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Belkin 2m TB3/USB C cable not working w tbMBP

Arthur75

Arthur75

macrumors 6502
Original poster
Mar 9, 2015
462
301
paris, france
I just received my tbMBP 13" 2016 and an LG 27UD88 monitor (4K 27" with USB C TB3 connection).
Quite happy about both, but a strange thing happened : the display is working perfectly with the provided USB C cable, but as it was a bit short for my set up, I bought a 2 meters belkin USB C TB3 cable (in an apple store), and it does not work with this Belkin cable..
The display is not recognised by the MBP apparently, and the display does not receive any signal.

Anybody encountered a similar issue ?

Will bring the cable back tomorrow ...
 
I used a TB3-specific cable (.5m from CalDigit) with the LG 27UD88 and my '16 MacBook. Worked fine.
 
Here's what's happening:
  • As @filman408 said, your display uses USB-C, not Thunderbolt 3. The connectors look the same but USB-C and Thunderbolt 3 are different.
  • Most Thunderbolt 3 cables are backwards-compatible with USB-C. This means if you use most Thunderbolt 3 cables to connect your tbMBP to your USB-C display, it would work. However, the 2 metre Belkin Thunderbolt 3 cable is one of the very few Thunderbolt 3 cables not fully backwards compatible with USB-C. This is for complicated reasons, read below if you are interested.
  • You may be able to find a longer USB-C cable on the market that will work, but it is not guaranteed. You need one that will support USB 3.1 - i.e. not just a charging cable.
---

The reasons for the Belkin 2 metre Thunderbolt 3 cable not being backwards-compatible with USB-C, for those who are interested:
  • The full 40 Gbps Thunderbolt 3 speeds are only attainable over 0.5 metres using conventional cables at present. This is why if you look at Thunderbolt 3 cables that are longer than 0.5 metres from manufacturers such as Kanex and Plugable, they are limited to 20 Gbps.
  • The Belkin cable, however, is 2 metres long and supports the full 40 Gbps. How can this be?
    • It is an active cable, meaning there are complex chips inside that manipulate the signals at each end of the cable.
    • The actual cable part is fibre optic, which has the benefit of working over longer distances than copper without slowdown. The cable turns the Thunderbolt 3 signal into something that can be sent over fibre optic, transfers that signal down the fibre cables, and then converts it back into a conventional Thunderbolt 3 signal at the other end.
    • This is extremely advanced stuff and appears to be a special collaboration between Belkin and Apple to achieve this. However, because it uses fibre cables it loses its USB-C backwards-compatibility.
    • This is why the cable is so expensive.
 
Thanks for the detailed info, so there is a laser in this cable ?! Indeed the ends are a bit bigger than usual, but effectively I didn't find a USB-C around 2 meters yet, hope some will come up (or I will have to use hdmi), or something prevents USB C (3.1) to be 2m long ?
 
Arthur75 said:
The specs says : "Please note for USB-C usage this cable is limited to USB 3.1 Gen 1."
So maybe it will not ?
I have to check if I can get 60hz over hdmi with that display, then I will probably go that route, once I get a proper docking station/hub
Click to expand...
I had a Google and it appears Gen 1 can support your display. There aren't any Gen 2 cables that are longer than about a metre.
 
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