Well-above my head with KVM switch and DisplayPort repeaters

Hi all! I am new to the forum, but I am a fan of the Level1 YouTube channels.

I have been agonizing over a very, very specific situation for the past year and I don’t know where else to look. I am relying on the experiences of the like-minded community here…!

I am using VFIO with one monitor via a KVM. My KVM is the StarTech SV431DPUA. The monitor supports DisplayPort 1.4, but the KVM only supports DisplayPort 1.2, if that is relevant.

I was surprised when I started using the KVM that my display was not being detected properly and I couldn’t get any OS to detect my desired refresh rate and resolution correctly. I gather, from disparate web results, that this is due to the KVM not communicating the EDID signal properly. Is this correct?

Assuming it is related to EDID, I have also figured out that a solution might be to purchase a DisplayPort EDID repeater dongle. But I don’t really understand how this works. Do I need a separate repeater for every DisplayPort output of the KVM, or do I need just one from the monitor to the KVM?

I would prefer not to buy a new KVM 1) because I have one, and 2) because it’s not easy to obtain in Japan where I live. And I would prefer not to buy a repeater only to find out the task is just impossible.

I noticed some posts on the forum related primarily to DisplayPort cables. My cables are cheap StarTech ones so I wouldn’t necessarily be surprised if that were the issue instead.

Any help would be greatly appreciated!

I’m not 100 familiar with the internals, there’s folks here who know KVMs inside and out.

I’ve always imagined KVMs as mostly “dumb” / mostly analog switches rather than anything that would decode/reconstitute the signal - which is why cables would play a big role.

I have had good luck at home with Amazon basics, elecom and ivanky cables, I’ve chucked some 3m startech cables my company provided for me into the bin this weekend (I use a startech KVM too, but a different model)

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I’m not an expert, but I do use a Level1Techs KVM and EDID Repeater. I am doubtful that an EDID repeater would satisfy your need.

An EDID repeater goes between the KVM and the computer. So you would need a repeater for each computer DisplayPort that you wish to “fix”. The repeater learns the EDID from the monitor, so the signal must pass through the KVM. That seems to be where your setup is having difficulty. The repeater then constantly presents the EDID to the computer, so the computer doesn’t notice when the KVM is switched away.

It is possible that an EDID repeater might have better luck getting the EDID from the monitor, through the KVM. But that seems like a slender hope since the purchase process is difficult in your circumstances.

My guess is that replacing the KVM might be a better technical solution, but I respect that you prefer not to do this. I had had good experience with the Level1Techs KVM, and recommend it if you change your mind. My EDID repeater does work with a monitor on the other side of the L1T KVM. But from what you say, I doubt the repeater would work with your KVM.

Best of luck on finding a satisfactory resolution.

What monitor?

What attempted resolution, refresh rate and color depth?

What cables are you using and what is the total run length (including any thunderbolt/usb cables going into a dock)?

To expound a bit on why I asked the questions; many displayport cables are not actually in spec, which can cause higher bandwidth signals (as are needed to carry higher resolutions or refresh rates) to degrade past the point of being capable of being decoded.

To this end, many people have found, while using the Level1 KVM, that keeping the total length of the cables (on the PC → KVM side and the KVM → Display side combined) under 4 meters. Part of the problem here is that most KVMs are just switching mechanisms, and do not actually condition or repeat the signal.

This 4 meter run length has been reproduced by myself on my system, but has only been successful (at [email protected]) when using either cables provided from the Level1 store, or genuine Club3D cables. All other cables I have attempted to use have failed to maintain signal integrity.

Hope this helps; I’ll monitor this thread.

That’s a bummer, but you are probably right. I guess there are not so many power users that really want the kind of KVM setup that I do, so purchasing a new KVM might be the easiest and best solution.

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This is very helpful, thank you! :smiley:

  • Monitor: Samsung C27HG7x
  • Monitor settings: 2560x1440, 144Hz
  • Cables: Startech 3m DisplayPort 1.4 (DP14MM3M)
  • Stuff attached to KVM: Two ports for a fancy RGB keyboard, which itself has USB passthrough (I attach a mouse to the keyboard, and the keyboard to the KVM). I also have a USB microphone and webcam attached to the KVM. My only requirement is the mouse+keyboard, the webcam+mic are just nice to have.
  • Other stuff attached to monitor: There are some USB ports that I use to charge my phone primarily.

The cables aren’t like, Amazon Basics tier, but they could be the problem. I guess 1440p 144Hz is sort of out of the KVM’s specs, but I read some conflicting reviews on Amazon Japan where people said they had it working…

Since the display was not being detected properly (on Windows or Linux), I figured I could force it to work through a repeater. If that’s not the case, maybe it is best to cut my losses and get the KVM I really need.

You have a total run length of 6 meters, which is probably where your trouble is coming from.

Its possible, but buying proper cables will be a much cleaner approach and will probably cost less. I highly recommended trying that first, with either the club3d cables or the ones on the Level1 store. (I use a combination of both)

Its not that the cables are bad, its that they are not designed to take into consideration the additional degradation of a KVM and additional cable run length, so at 3m total, it is fine, but when its 3m+KVM+3m, it is not fine.

Mmm. I see. Well, it can’t hurt to try! I will report back on how it goes.

Thanks again!

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These are the ones I threw out recently.

Believe it or not, Amazon basics are actually better.


Remember that your maximum combined run should not exceed 4m, so the 3m cables should be replaced with 2m cables if possible. Anything beyond that, and I’ve experienced failures.

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Hi all!

As promised I finally made it to the local computer store. I bought two 2m DisplayPort cables (1.4 this time, if it matters; I assume that being rated for 1.4 can only improve the signal-to-noise ratio).

Unfortunately the issue persists. I get the distinct impression that I have simply purchased the wrong device for my needs: if I need a KVM that supports high-resolution high-refresh rate displays, then I should have sprung for the real deal when I made my purchase last year. Now I am left with an expensive USB switching KVM. Not the worst thing, at least.

I think what will be best for me is to buy a second monitor at this point.