No Signal on third monitor (LG TV)

Hello,

I have an A/V question. I just mounted 5 LG TV's in a few offices. I terminated each end to a HDMI keystone, and the length of the HDMI run is approx. 15 - 20 ft. I'm connecting the PCs to the TVs as a third monitor. Of the 5, two are working without an issue, but i'm having issues with the other three. The OS and the graphics card is detecting the TV as a third display, but after choosing the correct input on the TV, it's still displaying "no signal". This is the case for all of the displays that aren't working.

Any advice or guidance will be helpful!
Joshua Stroud, MCPIT ManagerAsked:
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Joshua Stroud, MCPIT ManagerAuthor Commented:
Furthermore, I've verified that the issue is not with the HDMI ports on the TV, as I'm able to extend the display when plugging a laptop directly into the TV.
KimputerIT ManagerCommented:
Specs of the ALL PC's and ALL the monitors?

Obviously, if they're ALL the same, it's probably the LG TV (which you could have tested by swapping the screen on a working combo, where the screen suddenly fails)

If it's all mixed up with various types and specs, it could be that you're using too high a resolution for the TV to handle it (test it by lowering it).

Saying that it's working on the laptop, therefore the TV is fine, is still not 100% correct. Still need to know the resolution of the laptop vs PC.
Joshua Stroud, MCPIT ManagerAuthor Commented:
It's mixed up, i have three Lenovo PCs and two Dell Pcs. All the TVs are LG 55UU340C devices. I'll provide the specs in a later email. As of now, one Lenovo works, and one Dell works. The setup is identical from the TV to the PC:

4' HDMI -> HDMI wall plate -> 20' HDMI cable -> HDMI wall plate
DisplayPort to HDMI adapter -> HDMI wall plate
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Joshua Stroud, MCPIT ManagerAuthor Commented:
in regards to the resolution, i'm setting the resolution to 1920 x 1080 on both devices.
David Johnson, CD, MVPRetiredCommented:
not all video cards support 3 monitors ie. 3 @ 1080p resolution.
Walk around with another laptop and confirm that the cable and tv connection work. Assuming that the cable and TV work then for those computers  that don't try a USB2HDMI adapter
Dr. KlahnPrincipal Software EngineerCommented:
4' HDMI -> HDMI wall plate -> 20' HDMI cable -> HDMI wall plate

That's a fairly long run for HDMI.  It does not help that the signal is going through two wall plates.

Bring the afflicted TVs into the same room as the computer that is feeding them, and attach them to the computer directly.  If they work in that configuration then there's a problem with the wiring.
serialbandCommented:
It would be easier to test the laptop on the TV, then test it on the long haul to verify whether the TV works from the longer connection.  If it works, then plug it back into the Desktop, but this time, just connect the single monitor/TV and unplug the rest.  Test each one, then add a 2nd, then finally add the 3rd.  That's how you can isolate the problem to the cable or video card.  Step by step, try with fewer simpler connections, then work your way up to the more complex ones.

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