Return to

The Level1Techs KVM (Keyboard, Video Mouse) Switch - 4k/60hz monitor & USB Switchbox | Level One Techs


The only known good cables are the ones in the kit. I believe Wendell will sell you some, but I don’t want to put words in his mouth.

Your problem is almost certainly a display port 1.2 issue but it’s also possibly the cables. I’ve had issues with display port protocols over 1.2.

Ah, it could also be the thunderbolt adapter causing trouble.


I mentioned in my post that I tried the cables from here. I ordered two sets. I get the same results with them as with the other cables I have. And everything’s working fine on Windows, as noted.

I do have an update, though… I swapped the cables between the “top” and “bottom” ports on the KVM (I had previously only been switching to different numbered ports, but not changing which monitor went into the top and which went into the bottom), and now I have the reverse behavior. The Acer is detected, but the Dell isn’t.

It could be the Thunderbolt adapter, but the standalone DisplayPort -> Thunderbolt cables I have exhibit exactly the same issues.

What do you mean by DisplayPort 1.2 issue?


Sorry, I’m not 100% right now, I did notice that you’d tried them though.

This kvm technically doesn’t support over 1.2. After manually switching my monitors to disable 1.2a, in favor of 1.2, it worked fine. At least, that’s my experience.

In regards to the thunderbolt adapter, it is possible. I don’t really know what to say there, since I don’t actually have hardware to test it with. It’s possible, and we have seen problems with them before.


I see. Looking into it, it seems like both monitors are DisplayPort 1.2.

By disconnecting and reconnecting cables and switching back and forth a few times, I was able to get both monitors displaying with the Mac… but unfortunately, switching to the Windows PC and then back to the Mac brought me back to square one, with only one of the monitors working.

I’ve also noticed occasional noise on the display on the Mac, and changing refresh rates a few times will usually make it stop. I’m not sure if that’s of any consequence here, though.

This is such a bummer after putting so much money into this.


I recently got an LG 34GK950F monitor, which has DisplayPort 1.4. It’s got an option to force 1.2 mode in the OSD though. I enabled it and the KVM still won’t work properly with it for some reason :frowning:

Just get a black screen when connecting to my Linux/macOS systems through the KVM. Oddly though, it works in Windows. Using a Vega on the Windows side while the Linux has a RX 550 and macOS has a RX 570.

Anything I could try to possibly fix this? I tried shorter cables, using the ones in the kit actually. Not sure why it works in Windows and not any of the other OSes…

In Windows, I can even get it to work in DisplayPort 1.4 mode, at 144Hz, albeit with flickering every now and then so it really doesn’t work properly but found that interesting.

Had it all working on my older 38UC99 ([email protected]) monitor which should be around the same bandwidth requirements as this in DP 1.2 mode.

At least this monitor can do 85 Hz over HDMI so using the secondary inputs has been ok… would like to get it working through the KVM though.


The occasional flicker may mean one of the devices are not quite outputting enough signal. Is neither monitor widescreen? If 16:9 aspect ratios I can let you borrow a display port repeater which helps with diagnostics and may resolve the issue. A lot of TB dp adapters barely have enough signal for 3 feet of cable…

Some Linux AMD drivers don’t properly try to retrain the display on error, and Macs almost always don’t do that. So there is this handshake where the device is supposed to try 3 times and for some reason some devices only try once.

Also, if there are Nvidia graphics cards in the mix here, make sure they have the firmware update installed. Without the dp firmware update their dp1.2 is slighlty out of Spec. I can work with you on a return if nothing else but I like to know as much about the edge cases as possible in case it’s something I can fix.


Both are 16:9. The Windows machine has an nVidia card, but the KVM seems to work fine with it. Would that still possibly affect other machines on the KVM? The Mac has integrated Intel graphics. Regardless, I can try to do the firmware update and see what happens.


Usually the Intel igpu graphics are the most solid esp. on the nucs. That’s interesting. Pm me your order # and address and I’ll mail you a repeater to try after you update the Nvidia firmware


Well, good news is that updating the firmware on the 1080 Ti seems to have removed all of the weird flickering issues I was having when trying to use gsync with both monitors set to 144hz, so thanks for that. No residual effects with the Mac, however. Still only able to get one display working at a time reliably with it. I’ll toss you that PM.

