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Question Thinkpad dual 1440p monitors

Jul 12, 2021
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So I bought two 1440p monitors for my thinkpad L15 Gen 1 (i5-10210u) and thinpad 40AS dock.

As it turns out intel version of this laptop only support 1.2 display port which isn't enough to run both of them at 1440p. I tried connecting one monitor to laptops hdmi and another one via docks displayport, but it turns out that hdmi and type c port is using same video out so it doesn't work.

Then I found out that it should work if I connect one monitor through another type c port. So I bought usb-c to displayport cable which supports 4k but it still doesn't work. It does show up in windows display settings and it detects correct model but I can't enable it. If I select "extend this monitor" all screens blinks for a second and reverts to "disable this monitor". Also if I keep it connected all monitors blinks from time to time as if it's connecting/disconnecting.

I even tried to unplug dock and connect usb-c to displayport alone but it still doesn't display.

usb-c to dp cable could be broken but since they aren't cheap I would like to know for sure if my laptop supports setup like this (one monitor from dock and another from second usb-c port both at 1440p). Or maybe there's some other setups that could work? Apart from buying 40AN dock which costs almost as much as my two 27" monitors..
 

jojesa

Illustrious
The Thinkpad L15 Gen 1 supports 2 external monitors
One via HDMI with up to 4K (24Hz) and the other via USB-C with up to 4K (60Hz)

As you mentioned, the USB-C connector supports DisplayPort 1.2
The means that it supports one monitor with up to 3840 x 2160 (30Hz)
or
Two monitors with up to 1920 x 1080 pixels ( 60 Hz)

So you might have to change the resolution of your 1440p monitors

Unless that USB C to DP is tested, no one can attest of its status.
 
Last edited:
Jul 12, 2021
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The Thinkpad L15 Gen 1 supports 2 external monitors
One via HDMI with up to 4K (24Hz) and the other via USB-C with up to 4K (60Hz)

As you mentioned, the USB-C connector supports DisplayPort 1.2
The means that it supports one monitor with up to 3840 x 2160 (30Hz)
or
Two monitors with up to 1920 x 1080 pixels ( 60 Hz)

So you might have to change the resolution of your 1440p monitors

Unless that USB C to DP is tested, no one can attest of its status.
So in theory if I connect one monitor to my dock and another to hdmi both should work at 1440p? The thing is if I connect my dock and then connect another monitor via hdmi it doesn't connect at all. I can see option in bios which video output to prioritize hdmi or type-c.

Lowering resoliution would be fine (although last option) but when I connect both monitors to docks DP one monitor at 1080p is very blurry and any animations makes me almost sick.

Yeah I know that no one can test it without seeing it what I wanted to know if it should work if I connect it to my laptops usb-c I'm using this adapter https://i-tec.pro/en/produkt/c31flatdp60hz-2/
Because it doesn't work even if I disconnect everything else and connect only this it still doesn't work.
 
Jul 12, 2021
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I just tried to connect through hdmi and it works but when i attach dock it doesn't. And usbc-dp doesn't work at all dock attached or not.
 
Jul 12, 2021
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So can anyone tell me if I can connect one monitor through the dock and another through laptops usb-c to displayport?
 

jojesa

Illustrious
So in theory if I connect one monitor to my dock and another to hdmi both should work at 1440p? The thing is if I connect my dock and then connect another monitor via hdmi it doesn't connect at all. I can see option in bios which video output to prioritize hdmi or type-c.

Lowering resoliution would be fine (although last option) but when I connect both monitors to docks DP one monitor at 1080p is very blurry and any animations makes me almost sick.

Yeah I know that no one can test it without seeing it what I wanted to know if it should work if I connect it to my laptops usb-c I'm using this adapter https://i-tec.pro/en/produkt/c31flatdp60hz-2/
Because it doesn't work even if I disconnect everything else and connect only this it still doesn't work.
That adapter works with Thunderbolt 3.
Does the Thinkpad L15 Gen 1 has Thunderbolt 2 or Thunderbolt 3?
 
Jul 12, 2021
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Also I tried to connect it to samsung s20 it connected and then disconnected immediately without showing display on screen again I'm not sure if its indication of faulty cable or it shouldn't work with it.
 
Jul 12, 2021
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I solved it myself by connecting dock to second usb c port and second monitor to laptops hdmi. I assume that first usb c port shares same display output with hdmi and second has its own. It takes like 10-20 seconds for second monitor to turn on which is why I haven't noticed.
 
Reactions: Mosmos
Aug 20, 2021
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I solved it myself by connecting dock to second usb c port and second monitor to laptops hdmi. I assume that first usb c port shares same display output with hdmi and second has its own. It takes like 10-20 seconds for second monitor to turn on which is why I haven't noticed.
I have been having the same problem trying to get by 2 x 1440p displays working properly with my ThinkPad X280 and ThinkPad USB-C Dock (40A9). I took inspiration from Dunlin's idea and
  • Connected one monitor to one of the DisplayPort outputs on the USB-C docking station.
  • Connected the second monitor to the 2nd USB-C (/Thunderbolt) output on the laptop.
Every thing is working at full resolution including the l080p laptop screen.
I didn’t need to use a USB-C to Display port adapter since my monitor has a USB-C input but I suspect it would also work with one.
I was going to try a Thunderbolt Docking station next but that order has been cancelled.
 

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