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rickman

wrote on 12/30/2017 12:02 AM:
I have one of these USB hubs with several USB connectors, which plugs
into a single USB port on a computer. It dont work. If I plug in a flash
drive directly to the computer, I can access that drive. But if I plug
it into the hub, the drive never shows up. I tried this on 3 computers.

I opened that hub, and there is a circuit board, with each output port
connected to a trace on the board which goes to a black dot on the
board. I dont know what that "dot" is, but I assume it's a chip of some
sort, and it looks like the dot itself was some sort of epoxy placed in
the board.

This was a gift, and it's going to get returned to the store, but I am
just wondering what kind of circuit this is?

Until looking at the innards, I thought that these hubs were just a
direct connection to the input (from computer) USB. But I see there is
more to it....

USB is a point to point interface unlike some versions of Ethernet (using
coax) or an RS-485 multipoint interface. To connect more than one device to
a USB port requires a hub. The hub has a chip which receives packets sent
from the computer as well as packets received from any of the down stream
ports, buffers them and retransmits them on the appropriate other port.
That multiport interface chip is what is under the blob of epoxy on your
board. They use a chip directly with no package because it saves a few
pennies.

When you plug the hub into your computer it should show up as a hub. Under
windows you can go into the device manager and find it there. If the driver
did not install correctly it will show with a yellow error symbol next to it
and be listed as an unidentified device. If it doesn't show in the device
manager list at all while the flash drive works in the PC port, the hub is
defective. If it shows up but with the driver error, you may need to search
the Internet to find a driver.

--

Rick C

Viewed the eclipse at Wintercrest Farms,
on the centerline of totality since 1998