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Mac: LG B9 and Cable Matter USB C to HDMI Blanking and CalDigit TS4 Dock

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Argh, this has been so annoying over the last two years. I have an LG B9 television connected to a MacBook Pro M1 2021 and most of the time when I turn it on, the MacBook is not detected. Here are the symptoms:

  1. When I turn on the TV and plug in the Mac, I will get no signal found.
  2. I find that if I go to the Dashboard and switch to the TV signal and then back, most of the time the signal comes back.
  3. Sometimes, I can't tell when the signal will disappear, the screen goes blank, and then it returns in a few seconds.
  4. Also with MacOS Ventura out, I'm also finding that when playing the audio, it gets very glitchy and strange, like the output is not in sync. This is going through the Thunderbolt 3 dock through a Cable Matters USB C to HDMI adapter into the LG B9 and then the output is through the optical output to an old Denon AVR. You can see how it is hard to debug such a long chain
  5. The really strange thing is that the Mac detects the monitor and goes into multiple screen mode, but the LG says there is no signal, it sure looks like there is a handshake problem and maybe the USB C to HDMI is not quite right.

It sure feel like, the Mac is losing synchronization with the HDMI input of the B9, but which of the many devices is at fault, the Mac, the Cable Matters, the LG, or the Denon?

I can't find anything about this on the web, so the debugging worked like this for future reference, the key thing is to keep taking devices out and then seeing what works.

  1. I have a Razer Thunderbolt 4 dock, so I removed that. This didn't help. I do have a new Caldigit TS4 Thunderbolt 4 dock ordered, so I can try that when I get it, my Caldigit TS3 have been really reliable, so it will be nice to be all Caldigit and I look forward to having the DisplayPort output directly and lots more ports for it.
  2. I removed the Cable Matters USB C to HDMI adapter and plugged the HDMI directly into the Mac and the screen comes on every time.

So it seems like the problem is the Cable Matters USB C to HDMI adapter. This is a high-end 48Gbps HDMI 2.1 compatible connector and the HDMI input on the LG B9 is also HDMI 2.1. However, the issue seems to be with the USB C DisplayPort mode to HDMI conversion, so off to find:

  1. Google-fu has failed me on this, I've found lots of generic advice about USB C to HDMI and generic advice about displays not showing as well as generic Cable Matters advice. They do point to a Synaptics DisplayLink Manager for Mac which I've never heard of but will try to download. And there is apparently a magic force display detection. But nothing that really covers this.
  2. So I'm thinking its time to try more USB C to HDMI adapters as an experiement or even a DisplayPort to HDMI with the Caldigit.
  3. Yes, I can just plug in the HDMI into the Mac (glad it has one), but the whole idea is one cable to connect power and everything else 🙂

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