SmartServer IoT IP-852, RNI or U60 stops working [emi? error] (KB1417)

If the SmartServer stops working on a U60 FT-10 or XF-1250 channel then it is possible that this channel may be noisy.

Sometimes a noisy USB channel may only cause interruptions in communication on the FT/XF/PL channel and not always that the U60/U70 will stop working.  Adding Ferrite bead to the USB 2.0 or for a U60 an external filter will improve communication on the FT/XF/PL channel. 

You can determine if a U60 has been detected by going to the SmartServer LON Configuration page or type "ifconfig" in a console or ssh.  For "ifconfig" you should see something like the following for each U60s (shold see "lonX:" where X is a number represent the lon channel number).

lon0: flags=67<UP,BROADCAST,RUNNING> mtu 1280
inet netmask broadcast
unspec 00-D0-71-12-E7-F0-30-30-00-00-00-00-00-00-00-00 txqueuelen 10 (UNSPEC)


Check for error messages like "disabled by hub (EMI?)" as shown below which means excess noise

2018-08-31T05:03:24+00:00 smartserver-17q5y87 kernel: usb 1-1-port1: disabled by hub (EMI?), re-enabling...

in the following files in the /var/log directory


Sometimes you will see this message in one file or possibly in all three files.

If you see similar error messages then most likely there is excess noise on the FT-10/XF-1250 channel.


Possible Workarounds:

1. Sometimes using a different USB cable helps. Make sure the USB cable has data lines.

2. Verify that the FT-10/XF-1250 are properly terminated - improper termination may cause noise

    a. FT-10 channel

        - Free-topology - Single free-topology terminator usually located near the SmartServer

        - Bus - two FT-10 bus terminators located at the ends of the channel

   b. XF-1250 channel - Bus topology - two bus XF-1250 terminators located at the ends of the channel

3. Add  an external filter to the U60 FT/10 or XF-1250 channel. Try one of the following:

   a. Use a Ferrite Bead for USB 2.0 cables

      For example,


   b. An external Filter to the FT or XF channel as shown below.


External Filter: FT-10 and XF-1250 channels

To reduce the noise on the FT-10 or XF-1250 channel you will need to add an external filter


Shown below are the schematic connections and the parts for making a male-female CM choke assembly. The connectors specified are compatible with the U60's network connectors.  


We typically solder the SMT CM choke onto a small PCB (0.1" plated-through hole proto board works) and solder the male header to that board as well.  The wires from the female plug solder into two of the holes on the proto board.


It's good to shrink-wrap the assembly for stability, but the customer can do whatever they want as far as how to assemble it all.







Mfg. Part Number

CM1 Common Mode Choke



Female Network Connector

Metz Connect



Male Network Connector

Metz Connect




CM1 --

Female Network Plug  --

Male Network Header --




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