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This may be similar to USB hub damages an external hard disk (and storage devices) on use attempt.

My question is at the end of this description. I purchased a cheap PORTS brand USB 2.0 hub to use with my HP ProBook 4430s running Windows 7 and discovered that it quickly damages connected devices. First I connected a 10 meter repeater which is in turn connected to a WIFI adapter. Immediately it started going not available intermittently.

At the time I thought there might be a power limit and removed it. Then I connected a USB to SDHC adapter and quickly found the SD subdirectory and some files to be corrupted. Same for a second USB to SDHC adapter. After further testing I have found that the SDHCs are undamaged but the adapters are damaged. They seem to draw about twice the normal power and produce many errors when reading or writing the SDHC when directly plugged into the computer and sometimes become not seen. The WIFI system continues to become not seen intermittently while connected to the computer port. Everything was working fine before I used this hub.

Opening the hub, the power and ground to straight through to all ports so it is not a power problem I connected a scope to the hub’s power bus and could not see a problem. My guess is that somehow these devices were damaged and are intermittently rebooting.

My question is there a way the hub could send errant signals of the correct voltage over the data lines that would result in damage? (for example telling a connected device to send data but continue to send data resulting in overloading the bus transceiver which may be on the same chip as other logic)

Sathyajith Bhat
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robeyw
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  • I can't judge whether this is the case, but if you have a question that is advanced electrically, then it can go on electronics.stackexchange.com but hennes looks like he knows what he's talking about so maybe you have your answer here, but if so then you got lucky 'cos most here aren't electronics gurus – barlop Aug 13 '15 at 09:15
  • @barlop It would probably get closed as off-topic, since it's essentially a use/repair question, not a design one. – Dmitry Grigoryev Oct 21 '16 at 12:28

3 Answers3

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Opening the hub, the power and ground to straight through to all ports so it is not a power problem

Uhm, it is not. I thought that this is a recipe for problems.

USB2:
Minimum power available per port: 1 bin, aka 100mAmp.
Maximum power available per port: 5 bin, aka 500mAmp. The device should only draw this much after asking and after getting a reply which states that it is ok. (It can be denied if the source does not have sufficient power reserves).

Now for an unpowered hub:


Computer (max 5 bins)   ---------------  [     3 port   USB HUB        ]
                                            |          |         |
                                            |          |         |
                                            D1         D2       D3

Since We can connect up to 3 devices we either have logic to allow D1 to draw up to max power and shut down D2 and D3 (else we can go over power budget), or we need smart logic so that D1 never draws more than 3 bins.

Neither of these make sense with directly connected power lines.

This alone is reason enough that I would not use such an hub. Instead use a powered USB hub with onboard logic.


Now to your quesion:

is there a way the hub could send errant signals of the correct voltage

I doubt this. But I an see how voltage would drop too low. And that might cause at least some problems.

Hennes
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  • I know the power does not drop low but when I get a chance I will check the logic levels. Possibly they are 5v rather than 3.6v – robeyw Aug 14 '15 at 09:28
  • "This alone is reason enough that I would not use such an hub" - You may be using one without knowing. Lots of USB hubs skip proper protection, yet everyone uses those with no problems. E.g. Raspberry Pi dropped power logic since revision 2.0, because it was doing more harm than good. – Dmitry Grigoryev Oct 21 '16 at 12:26
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I did some checking at low speed and high speed with a 200 MHz scope and all voltages were reasonable but 200 MHz is not enough to fully evaluate high speed signals. I also ordered more of the dammaged USB to flash storage adapter and it eventually failed so I am inclined to believe that the failure was coincidental but the signals are probably marginal in timeing or amplitude which accounts for the unreliability with all hagh speed devices.

robeyw
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There are many ways in which a hub may damage USB devices. It may be driving D+ and D- lines too high (those are limited to 3.6V). It may create short voltage spikes on any lines, which you didn't see with your scope. It may sink too much current when the USB device is transmitting.

The cost of equipment and effort required to nail down the actual problem will probably be several hundred times the cost of a new hub. So just buy a new one (and a new SD reader and WIFI adapter now that yours are damaged), and avoid cheap dodgy stuff in the future.

Not having any protection in power circuits is a common corner being cut in cheap USB devices. This should have no effect as long as devices you plug into the hub respect their power limits, i.e. never draw more than 500 mA.

Dmitry Grigoryev
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