[SOLVED] VGA no signal when plugging in USB-C

baileyboy125

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Jul 27, 2015
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Hi,

I used a Dell Latitude 5490 for my work (provided by my organisation) which has a USB-C displayport, HDMI and VGA.
I've been using 2 monitors connected to the USB-C and HDMI, but have been wanting to use a third display. I'm currently having issues doing this as when I have the USB-C connected, the third monitor with VGA recieves no signal, but as soon as I unplug the USB-C I get a signal. When I plug the USB-C back in I lose VGA signal.

I've tried different monitors, different VGA cables, updating drivers, restarting, checking display settings, but nothing seems to work having all 3 monitors working at the same time.
 
Internal wiring of the system and its onboard display output connectors means only two physical outputs can be allocated display bandwidth from the GPU at a time. Your only option would be to leverage the fact that a DisplayPort/USB-C is capable of driving multiple independent displays from a single physical connector, then attach at least two displays to that connector. There are a few ways to use that capability:

Use DisplayPort daisy-chaining for at least two of your displays, assuming at least two of your displays have DisplayPort inputs and at least one of them has a DisplayPort output to support daisy-chaining

Use a DisplayPort MST hub. StarTech has models with 2 and 3 outputs and DisplayPort and HDMI outputs here, although you can probably find better prices through retailers like Amazon. If you decide to get the DisplayPort output version and need to use HDMI/DVI displays as well, make sure you buy active DisplayPort to HDMI adapters. Most DP to HDMI adapters are passive, and those typically won't work with MST hubs. Essentially, you can do dual 2560x1600 displays or up to 3 1920x1200 displays.

Use a USB-C dock. USB-C dock actually gives you less display bandwidth than the MST hub option described above, since now your USB-C port is required to carry both display and USB 3.0 data, but you could still get dual displays up to 1920x1200 out of it, and of course you get other connectivity benefits of a dock.
 
Internal wiring of the system and its onboard display output connectors means only two physical outputs can be allocated display bandwidth from the GPU at a time. Your only option would be to leverage the fact that a DisplayPort/USB-C is capable of driving multiple independent displays from a single physical connector, then attach at least two displays to that connector. There are a few ways to use that capability:

Use DisplayPort daisy-chaining for at least two of your displays, assuming at least two of your displays have DisplayPort inputs and at least one of them has a DisplayPort output to support daisy-chaining

Use a DisplayPort MST hub. StarTech has models with 2 and 3 outputs and DisplayPort and HDMI outputs here, although you can probably find better prices through retailers like Amazon. If you decide to get the DisplayPort output version and need to use HDMI/DVI displays as well, make sure you buy active DisplayPort to HDMI adapters. Most DP to HDMI adapters are passive, and those typically won't work with MST hubs. Essentially, you can do dual 2560x1600 displays or up to 3 1920x1200 displays.

Use a USB-C dock. USB-C dock actually gives you less display bandwidth than the MST hub option described above, since now your USB-C port is required to carry both display and USB 3.0 data, but you could still get dual displays up to 1920x1200 out of it, and of course you get other connectivity benefits of a dock.
 

baileyboy125

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Jul 27, 2015
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Oh right, thanks. I’m actually using 2 Dell UltraSharp U2415 which has a Mini DisplayPort IN, DisplayPort IN and a DisplayPort OUT, which has MST support, so I could technically daisy chain all my monitors.
Didn’t know about this haha. Once I get another cable I’ll try it out. Thanks again Kerberos.
 

baileyboy125

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Update:
Daisy-Chaining does work and it does detect all 3 additional monitors, however I can only have 2 of these active a one time. One of them has the option 'Disconnect this display' under the 'multiple displays' dropdown. When I change it to 'extend desktop to this display', the display works but then one of the other ones is set to 'Disconnect this display', and the cycle repeats. Any ideas on this?
 

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