Problem with HDMI through faceplates

[enjay]

We bought some new laptops recently, and those laptops don't display on our HDMI projectors, or rather, they don't display when we plug them in via the faceplates but if we plug a HDMI cable directly from the laptop to the screen it works.

 

We've ruled out cable length, as direct connections with 15 metre cables work fine.

We've ruled out cable faults, as our older laptops work fine plus the new ones work if we take the HDMI out the back of the faceplate and plug that in to the laptop.

We've ruled out faceplate faults, as we've changed those too.

 

Any ideas?!

[strawberry]

Same port? I know Epson do some funky stuff with HDMI 2

[enjay]

Same port? I know Epson do some funky stuff with HDMI 2

 

Same port and different ports.

 

So far have only tried on SMART screens, one of my team will be trying an affected laptop on a different brand of screen shortly to see if we can narrow this down to a board or laptop problem.

[SamanthaD]

Any break in the chain causes resistance and so effectively adds cable length. So if you have a 10m lead going from the projector to the faceplate, there will be a break as it goes to the faceplate pigtail, a 10cm lead, another break at the faceplate itself, then another 2/3m lead to the laptop. These breaks could add up to anything to an effective cable length of around 20m.

 

I suggest swapping the faceplate out for a brushplate, and just using the cable that would go into the faceplate direct into your laptop as you have already done in your testing.Removes 2 breaks in the chain and means you don't lose any flyleads!

 

Failing that you'll need a cable equaliser to amplify the signal.

[enjay]

I suggest swapping the faceplate out for a brushplate, and just using the cable that would go into the faceplate direct into your laptop as you have already done in your testing.Removes 2 breaks in the chain and means you don't lose any flyleads!

 

In some rooms that would be okay, but others have rather expensive (HDMI-to-fibre converter) cables running from the faceplate to the screen, so I'd rather not have staff plugging and unplugging a £150 cable every lesson. I also wouldn't want staff leaving the fibre cable lying around on their desk to get squashed and damaged.

[SamanthaD]

In some rooms that would be okay, but others have rather expensive (HDMI-to-fibre converter) cables running from the faceplate to the screen, so I'd rather not have staff plugging and unplugging a £150 cable every lesson. I also wouldn't want staff leaving the fibre cable lying around on their desk to get squashed and damaged.

Sorry, the way you wrote it I thought you were using copper to the projector, not doing more conversions etc. Guess running new cabling is out of the question?

 

Either that or the only other link in the chain is the flylead? Mind you if you're saying this setup worked with older laptops but not your newer ones, then it might be a resolution issue - are the laptops trying to push out 4k to the projector?

[enjay]

Sorry, the way you wrote it I thought you were using copper to the projector, not doing more conversions etc.

 

Some of the projectors are copper others have fibre converters, but neither of them work.

 

Guess running new cabling is out of the question?

 

We can't replace the fibre converters with copper, they're going through under-floor conduits which are too narrow for HDMI cables. But since the copper ones are affected too, I don't see it would help.

 

 

Changed those too.

 

Mind you if you're saying this setup worked with older laptops but not your newer ones, then it might be a resolution issue - are the laptops trying to push out 4k to the projector?

 

Not 4K but it is big, because they're 75" SMART screens so it is giving out 3200xsomething-or-other. The resolution itself is okay though because if we connect directly on the fibre it works, but I think you're in the right area though, as we've since found out a direct connection on a long HDMI doesn't work but the long fibre does. So resolution isn't the issue but cable quality or signal strength could be.

[enjay]

Not 4K but it is big, because they're 75" SMART screens so it is giving out 3200xsomething-or-other.

 

Actually, they are 4K (3840x2160 is 4K, right?). Is that significant?

[bald_pig]

Actually, they are 4K (3840x2160 is 4K, right?). Is that significant?

 

4k uses more bandwidth, dropping the resolution will help. Don't forget you need HDMI 1.4 compliant cables for 4k30 and 2.0 cables for 4k60.

[enjay]

4k uses more bandwidth, dropping the resolution will help. Don't forget you need HDMI 1.4 compliant cables for 4k30 and 2.0 cables for 4k60.

