I will check the resistance. For sure the Link LED does not stay on.
How do I check the components of the FXTI? What is the item called with the name Yuanxin on it? It has a green and a red LED light. Do the PCB boards fail?
I am just trying to nail down which component might need replacing?
From reading the forums some boards are defective and have bandwidth issues.
Maybe getting a replacement board is needed?
Update: Interesting when I plug the short RJ45 jack coming from the black item with the name Yuanxin on it (what is this device called and who makes it?) and I give it USB power, the Ethernet connection comes alive in my computer adapter and the Red X disappears. So something is not right with the other components of this FXTI, namely the Interface Rev2 circuit board. We need detailed explanations from BR. How robust is the black item with the name Yuanxin on it? More Chinese junk? Replace with something different? Suggestions?
Update: Got an email from Support and they didn’t mention any problems with the Rev2 Interface board. Warranty only 90 days! Way too short for a board like this. But is this the problem? I am looking for an alternative to this unreliable hardware. The info on BR website says the hardware/software are “open source” but don’t say anything about this Yuanxin item attached to the mounting board. But just now found the website…X-3501 YUANXIN USB3.0 to 1000Mbps RJ45-深圳市源欣实业有限公司.
Looks like the FX system comes with a model X-3501 but a better quality one is the X-3519, so if I change the BR X-3501 stock one to the more robust X-3519 one will I get a better performance?
I decided to order a TP-Link brand USB3 to Ethernet adapter RJ45 and see what happens. The TP-Link one is about $10 USD on Amazon.
Hi @bajaMike -
The black Yuanxin adapter is the USB to ethernet adapter. It Is NOT the reason you are having connection issues, replacing it will accomplish nothing.
You may need to replace the Fathom-X, as we communicated to you, but the first thing to check is the tether resistance. If the tether is not connected between the two Fathom-X boards, the link light will not stay on consistently. This board is sensitive to moisture, so if kept in a high humidity environment can suffer from corrosion related issues, even when protected in the FXTI box!
To troubleshoot your problem, share the resistance values you measure:
15.5 Ohms. Now what? And NO, this box was not stored in a humid environment, and always indoors. No oxidative process seen anywhere. Previous observers in the forum have commented that the board might be defective. On GitHub, there is mention of a Rev B in process. How old is Rev 2? 2016 printed on the back.
I would like to know how many of these boards have failed in the past. If sensitive to moisture why not provide a better seal in the aluminum box? But only 90 days warranty??
Hi @bajaMike -
You’re halfway there - that’s one of the tether wires resistance values, what is the other?!?!
Swapping the blue and white wires on one end of the connection may help resolve things and get the link light on steady. Otherwise one or both of the boards will need to be replaced, no way aorund it. I do notice that your pictures of the FXTI show the ethernet cable is unplugged - this must be plugged in once your link light is on ok!
Sometimes the small LX200V20 board just quits. 
The Tether Diagnostic extension in BlueOS can communicate with these boards and report their performance.
The revision history is on the product page.
Future revisions to this product will go a completely different direction using g.hn style link technology.
Our internal log of issues shows about 20 similar faults since 2020 with customers in the field. We have shipped well over 5000 units.
The warrantee is standard, and the same across all Blue Robotics products. We consider it very generous, apologies if you disagree.
Both wires measure the same 15.x ohms. So you are saying now to replace the board?
Hi @bajaMike
You could try swapping the leads as stated, or unplug the daughter board labeled LX200v and swap that between top and bottom PCB, but yes, a replacement board is likely necessary if those steps fail to get a solid steady green link light.