Apple hardware has stymied me for the first time
January 8, 2020 11:20 PM Subscribe
Up until about a month ago, I had a 2014 Macbook Pro and I had no problem using two additional large monitors. Neither of them is fancy, only one is 4K.
I've acquired a 2019 Macbook Pro (16") and I can't get both monitors to handle input at the same time.
I have an Asus VS248 whose max resolution is 1920 x 1080. Its input ports are:
- HDMI
- DVI
- VGA
I also have a Dell P2415Q whose max resolution is 3840 x 2160 which I understand to be 4K. Its ports are:
- Display port (the one that looks like an HDMI port with an extra corner) - input and output
- mini Display port
- HDMI (MHL)
- USB 3.0
With a 2018 model of this laptop - borrowed from a previous employer - I had no problem using these two monitors together with a cheap unpowered hub. This was 1 x HDMI and 1 x VGA.
I bought a powered hub - an Elgato Thunderbolt 3 - and I still can only use one monitor and it doesn't seem to be charging the laptop.
What am I missing?
I have an Asus VS248 whose max resolution is 1920 x 1080. Its input ports are:
- HDMI
- DVI
- VGA
I also have a Dell P2415Q whose max resolution is 3840 x 2160 which I understand to be 4K. Its ports are:
- Display port (the one that looks like an HDMI port with an extra corner) - input and output
- mini Display port
- HDMI (MHL)
- USB 3.0
With a 2018 model of this laptop - borrowed from a previous employer - I had no problem using these two monitors together with a cheap unpowered hub. This was 1 x HDMI and 1 x VGA.
I bought a powered hub - an Elgato Thunderbolt 3 - and I still can only use one monitor and it doesn't seem to be charging the laptop.
What am I missing?
Are you using the correct cable to hook the laptop to the hub? It has to be a Thunderbolt 3 rated charging cable IIRC. A random USBC cable isn’t going to cut it.
Thunderbolt can be a tad finicky in my experience. What cables are you using to connect these devices & what’s the topology exactly?
posted by pharm at 3:50 AM on January 9, 2020
Thunderbolt can be a tad finicky in my experience. What cables are you using to connect these devices & what’s the topology exactly?
posted by pharm at 3:50 AM on January 9, 2020
Best answer: NB Elgato says that the DIsplyport socket on that Hub can’t do 4k@60Hz using the Displayport output with your monitor: https://help.elgato.com/hc/en-us/articles/360028239711-Can-Elgato-Thunderbolt-3-Dock-use-4K-or-5K-displays-
You have to either downgrade the DisplayPort version on your monitor & accept 4K@30 Hz or switch to a Thunderbolt->Displayport active cable.
posted by pharm at 3:57 AM on January 9, 2020
You have to either downgrade the DisplayPort version on your monitor & accept 4K@30 Hz or switch to a Thunderbolt->Displayport active cable.
posted by pharm at 3:57 AM on January 9, 2020
Best answer: I am going to be watching this space, in case someone has a different solution, but I will share what I learned in case it helps.
I have the 2019 MacBook Pro 13”. I also have 2 monitors with similar options to yours hooked up at work and I had similar issues. My issues looked like either one monitor only working sporadically or both monitors displaying the same screen.
When I looked into it further, it looked to me like the Thunderbolt ports were only able to support one non-Thunderbolt based monitor per port. When I reconfigured my setup so one monitor was hooked up to the hub and one was hooked up directly to the other Thunderbolt port via a Thunderbolt to HDMI adapter, the issues stopped. I hope that helps.
posted by eleanna at 4:13 AM on January 9, 2020
I have the 2019 MacBook Pro 13”. I also have 2 monitors with similar options to yours hooked up at work and I had similar issues. My issues looked like either one monitor only working sporadically or both monitors displaying the same screen.
When I looked into it further, it looked to me like the Thunderbolt ports were only able to support one non-Thunderbolt based monitor per port. When I reconfigured my setup so one monitor was hooked up to the hub and one was hooked up directly to the other Thunderbolt port via a Thunderbolt to HDMI adapter, the issues stopped. I hope that helps.
posted by eleanna at 4:13 AM on January 9, 2020
(Which has had no problem charging the laptop.) I will show myself out now.
posted by eleanna at 4:17 AM on January 9, 2020
posted by eleanna at 4:17 AM on January 9, 2020
When I reconfigured my setup so one monitor was hooked up to the hub and one was hooked up directly to the other Thunderbolt port via a Thunderbolt to HDMI adapter, the issues stopped. I hope that helps.
Echoing that I also use this setup and it works well. A little annoying to plug in two things, but not unbearably so.
posted by mosst at 5:22 AM on January 9, 2020
Echoing that I also use this setup and it works well. A little annoying to plug in two things, but not unbearably so.
posted by mosst at 5:22 AM on January 9, 2020
Each pair of Thunderbolt sockets on the Macbook share a Thunderbolt PCIe channel & you can’t run two 4k@60Hz displays from one channel I believe. (The fine details depend on actual resolution & bit depth of the display.)
posted by pharm at 5:52 AM on January 9, 2020
posted by pharm at 5:52 AM on January 9, 2020
Response by poster: pharma, thanks for the link to the documentation. I was getting so frustrated that I didn't even look at their docs. I tried most of the things related to my equipment with no luck.
