Ethernet stops working after connecting USB-serial device

bftrock · Post by **bftrock** » 25 May 2018, 18:43

For some reason I can no longer communicate with my RevPi Core 3 after connecting a USB-serial converter device and rebooting. I can't connect with SSH, nor with WinSCP, and it doesn't respond to ping. I'm using a DHCP reservation so I'm certain of the IP address. Is there any hardware reason for this? I see that you sell such devices in the Accessories section of your Shop, so I assume this is something you've designed for. Apologies if this is already answered in the Forums, but I couldn't find any relevant articles.

Thanks,
Brendan

volker · Post by **volker** » 26 May 2018, 12:30

Hi Brendan,
is the Core alive? Can you see it booting when using an HDMI monitor? If you have connected any other module to the PiVridge doe the red lights change into green after boot time?
If not you might have suffered from a backward current which might occur under certain circumstances and which can destroy the power input protection parts of the core:

Connecting a lab power supply which does have a potential difference between GND and earth
Not connecting the RevPi Core FE terminal to earth
Connecting a switch which does connect the RJ45 / CAT5 shield to earth
Using a USB device which shortens the USB GND with USB shield.

Depending on the potential difference the power supply builds up against earth this constellation is able to destroy the power input section of RevPi Core. This is why we urge the users to connect FE under all cricumstances (it is mandatory for a protection of the device). There is a problem to design an input protection circuit which can withstand industrial grade surge and burst signals while at the same time allowing consumer grade IOs like USB which in many cases does confront you with non compliant devices on the market (connecting Shield and GND in a USB device is non compliant to USB norms). The way we solved these problems where to insert a separate path for destructive energies over an FE terminal ("functional earth"). But if this terminal is left open you take a certain risk to get the destructive energies rooted over poor protected circuit pathways.
If your Core has suffered from these circumstances and is no longer alive please return it to KUNBUS and we will replace it. And please always use the FE terminal and never leave it open (connect it to the DIN rail which is normally connected to PE, or at least connect it to GND).

bftrock · Post by **bftrock** » 08 Jun 2018, 19:31

Thank you for your reply. I'm not sure why, but this issue seemed to resolve itself. So it looks like there was no hardware damage.

RMeissnerCC · Post by **RMeissnerCC** » 02 Jun 2020, 14:56

Dear Volker,
this is an interesting post. Is there any way of knowing whether the power input section is broken? Our device is working properly, but probably did run without proper FE connection for some time.
Best, Robert