HDMI Quirks

[ITGURU]

Does anyone else have HDMI issues/quirks with interactive panels / projectors?

we seem to always have problems with the external devices not picking up the displays, or intermittently flickering the displays/losing connection.

We've tried several Display port to HDMI adapters as desktops don't have HDMI onboard, and even with graphics cards sometimes Extended display works ok, but as soon as try and duplicate , we get the black/blank screen on and off or just isn't stable.

 

[Steve21]

Generally that normally happens with too long cables or wrong type of cables when it's automatically trying to work out resolution etc. 

How long is the full connection from board to device? including any wall boxes/docks etc

Steve

[FN-GM]

I would bet money on this being the cables. You will need good quality cables.

 

A good AV supplier can advise more, but we have A LOT of screens and find fibre optic HDMI to be the best solution.

[ITGURU]

Most cables are 5m to get from machine to projector, odd thing is that when they are installed by supplier they use a laptop test it briefly to setup and then say its our computers that are the issue as was working fine for them.

[Steve21]

What resolution though? If they're running 1080p on a laptop and you're trying to run 4k that's very different lengths that are officially supported etc

Steve

[ITGURU]

14 minutes ago, Steve21 said:

What resolution though? If they're running 1080p on a laptop and you're trying to run 4k that's very different lengths that are officially supported etc

Steve

we change the boards etc to 1080P 30hz.

Yet at home I have a 10m hdmi from PC to TV and never have any issues! albeit a 40 inch tv 

[itskdog]

Intel iGPUs like to do the scaling on the laptop rather than the IWB (Windows shows this in "Active signal resolution" on Display -> Advanced), so tries to push 4K to our ActivPanel 6 boards while we only want 768/720p or 1080p (whatever the laptop has).

 

Lowering the refresh rate usually acts as a workaround, though sometimes I've had to switch to the Intel graphics driver rather than HP's customised one.

[Andycat]

We're finding the faceplates/tail is the blocker at the minute. All cables (Lindy) work independently at full res and 60Hz. As soon as the faceplate is in, we have to knock back to 30Hz on Extend or 2nd screen only.

[Rob_D]

5 minutes ago, Andycat said:

We're finding the faceplates/tail is the blocker at the minute. All cables (Lindy) work independently at full res and 60Hz.

In most places, we replaced most of our "terminated faceplates" with brush-pates during the last refurb. So now we can run single cables from the PC direct to the board. It's been much more reliable for us (although I don't know how much replacing the standard 3m cable loom that came with the boards would have helped on it's own).

[Andycat]

Ours has just been installed this Summer...

[synaesthesia]

Every junction/connector in a HDMI run adds a few meters worth of impedance, and some chipsets are more picky than others when it comes to signal strength. Hence a 5M run that has a faceplate adds 2 connection points, making it nearer a 10m run.

Had great success in the past using EDID emulators but at around £15 each not really a cheap solution in bulk

 

[psydii]

Yup. Anything other/additional to than the cable supplied with the screen and you are at the mercy of the gods. Fibre, though a bush plate, to the device is the most reliable.

[DrBeaker]

I don't recall VGA and it's subsets ever having as many issues/being as fussy as the 'future' HDMI standard has given us all. 😱

[psydii]

VGA cabling wasn’t trying to transmit 20-40GB/s.

 

We have, I think,  just crossed over the could/should level of video fidelity expectations.

 

We’ll see similar issues in a few years as 2.5gb/s+ switches and built-in Ethernet ports take 

hold and suddenly all those cat 5e and slightly-out-of-spec 100m cat6 runs start to suffer the same issues we see with HDMI.

 

Yesterday I replace a rogue cat 5 patch lead on a slightly over-long cat6 run solving random 200ms ping times when there was lots of network traffic on the segment. Cable and pc had been fine when they were in a different office last week… and that was on a 1g switch/pc.

[mikes]

VGA could easily output 1080p without any problems, and most use cases for HDMI here are just 1080p  not like we are trying to output 4K at 120hz.   Yet HDMI is always giving me black screens, or won't detect, especially with multi monitor setups.

We had issues with Phillips monitors, getting black screens or not being detected esp as a 2nd monitor.  Disabling QuickSync or Freesync (whatever it was called, the adaptive refresh rate option) fixed most of our issues. So might be worth going into the displays settings and checking for anything like it?

[psydii]

End points  will try to negotiate for the fastest/highest bandwidth they can both support.  If the cable can go higher than the endpoints and is in good condition, at no point does signal degradation become a factor and the negotiation is very quick.  
 

If your cables are only rated for 1080/60 and either or both end points want something faster, they try  - it takes a moment for the devices to decide to fall back to a lower bandwidth resolution/standard and try again. Rinse and repeat until the manage to get a stable setting. However (from experience) If the screen says I'm 4k60hz and the laptops also says it is, and the cable is *almost* good enough,  they don't ever fall back to something that works and you get a black or flashing screen.

On the precise mechanism for the negotiation I am not clear, but from experience if the cable outclasses the end points capabilities, you get an almost instantaneous connection/display.  

