A few days ago a friend told me he had a nasty crash. An externally-powered USB hub screwed up his motherboard on the laptop just after he plugged in the power brick. He even showed me that hub. A 10-port hub just like the one I got from china (DX or aliexpress – I do not recall). The only difference – he picked up his at a local shop for twice its actual price. So, once I got to my lab, I cracked mine open to have a look what the heck could deal such a damage.
Inside it’s a 7-port Fe2.1s hub with an Fe1.1s hub (4-ports) wired to one of the ports giving 10 ports in total. The usb jacks are soldered really poorly and would eventually fall apart after some time, so I fixed that. And next, it looks like I have found the possible cause.
So, we have 2 sources of power. USB and DC Jack. We should pick one to use. Instead of using a dedicated power MUX, they hooked up a diode (judging by the silkscreen). But later (either to cut the costs or to get rid of the losses on the diode, they soldered in a 0 Ohm resistor, shorting the power lines.
As a result, if the voltage of the DC supply is higher than USB, we get a reverse current. And if we pick a wrong supply (overvoltage, or reverse polarity) – this can deal some pretty serious damage… The simplest way of solving this – was to get rid of that crappy 0 Ohm short, and hook 5 volts from a dedicated power supply, build around an old soviet transformer dating back to 1972, since that baby can handle some serious load of some 5 to 8 amps at 5 volts.
Thanks for this! I just got a similar 7-port hub off eBay and it doesn’t even have the pretense of a pad for a protection device; 5V from USB is connected directly to the power jack with a nice thick trace. Also draws 100mA with *nothing* plugged into it, apparently within the specs of the chip.
I got the same hub from ebay, i always tear my things down and check them for defects on the board. when I open the hub I found out that there is no caps on the board, bad solder joints. and the same thing that you found, not using a diode. the diode is there to prevent power from the power pack going back into the computers usb power. and if its a cheap power supply , you can test this or just toss it in the trash and get a new one / build your own. just to show you that paying for cheap things can cause horrible problems.
I got one of these hubs from Staples about 6 months ago, luckily my motherboard shut off the USB BUS it was on before it could do any damage. It’s gone from Staples site now, I was going to leave a review about it but the page was gone.
I ripped it apart and found what you found with the diode on the silkscreen, but one other thing I found is that the power adaptor that came with it is rated for 1000mA, when according to what I understand about USB standards, one USB device can draw up to 500mA, and the FE1.1s needs about 100mA to run at full speed. So it should have been a 5.3A wall wart, not a 1000mA one.
Also if you open the wall adaptor up (CAUTION! The capacitors could have high voltages in them) , you’ll find something strange, it looks like the board inside was originally made for a 1 port USB charger, not a USB hub. The VCC and GNC wires in the cord are just soldered to the holes for the VCC and GND on the USB port footprint.