connectors come directly from the board. Unfortunately, both USB ports have the same symptoms. There are also connectors (pins) on the board which are not used (but I may have to resort to these).

The manual for the board talks of a POLY FUSE which protects the pc from dangerous voltages input at a USB port. This is a self resetting fuse. Perhaps this fuse was activated. I will check tonight if to see if this reset.

  scotty 08:51 14 May 2003

Checked out USB ports again. They work (including supplying power) to a game pad. In Device Manager, current to port is given as 100mA. Adding another device (mouse) is sufficient to pull down the power supply and stop all USB devices working.

Have also noticed that lights on network card are not lit. So this points to a power supply problem. Network card presumable gets its power through the PCI connector. How can I tell if it is a fault on the motherboard or with the power supply? Is the only way to try replacing the power supply?

  scotty 11:26 15 May 2003

Tried replacing power supply but problem still exists. Stripped all unnecessary cards from pc and tested - USB still not working. Rebuilt pc with all original parts - network working again but USB still falls over when mouse connected.

I take this to mean that a fault has developed somewhere on the motherboard which affects the power supply to the USB ports. Do I have any alternative other than to replace the mobo? If I fitted a powered USB hub would this overcome the problem?

Any suggestions welcomed.

From what you have said, it is probably worth buying a powered hub, if it doesnt work, you can always get a refund!! ebuyer have got a 4 way hub & psu for £7.99. At least it will allow for any further expansion. click here

This thread is now locked and can not be replied to.

Elsewhere on IDG sites

Fujitsu Lifebook P727 laptop review

Best of the Grad Shows 2017: University of the West of England (UWE)

Best value Mac: Which is the best £1249 Mac to buy

Les meilleures GoPro 2017