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I have a 2019 Macbook Air and I use a QGeeM USB-C hub to connect to an ASUS 28" 4k monitor. The Monitor has a DP port and and 2 HDMI ports - one for 4K @ 30Hz and the other 1080p @ 60Hz. I connect to the HDMI port that supports 4k @ 30Hz. I use a Logitech keyboard with the USB dongle connected to the hub. And an Apple bluetooth trackpad. I leave the macbook screen/lid closed and connect to the hub.

98% of the time the 4k resolution on the monitor works perfectly. Every once in a while, the 4K monitor loses its resolution and I can only get 1080p. Sometimes, I can just restart the macbook, unplug and replug the display HDMI cable and everything works fine. And sometimes I end up spending an entire day trying to fix this.

I don’t understand why this happens and more importantly, How might I fix this ?

bmike
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Vasuvius
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  • There is a system utility that I have heard does a good job of switching resolution on the fly. SwitchResX at https://www.madrau.com. Though I have never used it myself I continue to read about how good it is – Steve Chambers Aug 04 '20 at 15:33
  • Use an active adapter. See this similar case: https://apple.stackexchange.com/a/354538/119271 – Allan Aug 04 '20 at 17:16
  • @Allan - I just read through the thread on 'active adapters'. So, when I used (in the past) a mini-DP (on old MBP) to DP port on the monitor, I never had any trouble. Worked perfectly always. The USB-C Hub has an HDMI port so I'm connecting using HDMI cable from the hub to the 4K HDMI port on the monitor. Do I need to replace the HDMI cable for one with an active adapter ? Or do I need to replace the hub with one that has an active HDMI adapter ? Confused. Thanks. – Vasuvius Aug 04 '20 at 18:14
  • Yes! Using mDP to DP is the best way because there's no signal conversion. I wrote a lengthy post on HDMI vs DisplayPort. You need to replace the hub with an active adapter as it's likely passive. Also, go with known brands like Anker, Belkin, TrendNet,, etc. – Allan Aug 04 '20 at 18:21
  • I'm going to tag this as a dupe since there are many questions already with these same symptoms and solutions. It can be reopened and we can continue chatting to get your problem fixed up. – Allan Aug 04 '20 at 18:38
  • Does this answer your question? Is is possible that a software issue could be causing spotty USB-C connections on 2017 MacBook Pro? – Allan Aug 04 '20 at 18:41
  • I appreciate that mDP to DP is far better. Why then do most hubs come with an HDMI port instead of an mDP port ? Is the expectation that a Thunderbolt 3 port be used with an HDMI adapter to connect to the monitor? With the older MBP having more ports, I could dedicate 1 TB (2?) port for mDP to DP connection to monitor. – Vasuvius Aug 04 '20 at 19:18
  • Now with Covid and my wife and I sharing the same desk setup at different times of day, I need to be able to plug in a single cable to my MB Air or her MBP and get everything working. I can buy a better Belkin or Anker adapter, but I'm still not fully convinced about the issue. When I check the Input choices on the monitor, sometimes, it shows the HDMI1 port as 1024x768 instead of 4K - makes no sense to me. – Vasuvius Aug 04 '20 at 19:18
  • Why? Market demand. What I believe the problem to be is the clock sync. There's one on HDMI (required) and none on DisplayPort. Your Mac natively outputs DisplayPort so there's no clock signal. The fact that a reboot fixes it is that it forces those signals to sync up, but with the lack of the clock sync, when they get out of sync, there's nothing for HDMI to "re-sync" with. – Allan Aug 04 '20 at 20:13
  • Let us continue this discussion in chat. – Vasuvius Aug 04 '20 at 20:22

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