Sunday, May 26, 2013

Backfeed / problem USB Hub(s) on the RPi!

New Plugable high speed 7 port USB Hub

The first USB 7 port hub had major problems right from the start.  Even though it had a 2 amp power supply and was a package deal item on Amazon along with the Raspberry Pi.  It was a no name hub that would cause the keyboard to miss or repeat keys really bad.   So much so,  that I bought several keyboards while trying to find the problem.  Finally it burned out the USB connection to the Raspberry...  Not on the RPi itself .  The one on the hub.
 So the next one, I went with a name brand and made sure it was on the list of verified working devices for the RPi.  It was the Belkin F4U040 4 port hub.  I used it for a couple weeks before I  started having keyboard problems again.  I found that I could fix it by powering up the RPi first and then powering up the hub.  I also found that it was backfeeding the Raspberry Pi.   If I unplugged the RPi with the hub still plugged in,  the Raspberry Pi stayed turned on!   Not a good situation and could have really damaged the little computer!   I notice now they have it listed under the approved USB hubs, but with a note that it backfeeds.  Then it is listed TWICE under 'problem'  devices!  But it is still 'verified'!
 Well, I have been running my 3rd USB hub for a few days now...  No sign of a power
problem and I have checked it a few times/ways and there is no sign of a power backfeed problem at all.   So this one looks like it is a good choice and 100 percent compatible with the RPI (and the blue lights look cool as well!).  It is the Plugable High Speed 7 port USB 2.0 hub with a 3amp power supply item #USB2-HUB-AG7. Supplies 500Ma to 6 devices and then 428Ma to each when the 7th item is added.  Way better than any of the others I have researched.   Could even power the Pi off 1 port itself (makes my head hurt thinking of the problems that could cause in time and space... Don't do it.. Grin). This is a free plug to them from a happy customer!  Finally!
  I can tell you,  the wrong hub or too much power drawn straight from the RPi causes all types of weird hardware failures and even makes the Pi act weird itself. Things you will blame on everything else in the system.  Why not would a 2amp hub with only a keyboard and mouse cause the Pi not to load the ethernet network and reboot it?  It can!  Weird stuff?  Check the hub!  Check for backfeed.  Unplug the Pi, leaving your hub powered... If the rpi stays on.. Definitely have a backfeed problem.. Check the voltage on the board under these conditions with a voltage meter.. You may have less of a backfeed problem.  The usb hub should not send power 'back'  to the computer through the cable that is sending the data. If you think you have a hub power problem.  Remove the hub.  Even for a short test period and see if your problems persist.  If you need a new hub,  make sure it is verified to work with the rpi and check with actual users to make sure they are happy with it!
Macally that caused so many probs and burned out!