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I'm facing a low power USB port issue on my desktop PC. I have a USB 2.5" external harddrive and it does not work with any of the USB ports on the computer case except for one.

Also if I use a extension cable with that port, the HDD will not work. I measured the voltage of the USB ports and they gave me about 4.60-4.70V. I updated the BIOS to the latest version. My motherboard is an AUS M4A785TD-V Evo and my power supply is Xilence 700W.

Is there any way to increase the voltage of the USB ports?

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does the port work with other devices? – user78429 Jun 5 '11 at 15:30
bckbck, obviously, I cannot say for sure, but it probably works fine with many devices that require less power. I got the sense that the external drive he is using might be powered solely by the USB port, making power critical. A mouse will use a lot less, and probably work fine. – KCotreau Jun 5 '11 at 16:03
A)How are you measuring the voltage? B)Have you tried another PSU? Also, it is very silly that you didn't think about or didn't mention about 'B'. – barlop Jun 5 '11 at 16:32
@bckbck yes wireless mouse and keyboard, and other usb devices are working on my pc. They require less power than usb hdd. – zforx Jun 6 '11 at 14:35

3 Answers 3

I doubt you can change it on your computer. You should probably buy a powered USB hub. Google "powered usb hub" without the quotes.

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I know external powered usb hubs but I want to know why my pc does not give 5V on usb ports. – zforx Jun 5 '11 at 13:39
The specification for USB is +5 DC volts. I don't regularly (by that, I mean never have) measure the voltage on USB ports, but 4.7 seems like it may just not be working right, and the hardware is bad. I would probably call ASUS and ask them about it, and if it is a problem, as I suspect, have them RMA the board. Does the external drive have its own power source? – KCotreau Jun 5 '11 at 14:05
External drive does not have it's own power source, and it is working with my laptop which give +5V when I measure it's usb ports. – zforx Jun 6 '11 at 14:31

They make usb Y cables that use 2 usb ports to properly power the drive. It draws power from 2 usb ports. image description here

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USB low voltage can impact a hard drive. I have an Apple (Fujitsu make) drive my brother gave me. I put it in an external USB 2 enclosure and used a USB connector with a Y (double USB ends)to plug into an nGear powered USB hub and then to my computer. The drive would mount and unmount and I could never complete a clone of my internal drive. I ended up just plugging it directly into one of my Mac Mini's USB port (just using one of the USB ends) and I didn't have any further problems. This leads me to believe that hard drives are especially sensitive to power sources as the Y connector didn't seemingly provide enough juice (even double plugged in with a powered HUB). Also, my 2012 Mac Mini has USB 3.0 which I understand provides more power (in the range of 900 mA verses 500 mA for USB 2). This boost may have helped things.

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Welcome to Super User! This is really a comment and not an answer to the original question. To critique or request clarification from an author, leave a comment below their post - you can always comment on your own posts, and once you have sufficient reputation you will be able to comment on any post. – DavidPostill Oct 13 at 14:19

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