 

I'm wondering if that's it - the installers didn't put the right grade of HDMI cable through the walls or in the faceplates. That would explain a lot of the results we've had so far. I've bought some HDMI2.0 cables and will test...

[SamanthaD]

Actually, they are 4K (3840x2160 is 4K, right?). Is that significant?

 

3840 x 2160 is technically UHD, not 4k which is 4096 x 2160. But as that doesn't fit in with the 16:9 ratio we all know and love, UHD has had the "4k" label stuck on it, thanks mainly to consumer products.

[enjay]

Okay, we've done some more testing. Turns out the faceplate isn't suitable, the spec says it can send 4K for 3 metres - nice of the supplier to tell us this when selling and installing them with a 10m metre cable pack...

 

It works fine if I plug straight in to the cable, but I don't really want staff plugging their laptops in to such expensive cables. If I put any other fly-lead in the way, I need to also use a powered repeater. So, for now at least we'll either buy powered repeaters and tuck them away behind a brush plate as per @SamDavis earlier suggestion, or give the affected staff 5m HDMI fly-leads and tell them to connect direct to the screens.

 

Hopefully the supplier will come up with something cleaner (so far their response has been to say not many schools use 4K so they didn't bother to tell me about the limitation - not impressed!) but this will do for Day One next week.

[Passat1983ICTech]

hi there have you check the drivers are update check the screen realisation

[enjay]

hi there have you check the drivers are update check the screen realisation

 

Drivers are good, the issue is physical. The image is fine if you plug in directly to the screen, or even if you plug in to the HDMI cable which is normally in the back of the faceplate, it just just doesn't work when you got through the face-plate.

[mavhc]

If you change the resolution on the laptop to be not 4k, does it work?

[enjay]

If you change the resolution on the laptop to be not 4k, does it work?

 

Yes, if you pull it low enough, but staff don't have the rights to do that, plus they often teach in multiple rooms and therefore need their laptops to auto-detect the optimal screen settings for the location.

[localzuk]

In some rooms that would be okay, but others have rather expensive (HDMI-to-fibre converter) cables running from the faceplate to the screen, so I'd rather not have staff plugging and unplugging a £150 cable every lesson. I also wouldn't want staff leaving the fibre cable lying around on their desk to get squashed and damaged.

 

Could you not hide the converter cable in trunking and have a HDMI coupler and short cable plugged in to it coming out of a brush plate?

[enjay]

Could you not hide the converter cable in trunking and have a HDMI coupler and short cable plugged in to it coming out of a brush plate?

 

That's probably what it will come down to. We need to get powered repeaters/boosters in too.

[psydii]

Have you tried with DisplayPort, if your screen have it.? Allegedly it negotiates the maximum resolution based available conditions so should revert to 1080p in cases where the cabling wouldn’t support 4K.

 

DP is available through the USB C port of most modern laptops.

[enjay]

Have you tried with DisplayPort, if your screen have it.? Allegedly it negotiates the maximum resolution based available conditions so should revert to 1080p in cases where the cabling wouldn’t support 4K.

 

DP is available through the USB C port of most modern laptops.

 

I don't think the screens have DP, but I'll check. What cables would I need if they do?

[mavhc]

Other thing to test would be some kind of socket-socket back to back, instead of the short cable

[psydii]

I don't think the screens have DP, but I'll check. What cables would I need if they do?

 

To quote a reply from VESA in response to a question about DP limitations in a dock/4k screen classroom-based scenario:

 

If you are referring to cable length, optical solutions are available up to 100 meters. If bandwidth, many USB-C docks operate in a "2+2" configuration, where 2 of the high-speed lanes in the interface are used for DisplayPort and 2 are used for superspeed USB. In this config, if your source supports DP High Bit Rate 2, you can expect up to 4k @ 30Hz. But if using a 15m passive cable, the DisplayPort link will likely train to High Bit Rate and resulting resolution will be 1080p. The DisplayPort link will train to whatever condition works regardless the max supported data rate, often (incorrectly) referred to as DP 1.4, 1.2... DP is controlled by the graphics driver and results may vary with Intel, AMD, Nivida.

(my emphasis)

 

The terms in the above are explained here:

https://www.displayport.org/cables/how-to-choose-a-displayport-cable-and-not-get-a-bad-one/