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Weird video problem

H

hunterjwizzard

Veteran Member
Joined
Mar 21, 2020
Messages
1,400
This is not technically a "vintage" problem, but the fine people on this forum have shown a lovely tendency to help me do weird things. Instead of what I get on other technically-minded forums, which is people telling me "That's weird. Don't do that. Do what everyone else is doing instead."

Anyway, on to the actual problem. My main monitor is controlled by a 4 port instant-speed switcher, port 1, 2, and 4 are my workstation, gaming PC, and work computers respectively. But port 3 is connected to something called "The Snake".

The Snake is a bundle of cables which stretches the long way around the room to a shelf full of vintage computers wherein I hook up whichever one I feel like using today. I also use The Snake to hook up my test bench where I work on more modern PCs. This has worked well since the establishment of The Snake up until a few weeks ago.

The retro systems(XP, 98, and a G4) all still work fine. The XP system is even configured to 1080p and looks crisp and sharp as ever. Now, when I hook up a modern PC running windows 10 or a 10-derrived Operating system(such as server2022) the video is what can only be described as "headachy". Text is blurry and the screen acts like its on the wrong refresh rate. Its hard to troubleshoot from inside windows because, looking at it for more than a few minutes causes eye strain.

The Snake itself consists of the following: an HDMI cable goes into a stand-alone capture device(I use this to switch between 16:9and 4:3 since my monitor cannot). From the box it goes to a 4k-capable HDMI-over-cat6 extender, the other end of witch plugs into my instant-speed switcher. Everything is configured to run on 1920x1080@60hz and all equipment is capable of this.

Now here's the real rub: I can't simply bypass the switcher or any element of The Snake to use a modern PC on the switcher. If I do it fails the HDMI handshape and I have to fully unplug and power-cycle the switcher before it will work again(which plays absolute marry hell with the rest of my PCs).

So far I'm completely stuck. This feels like it must be a handshake issue, but I can't even guess why newer OSs have this problem when older ones don't. I've tried using a DVI to HDMI adapter on the newer PC graphics card vs. just going HDMI straight into it and get the same result. I've tried this on 2 different windows 10 PCs, one with a geforce 1070 and the other with some kind of ATI Radeon card and got the same result. My windows XP 32 bit machine with the triple 8800 GTXs runs perfectly on the same cable/adapter. The same test PCs all attach directly to an external monitor and work perfectly.

I should add everything worked flawlessly with everything up until about a month ago. I did not change anything physically. I had some problems with the instant-speed switcher caused by turning it off accidently, these were resolved by unplugging all 5 HDMI cables and the power supply for a few minutes. I don't know if thats related, but I've also repeated the unplug/power cycle steps with every device in The Snake.

I don't know what else to try here.
 
You have way too many variables to even try to diagnose, it could quite literally be anything.

Ground loops, power issues, ground variance, marginal power supplies, device malfunctions, EMI, cable failure, connector failure, EDID problems, pixel clock issues, etc.

It could also be Windows 10 hates whatever device its being plugged into, or driver issues. If you're using the WU version of the video drivers, stop and download the official drivers from Nvidia/AMD. You may have to make your own custom display resolution because the video card reads the available display information from the video device. Since you have so many cables switchers and extenders between the video card and the monitor, you may have to define your own custom display mode and use that.

If that doesn't work, you'll probably have to resort to tearing the whole setup down and rebuilding it from the ground up in a different, simpler manner.
 
GiGaBiTe said:
If that doesn't work, you'll probably have to resort to tearing the whole setup down and rebuilding it from the ground up in a different, simpler manner.
Click to expand...
This was my first thought but the only simplification I can make is to replace the cat6 extender with a straight HDMI cable, a distance of about 25 feet. Not impossible but that introduces other problems.
 
Plasma said:
This is the first thing I would check. My experience with various HDMI extenders over the years is that they vary greatly in quality and reliability.
Click to expand...
This one's been nicely reliable up till now, though I can switch to one of my better-quality ones for testing.

This seems to be a running problem for me. I build a setup. It works perfectly for a while. Then something happens(power outage, planned or otherwise), and I can never get it to work correctly again.
 
I swapped the no-brand extender for one made by J-Tech(whom I hope we all agree is a respectable brand) and... no change. About the only other thing I can do is trade the HDbaseT connector for a cable, which I am somewhat loathe to do. I have a lovely supply of50' HDMI cables and a long memory of endless headaches they caused me.
 
I already know things work fine when they are closer together. This is the frustrating part. Every single component works fine by itself but none of them works when all are together. And they only don't work on Windows 10.
 
hunterjwizzard said:
I already know things work fine when they are closer together. This is the frustrating part. Every single component works fine by itself but none of them works when all are together. And they only don't work on Windows 10.
Click to expand...
....then you know the issue is the HDMI extender...
 
Plasma said:
....then you know the issue is the HDMI extender...
Click to expand...
Tried that. The picture is crystal clear if I take the capture box out.

...but is also crystal clear if I take the extender out.

The line goes PC --> Capture Box --> HDMI Extender --> Switcher --> Monitor.

If I go PC --> Capture Box --> [spare] monitor(for testing), the picture is crystal clear.

If I go PC --> HDMI Extender --> Spare Monitor, the picture is crystal clear.

BUT if I go PC --> Capture Box --> Extender --> Spare Monitor it behaves the same as if going into the switcher(EG the screen gets "headachey").

Meanwhile the 3 other windows 10 computers plugged directly into the switcher all work fine.

Again every part of it works fine individually but not together. I am so stumped.