As a last-ditch effort, I restored the setup to what it was before I got the powered hub and it works great again.
Here's what works for me: I have a DisplayPort to USB-C cable going from the Dell (the 4K) into one of the USB-C ports on the laptop. The other monitor has an HDMI to HDMI cable plugged into the cheap unpowered hub.
I don't know why this setup stopped working suddenly but I guess I just needed to wiggle the plugs more or try turning it off and turning it on again and now it works again.
I'm still unclear on the difference between Thunderbolt and USB-C so I'll have to do some googling for that.
Thanks for your help y'all. I hope the comments in here help someone else.
posted by bendy at 6:32 PM on January 9, 2020
As a last-ditch effort, I restored the setup to what it was before I got the powered hub and it works great again.
Here's what works for me: I have a DisplayPort to USB-C cable going from the Dell (the 4K) into one of the USB-C ports on the laptop. The other monitor has an HDMI to HDMI cable plugged into the cheap unpowered hub.
I don't know why this setup stopped working suddenly but I guess I just needed to wiggle the plugs more or try turning it off and turning it on again and now it works again.
I'm still unclear on the difference between Thunderbolt and USB-C so I'll have to do some googling for that.
Thanks for your help y'all. I hope the comments in here help someone else.
posted by bendy at 6:32 PM on January 9, 2020
Response by poster: mewsic, I never figured out if the hub was actually working! I never saw it charging and the stupid UX doesn't even include a power indicator light.
posted by bendy at 6:36 PM on January 9, 2020
posted by bendy at 6:36 PM on January 9, 2020
Best answer: Thunderbolt is essentially a signalling protocol which happens to use USB-C cables as physical infrastructure.
eleanna: That would make sense. When you plug a displayport or HDMI adapter cable into a thunderbolt socket it negotiates with the socket it put it in an alternate (non-thunderbolt) mode which channels the signal from a displayport output on the video chip out through the socket.
So you can't connect more than one displayport (or HDMI) output to a single thunderbolt socket, because connecting the cable effectively converts the socket into a weirdly shaped single DisplayPort output. What you can do (I think) is daisy chain thunderbolt displays from a single socket, just as you can with an ordinary DisplayPort output. But you’re still bandwidth limited in this case - you can't daisy chain two 4k displays at 60Hz IIRC (at least, not until the next generation of video hardware that supports the new version of DisplayPort anyway).
posted by pharm at 1:47 AM on January 10, 2020
eleanna: That would make sense. When you plug a displayport or HDMI adapter cable into a thunderbolt socket it negotiates with the socket it put it in an alternate (non-thunderbolt) mode which channels the signal from a displayport output on the video chip out through the socket.
So you can't connect more than one displayport (or HDMI) output to a single thunderbolt socket, because connecting the cable effectively converts the socket into a weirdly shaped single DisplayPort output. What you can do (I think) is daisy chain thunderbolt displays from a single socket, just as you can with an ordinary DisplayPort output. But you’re still bandwidth limited in this case - you can't daisy chain two 4k displays at 60Hz IIRC (at least, not until the next generation of video hardware that supports the new version of DisplayPort anyway).
posted by pharm at 1:47 AM on January 10, 2020
Response by poster: As a last follow-up: the HDMI-to-HDMI cable between the 1920 x 1080 monitor and the unpowered hub would disconnect if I so much as breathed on my desk and it would take a few seconds to unplug everything and plug it back in.
I switched that monitor connection back to VGA-to-VGA and both ends are screwed in tight and the picture on the monitor is much sharper and has better colors.
posted by bendy at 11:01 PM on January 15, 2020
I switched that monitor connection back to VGA-to-VGA and both ends are screwed in tight and the picture on the monitor is much sharper and has better colors.
posted by bendy at 11:01 PM on January 15, 2020
Response by poster: If anyone is still following this, I finally found a solution. Two DisplayPort to USB-C cables. I got these and so far no problems at all. I tried daisy-chaining but with no luck. Finally, though, all is good. HTH HAND.
posted by bendy at 2:48 PM on February 9, 2020
posted by bendy at 2:48 PM on February 9, 2020
Response by poster: Also, the newer monitor has high-powered USB ports on the back so I can finally ditch my dongle.
posted by bendy at 2:51 PM on February 9, 2020
posted by bendy at 2:51 PM on February 9, 2020
« Older What are your favorite (available online) Prince... | I want to make an original, catchy rap song, where... Newer »
This thread is closed to new comments.
Have you verified that the hub is working? I only ask this because they advertise that it will charge the laptop, so if it's not doing that then it, or the cable between them, is likely borked. You can tell by the battery icon in the menu bar - it has a lightning bolt through it when it's charging I think.
Other than that, my troubleshooting techniques involve known good equipment where possible, so can you get the "cheap unpowered hub" for a test? If you can get it to work on the new computer with the other hub then it pretty much has to be the Elgato hub. I would be checking cables too. And input settings on the monitors. Everything you can, no matter how unlikely you think it is.
Also, are you able to elaborate on what "still can only use one monitor" means? as in, what actually happens when you connect the second one?
posted by mewsic at 3:42 AM on January 9, 2020