Edited September 24, 2025 by psydii

[altecsole]

On 22/09/2025 at 17:27, DrBeaker said:

I don't recall VGA and it's subsets ever having as many issues/being as fussy as the 'future' HDMI standard has given us all. 😱

You don't get audio with VGA, though. A single cable for video, and audio, makes things much from simple.

[Andrew_C]

21 minutes ago, altecsole said:

You don't get audio with VGA, though. A single cable for video, and audio, makes things much from simple.

Bringing with it the hassle of stripping out the audio if you don't want it going to a projector/board but to an amp.

[altecsole]

25 minutes ago, Andrew_C said:

Bringing with it the hassle of stripping out the audio if you don't want it going to a projector/board but to an amp.

Just use the audio output on the computer to connect to the amp and change the audio output setting on the computer. 

[Pottsey]

We found some of the cheaper HDMI cables would cause those problems. We had to replace 50+ broad HDMI cables with higher quality 4k HDMI which solved most of our problems. Another 5 to 10 boards needed extra powered HDMI. Another problem we ran into was certain laptops reduced power output to the HDMI port reducing the length of the HDMI cable so the cable would work for the desktop unit then fail for the laptop. We had to put those laptops into high power mode or keep the power supply plugged in.

 

With HDMI I think there is a balance. Those £60 gold plated PC World cables are a complete rip off. But there is a bandwidth difference between a good quality HDMI cable and the cheap budget cables.

 

EDIT: Not sure it will help, try adjusting the desktop power profile to high and see if it effects the HDMI port. 100% some laptops adjust HDMI power output. Not sure the same applies to desktops.

Edited September 24, 2025 by Pottsey

[mrstrong]

Just started to experience similar issues (flicker / no signal) in a classroom that has been fine for over a year.

Noticed the HDMI cable is bent quite a bit where it connects to the touch screen (there's no spare cable,

possibly just a 5m cable "stretched" to limit)

 

Its an old PC with intel UHD 630 Graphics duplicating the display:

 

PC | DP   -----  HDMI wall box ---- approx 5 to 6m cable run-- HDMI | Touch Screen

      | VGA ----- Monitor

 

It was running at 1920 x 1080 60Hz, I've dropped it to 1280 x 720 60Hz and seems a bit more

stable (though reporting 59Hz and active signal resolution still says 1920 x 1080 ). I did go into advanced display settings,

list all modes and tried 1280 x 720 at 30Hz but got a "control panel unable to change" error.

 

Thinking just run a 10m HDMI cable direct from PC to screen?

 

Can anyone recommend a reliable 10m HDMI cable ?

 

[psydii]

If you didn't find that pricey enough, Blustream 48Gbps AOC 8K HDMI Cable 10m (HDMI48G-10) (Black) (1) | 8K Active HDMI Cable | Richer Sounds .   If you ask a Bluestream distributor for a potential supplier you might be able to get a price closer to the off-brand offer from Adept networks.  We found Bluestream cables game changing.

[Andrew_C]

1 hour ago, altecsole said:

Just use the audio output on the computer to connect to the amp and change the audio output setting on the computer. 

And run another cable - just like VGA.  (which just works)

[psydii]

 hmdi to projector/screen. Break out from there to amp/powered speakers if necessary. Set the amp reasonably, lock it (and the audio cable runs/ports)  away so the teacher/students can't fiddle and use the computer to control volume.

 

Better though to have good speakers in the board so you don't need any external devices or additional cables.

[DrBeaker]

6 hours ago, mikes said:

VGA could easily output 1080p without any problems, and most use cases for HDMI here are just 1080p  not like we are trying to output 4K at 120hz.   Yet HDMI is always giving me black screens, or won't detect, especially with multi monitor setups.

We had issues with Phillips monitors, getting black screens or not being detected esp as a 2nd monitor.  Disabling QuickSync or Freesync (whatever it was called, the adaptive refresh rate option) fixed most of our issues. So might be worth going into the displays settings and checking for anything like it?

 

We've got good image at 1024 x 768 and especially 1920 x 1080 out of VGA before any major issues started to show. 

Occasionally it might have been slightly fuzzy at high rez/higher rez, but we've had a good 15-30m+ out of VGA before - it still worked and was usable unlike the digital HDMI whereas it's all or nothing, issues with HDCP at times etc  - I didn't think I'd miss VGA 😂

 

 

5 hours ago, altecsole said:

You don't get audio with VGA, though. A single cable for video, and audio, makes things much from simple.

 

5 hours ago, Andrew_C said:

Bringing with it the hassle of stripping out the audio if you don't want it going to a projector/board but to an amp.

 

True from a consumer point. Anything more advanced you need to essentially go backwards and split the signal display/audio which causes it's own issues.

 

3 hours ago, psydii said:

... Better though to have good speakers in the board so you don't need any external devices or additional cables.

 

You're limited to how good the TV speakers are in the flat panel screen / interactive screen though.  Unless you start putting external speakers in then to the TV.

Had some that were atrocious until we put in some external ones but the "AV pro" recommended the TV with built-in ones.