I may have to settle for a work-around. I need to expand my switching capacity anyway(want to add another PC to the rack). So I need to find a second switcher I can daisy-chain into port 3. When I do that I can simply run an HDMI cable along the snake to use. I don't LIKE doing this because the run is juuuuuuust long enough that I can't use a 25' cable. I'll be left with a crapload of service loop. But there are worse problems to have. Like the one that started this thread.
 
Near as I can figure this is caused by some interaction between windows 10, the capture box, and the video switcher. Unfortunately I seem to have broken the handshake capability again during my fiddling and won't be able to proceed until I've deep power-cycled the switcher again.

I really friggin hate HDMI handshake.

What's especially interesting here is the "handshake" seems to only be broken inside windows; the POST screen displays fine. Maybe my real problem is windows 10 just sucks.
 
hunterjwizzard said:
Tried that. The picture is crystal clear if I take the capture box out.

...but is also crystal clear if I take the extender out.

The line goes PC --> Capture Box --> HDMI Extender --> Switcher --> Monitor.

If I go PC --> Capture Box --> [spare] monitor(for testing), the picture is crystal clear.

If I go PC --> HDMI Extender --> Spare Monitor, the picture is crystal clear.

BUT if I go PC --> Capture Box --> Extender --> Spare Monitor it behaves the same as if going into the switcher(EG the screen gets "headachey").

Meanwhile the 3 other windows 10 computers plugged directly into the switcher all work fine.

Again every part of it works fine individually but not together. I am so stumped.

I may have to settle for a work-around. I need to expand my switching capacity anyway(want to add another PC to the rack). So I need to find a second switcher I can daisy-chain into port 3. When I do that I can simply run an HDMI cable along the snake to use. I don't LIKE doing this because the run is juuuuuuust long enough that I can't use a 25' cable. I'll be left with a crapload of service loop. But there are worse problems to have. Like the one that started this thread.
Click to expand...
My suggestion was: PC --> Capture Box --> short HDMI cable (6 or 10ft) --> Switcher --> Monitor

Have you tested this configuration? You should only be changing one thing at a time to troubleshoot.
 
I have not done short cable since it would involve relocating the capture box(which is normally cabled to a shelf). But I've had to move the box anyway so I'm ready to try that. Except of course now I broke the handshake ability again.

The riddle deepens: the handshake is now broken between any Windows 10 system and the monitor... but NOT other devices or operating systems. Plugged in an XP machine and it worked a treat. This sheds some interesting light on previous problems I've had with this switcher wherein I could not get one of my other computers to work through it. In those circumstances I never tried another operating system.

I cannot even speculate what weird thing inside windows 10 is creating this problem but it makes me mad.
 
Well after several more hours of dinking around with it I have actually broken the system even further. My win10 test machine will not handshake with the monitor unless I do a plugs-out reset of the core switcher. As before the problem only impacts Windows 10 computer, everything else can spit a signal through just fine. I think I'm going to focus on the win10 side of the problem, most likely a recent brute-forced update changed something about the default behavior.
 
hunterjwizzard said:
And they only don't work on Windows 10.
Click to expand...
When I worked with HDMI, I noticed that Windows 10 will always output the highest resolution to the display. Any smaller resolution you set will be scaled up by the GPU, to keep the display resolution. This may also depend on your graphics driver. Your cabling might not be able to handle the bandwidth reliably.

Normally, my go-to approach for display issues is to first reduce the resolution or frame rate to validate cabling issues, but this is tricky on modern Windows. On my test machine, the Intel driver would sometimes, and since the GPU could not handle 4K at 60 fps, any 60fps mode would force the display into 1080p60.

Regarding bandwidth values, 720p30 is about 44% of 1080p30; which is half of 1080p60; which is half of 4K30; which is half of 4K60. At those bitrates, cable quality matters a lot, and especially older cables ("high speed cable with ethernet") cannot handle HDMI 2.0/2.1 bandwidths.

Similar thoughts apply to DisplayPort as well.
 
Svenska said:
When I worked with HDMI, I noticed that Windows 10 will always output the highest resolution to the display.
Click to expand...
This is possibly a dumb question but I've manually set lower resolutions, is it possible windows is lying to me about whats actually being displayed?

The capture box is limited to 1080p60, the XP machines work fine at 1080p60. I SET the windows 10 machine to 1080p60, but is it possible its trying to pump 4k into the system since every other part of the chain supports 4k?
 
hunterjwizzard said:
This is possibly a dumb question but I've manually set lower resolutions, is it possible windows is lying to me about whats actually being displayed?
Click to expand...
Yes. Somewhere in the advanced display settings it will show the actual resolution, though.
 
that could easily be my problem. I'll pull it out and start testing again. Though at preset win10 systems arent handshaking at all. I'm looking into setting the resolution and refresh rate from the windows registry.
 
Further supporting this hypothesis: I've used a number of video downscalers in my day and this is a similar effect, at least with the blurryness. It does look an awful lot like a high resolution image downscaled(badly) to fit.
 
hunterjwizzard said:
that could easily be my problem. I'll pull it out and start testing again. Though at preset win10 systems arent handshaking at all. I'm looking into setting the resolution and refresh rate from the windows registry.
Click to expand...

There are utilities to do this for you:
customresolutionutility.net

Custom Resolution Utility - Download now!

Download Custom Resolution Utility - Download. CRU shows how the monitor defines resolutions and other capabilities and gives you the power to change it.
customresolutionutility.net customresolutionutility.net

Nvidia supports creating custom resolutions in their driver config. I think AMD does too, but haven't used an AMD video card in awhile.
 
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