Using HDMI source on DisplayPort 1.4 KVM

Level1 Store KVM Helpdesk
1

KVM Model:

4 computer, 2 display L1 KVM

USB Interface (5-gigabit or 10-gigbit):

5GB

Problem:

I’ve got 2 computers, a PC and a Mac, connected to Ports 1 and 2 respectively on my KVM. The PC is connected directly to the KVM, while the Mac is connected to a Dell TB dock, then to the KVM. The KVM is connected to an LG 38GN950-B. For the most part, these two computers work as expected. (I’m experiencing static on my PC, but I’d like to resolve this issue first, and then I’ll circle back on that.)

Where I’m running into an issue is when I try to connect another HDMI PC to the KVM. I’ve tried both my Surface Pro 3 (using their mini-DP-to-HDMI adapter) to an active HDMI-to-DisplayPort converter, to the DisplayPort cable running to my KVM, as well as a new Framework 13 computer, connecting the HDMI port via HDMI cable to the active HDMI-to-DisplayPort converter, then to DisplayPort cable to KVM.

I’ve tried 2 difference converter boxes, a Cable Matters converter and a BENFEI converter. When I connect either the SP3 or Framework 13 via HDMI, the monitor is detected by Windows, but there’s no output, regardless of resolution change, refresh rate, or mirror vs. duplicate. I’ve also tried swapping ports on the KVM, with no success, and tried swapping out the DisplayPort cable to a different, fiber-optic one.

I feel like this can’t be such a unique setup that I want to connect an HDMI source to a DisplayPort KVM, right? Has anyone encountered this setup before? What cable or converter box have you used that have 100% solved this issue?

Other Notes:

It’s rare I use this setup. My plan for this was something of a bench setup, where if I’m working on a friend’s computer, I plug an HDMI cable and USB cable into their computer and swap my KVM over to Port 4 and just continue working on my monitor and keyboard. I could have sworn that this setup originally worked when I started, which was why I purchased a new/different converter box. When I wired this probably a year ago, I would have tested it with my SP3, and my memory is fuzzy there, but I remember thinking “awesome, this works, and I’m good for the future.” A few months back I tried to hook it up and it didn’t work, and my thought was, “Damn, I thought this worked, maybe the mini-DP port on my SP3 is going bad, it is old.” But then I got this new Framework and realized it didn’t work either and figured something went bad or it never worked, and I’ve gone down the rabbit hole trying to solve it. Like I said, maybe I’m mistaken and it never worked, I just thought it did, but I mention this in case how I’m approaching this is the correct way and this indicates some kind of failure with the KVM that occurred over time.

2

I use an active HDMI-to-DP adapter from StarTech without issues: 1ft (30cm) HDMI to DisplayPort Adapter Cable, Active 4K 60Hz HDMI 2.0 to DP 1.2 Converter, HDR, USB

Its connected to a Thunderbolt 3 Dock, always worked with Windows and macOS devices.

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But is it routed through a KVM for you?

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yes generally an active adapter will work @Level1_Amber

a passive adapter will not work

1 Like
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Thank you for the ping. Club3D is pretty good if you want to give it a try. Also, can you link the specific adapters you tried and what cables you have? I see that your monitor is 3440 x 1440 at 144hz. I know 2560 x 1440 is good up to 144hz, but since this is wide screen maybe there’s a bandwidth problem?

This one is HDMI 2.1 → DP 1.4 for sure

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Thank you both for replying, but that’s why I posted. I’m on my second active adapter that is not outputting a signal. I wanted to understand if the two adapters I was using were expected to work, or if the StarTac or Club3D ones were expected to work. I just purchased the StarTac one, so if that one doesn’t work, does that mean there’s something else defective?

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Also, apologies, I’m trying to post links but I guess my rep isn’t high enough?

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do you have a link to them? you can’t go DP > HDMI > DP for example. And your active adapters generally must be usb powered because HDMI doesn’t work the same as DP for providing power.

So if your dock is hdmi its likely converting DP which is natively on USBC to hdmi. That hdmi can’t go back to DP. A display link adapter is “software” and natively hdmi because its a sort of usb-connected gpu? its weird… but that would work with an active hdmi to dp. those are slow/glacial/bad but… DisplayLink (haha).

You can use a usbc connection to DP as its dp signal type on the usbc cable straight into the kvm. and surface pros have their own dock style which mini dp to dp should work.

so not really enough info here to diagnose.

the framework is usbc to hdmi? if so its likely a DP to hdmi converter. Why would you not use USBC to DP “natively” in that case?

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Well, in this case, the Framework I’m using isn’t mine. It’s a friend of mine’s that I’m setting up. And the way I set up this particular connection, I thought HDMI was better as a “test-bench” setup. (Nearly) every laptop has HDMI, but it’s less common that something outside of a gaming desktop has DisplayPort.

Will try and clearly outline the wiring:

  • LG monitor connected to L1 KVM using Club3D cable
  • KVM connected to either of the two active adapters (BENFEI or Cable Matters)
  • Active Adapter to Framework via Monoprice HDMI cable

I’ve tried replacing the KVM-to-adapter cable with a fiber optic DP, but that didn’t work.

Again, apologies about not including links, I know that would help, I just keep getting an error that says I’m not allowed.

10

Okay, I leveled up. Links posted above.

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in general the benefi and cable matters style adapter SHOULD work.

I think the problem is that the laptop or the dock is not using “native” hdmi but usbc (display port signals) adapted to hdmi. Once you adapt, you can’t unadapt.
if you pop the usbc module out of the framework and try a usbc to dp cable, that’ll confirm. Or if you have another module position thats just usbc passthrough, I bet that works.

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Okay, I’ll give that a shot, and also try with this StarTac active cable/adapter I ordered. Thanks, Wendell!

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This is a good point I should post an fyi somewhere