EDIT: I can’t seem to figure out how to PM. Maybe I’m not allowed since my account is so new?


@wendell I received the repeater today. Unfortunately, I’ve tried it in various configurations:

  • between one monitor and the switch
  • between the other monitor and the switch
  • between the Mac and the top port of the switch, with the Mac side using the dual port DP to TB3 hub
  • between the Mac and the top port of the switch, with the Mac side using the direct DP->TB3 cable
  • between the Mac and the bottom port of the switch, with the Mac side using the dual port DP to TB3 hub
  • between the Mac and the bottom port of the switch, with the Mac side using the direct DP->TB3 cable

In scenario 3, I managed to get output on both monitors, and although the Mac did not detect the resolutions or device name properly, I was able to manually set the resolution and everything was good. Then I switched over to the Windows machine and back to the Mac, which left me with both monitors black and neither would turn on until a reboot, which left me back where I started with only the one monitor sans repeater working. And I haven’t been able to recreate that success since.

I’m out of ideas, personally. This past week, I’ve been using HDMI out on the Mac and running that to the secondary input on one of my monitors, which has enabled me to do my work… but I’d really rather have both monitors going through the KVM. The KVM has been great, otherwise – it’s working really well with my keyboards and on my Windows machine.


I wonder why Windows seems to be less picky w/ the KVM.

I still haven’t been able to get my 34GK950F to work with it, on Linux or Mac. The monitor also has a setting to go down to DisplayPort 1.1 which I tried, still get a black screen. It even works when using the DisplayPort 1.4 mode on Windows, as long as I limit the refresh rate to 120 Hz (144 Hz gives flickering, expected though).


In a working config, hit the edid copy button then switch the output to port 2. That should maintain the edid across mode switches. Though it’s very odd of both monitors don’t come back from switching in this scenario? More data might help with a firmware update


When you did dp1.1 did you power cycle literally everything? Kvm, PC, etc?


Tried it again, this time power cycling the monitor and it worked :slight_smile: Thanks. Also tried it under DP 1.2 @120Hz and still had no issues.


You probably also need to totally power cycle literally everything for each combo you try … pc, docks, kvm. Helps if everything is on the same power strip. Power cycle the Mac too. Drivers on Mac and Linux especially try to remember stuff which ends badly


Okay, I’m hoping Level1 can fulfill a need I currently need:

I need a Displayport 1.2a MST HUB/SST splitter combo that can manage EDIDs and can switch between being a MST HUB and a SST Splitter, that can also support HDCP 2.2.

This product doesn’t exist yet. The closest one by ATEN only supports HDCP 1.3.

Most 1x4 splitters and cheapo 1x2 splitters have no EDID management, so sources can get confused on which EDID to choose. Ones that have proper management don’t support HDCP 2.2.


If you find an answer please let me know, I would like something like this too.


I’ve been thinking about it, and the Level1Techs Displayport MST hub/SST splitter would work something like this:

Input: DisplayPort


In MST hub mode: 2x DisplayPort outputs with EDID muxing for MST, and 1x active DisplayPort to HDMI conversion to HDMI 2.0 with 2 way EDID.

In SST splitter mode: 2x DisplayPort outputs, with output 1 being the EDID sent back through the input, and a switch for the 2nd DisplayPort output between DP output 2, and HDMI output 1. If the 2nd DP output is active, the HDMI is inactive. If the 2nd DP’s signal is then routed to the DP to HDMI converter chip on the hub/splitter, the DP output 2 is disabled, and the active DisplayPort to HDMI conversion is done to the HDMI output.

Best of both worlds, a 2x DP, 1x HDMI MST hub, and a SST DP in to 2x DP or 1x DP and 1x HDMI split output. I can tell you right now this will help a ton of high frame rate people for streaming or recording (Twitch supports 720p at 100fps)


Wendell is there a firmware update for the dual port? I am having issues running 34" dell and 24" the panel flickers on the 2nd port or is black. Using vesa certified 1.4 DP cables

Have issues on both TB dock with dual DP and desktop running a gtx 1060

Still need to check DP settings on monitor, but figured adding firmware update would be worth wile


Did you get the Nvidia DP firmware update installed?