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I have a laptop, with two type c thunderbolt 3 ports and an HDMI port. I have two monitors that I want to connect over HDMI to this laptop. I have a usb type c hub that has an HDMI port on it. However, when I have a monitor plugged into the type c hub, the HDMI port on my laptop doesn't send anything to the connected monitor. If I unplug the HDMI port on the hub, the monitor connected directly to the computer starts working. It doesn't matter which monitor is connected to which port. Is there any way to use both monitors at the same time?

Using the "Detect" functionality doesn't detect the other monitor while two monitors are plugged in

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Can you specify the make of your laptop and possibly the model of hub you're using? This seems like a PCI-lane issue, where the laptop is running out of lanes to drive the HDMI port once the Thunderbolt 3 ports are in use

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  • That sounds like a plausible explanation. I have a Lenovo ThinkPad x390 Yoga. My usb c hub I got a while ago and I think is a cheap chinese brand. It has 3 usb 3.0 type a ports, a type c port that supports charging (my laptop charges through it with type c), ethernet, and hdmi.
    – Jeffmagma
    Jan 21, 2020 at 3:19
  • This definitely seems like a PCIE lane issue, your Yoga X390 has 2 lanes, both of which would be used fully for the Thunderbolt 3 implementation See thunderbolttechnology.net/sites/default/files/… for details In this case, your graphics (HDMI) has no way to interface with your CPU since all the PCIe lanes are taken up by the Thunderbolt 3
    – Aadi
    Jan 21, 2020 at 3:28
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I had the same issue with the Lenova Thinkpad P52 laptop. i7 8th gen processor. All ports are located on the sides of the laptop.

Left monitor using an HDMI to USB-C cable plugged into computers USB-C. Right monitor HDMI-HDMI plugged directly into the computer HDMI.

Issues Right monitor (HDMI) will not display or register with left monitor USB-C plugged in. Removing USB-C (left monitor) allows the right monitor to come active and display content.

Fix: Simple Mistake / Easy Solution I noticed the USB-C for the monitor was plugged into the power port, and the USB-C power cord for the computer was plugged into the thunder bolt port. On the Thinkpad P52, the ports are located on the left-side and next to each other. You can power the laptop through either port. Plug USB-C power cord into the one label power and the monitor USB-C into the thunderbolt port.

Voilà...Now the monitors work.

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