USB hub fails with some devices

Posted on 2009-07-02
Last Modified: 2012-05-07
I am an independent tech. This is for my customer. I need an answer BEFORE I go onsite so there is no more info to provide you other than what is below.

USB devices work when connected to the 5 usb slots on the 64 bit OS and 64 bit HW Vista PC (a Sony VGC-JS100) that looks essentially like the flat panel iMacs that have been sold for the last few years). However, my customer has more than 5 usb devices so she bought a GE brand usb hub. When she connects more usb devices to the USB hub some problems occur; my customer was not specific. BUT IT IS NOT THAT THE USB HUB DOES NOT WORK AT ALL.
If devices are NOT connected to the USB hub, there are NO problems.

USB devices attached are keyboard, mouse, iPod, Printer, USB stick (also called flash drive I believe). Additonal USB devices are an external HD and more USB sticks. The brand for some or all of the usb sticks is ScanDisk.  I do not know which are attached to the USB Hub and which to the PC and this may vary from time to time.

Also note that with the USB hub attached there are only 4 available USB interfaces on the PC so all USB sticks and the external HD go into the HUB (as the keyboard, mouse, iPod cable, and printer are probably permanenty attacvhed to the PC and then also the USB hub.


(1) MY OWN VERY LIKELY SOLUTION: Replace the GE Usb Hub with a SELF POWERED USB HUB because the PC does not supply enough power for all these usb devices (especially the external HD). A Self Powered USB hub is one with an attached AC adapter.

(2) MAIN REASON I AM POSTING HERE: Another solution has occured to me: The PC (either the Vista OS or the PC HW itself) does NOT support an unlimited number of USB devices and when the maximum allowed is reached, no additional USB devices will work OR one of the currently attached USB devices will fail REGARDLESS of whether they are attached to a USB hub or not.

(3) Some other solution you will provide me with.


Question by:mgross333
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Accepted Solution

Pete_Zed earned 300 total points
ID: 24767432
I would personally go with the powered hub (Solution 1). That's a lot of USB devices to run off a USB port so I think the PC may be struggling to provide enough grunt to keep all the devices working correctly and up to speed.
LVL 49

Expert Comment

ID: 24767462
No 1 is what I would do.  It is quite possible you may need two powered USB hubs.

You can connect up to 127 devices to a USB controller so the number of USB connections shouldn't be a problem.
LVL 19

Expert Comment

by:Rob Hutchinson
ID: 24767478
Yeah #1, or without getting another USB hub, just make sure at least the printer is plugged directly into the computer not using the hub.
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Expert Comment

ID: 24767564
Number 1, no doubt.

Author Comment

ID: 24767805
Thanks, that is enough replies. I will award points after tomorrow when I will be onsite and replce the current USB Hub withl a powered USB hub.

LVL 92

Assisted Solution

nobus earned 100 total points
ID: 24770433
there are max 127 USB cevices possible :
so, i agree with #1 solution - why ?
because each usb output is MAX 0.5 A x 5 V = 2.5 Watts
it is easyly overloaded; and can burn out the usb chip, - so i suggest ALWAYS to use a POWERED usb hub !

Author Comment

ID: 24771627


>it is easyly overloaded; and can burn out the usb chip

(1) If her usb mouse and keyboard and printer are still working CAN WE ASSUME THAT THE USB CHIP IS NOT BURNT OUT. Also is there ONE usb chip for the entrie PC or just for each USB interface ?

(2) My customer mentioned yesterday that all the data on her ScanDisk USB stick was missing (she may have had it AT THE TIME plugged into the PC rather than the usb stick; I am not sure. Could this have been caused by plugging it into the USB hub given what is above. I just assumed the problem was additional devices would not be recognized on the USB HUB, NOT DATA DELETION.

(3) Regarding
> because each usb output is MAX 0.5 A x 5 V = 2.5 Watts
Are you saying that an external 500 GB Hard Drive uses 2.5 W but a mouse or kjeyboard use LESS THAN 2.5 watts (i.e it depends on the device) AND ALSO what is the total wattage available for all USB devices WITHOUT a self-powered (AC adpater type) USB hub?

LVL 49

Assisted Solution

dbrunton earned 100 total points
ID: 24772323
(1) Depends on implementation on motherboard.  Common implementations used to be one chip per two interfaces.  You can probably assume if it works that the USB chip isn't burnt out.

(2) Could be a number of reasons there.

(3) Each USB port can supply 2.5 watts (in theory).  An external hard drive may draw less than or more than 2.5 watts.  Some external hard drives come with 2 USB connectors to ensure they get sufficient power.  This is because either some computers don't supply enough power or the hard drive is demanding more than 2.5 watts.

Keyboards and mice are not power hungry devices and as you say it depends on the device.

Total wattage = no. of ports x 2.5 watts.  (in theory)  Again note that some computers may not supply this power.
LVL 92

Expert Comment

ID: 24773404
1- if something usb does work; it's ok for me -  btw i never said it was burned out, only that you CAN burn it out easily

But the point is : if you keep adding device s together on ahub, you can bet your mother in law you're running into problems ! if not for overloading the power -  you are sharing 1 ports bandwith      !      
2- keep in ming those things die frequently; if you want to try to revive it, say so.
3-all devices will add the power they use, when connected to the same usb port via a not-powered hub

that's why i ALWAYS recommend powered USB hubs -  you never know what they're gonna stick into next... (héhé)

Author Closing Comment

ID: 31599356
300 to Pete Zed for being the first one to post the correct answer. 100 points to the other two Experts for providing an additional level of detail


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