KVM PC1 doesn't work with Macs, but PC2 does?

Hardware
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1

Hello everyone,

I’m trying to figure out why my setup doesn’t work on my KVM’s PC1 ports (any of them), but it does work on the PC2 ports. When the setup works, my monitor connects perfectly. When the setup fails, it connects for ~3 seconds, disconnects for ~3 seconds, over and over. The display goes black and the System Preferences Display pane shows the monitor coming and going.

Through troubleshooting I was able to determine that all the PC1 ports on the KVM (Quad Monitor, 2 PC KVM) don’t work with any MacBooks, but all the PC2 ports do work. ALSO, the PC1 ports work fine if I put a Thunderbolt 4 dock between the KVM and the MacBook.

The following chart shows what does/doesn’t work. Note that I have 3 of these monitors, lots of spare cables, and two different MacBooks (Intel & M2) and the only thing that works for all that hardware is to either use the PC2 ports or the Thunderbolt dock. Can anyone guess what might be going on here? Does this mean the KVM is faulty? (Also, I didn’t capture this in the chart, but the PC1 ports and all configurations work just fine with my PC.)

KVM-Troubleshooting-2023-02-19.excalidraw
KVM-Troubleshooting-2023-02-19.excalidraw1920×2110 184 KB

2

And in case anyone is curious, the reason the Thunderbolt dock is not a solution to my problem:

I’m trying to drive 3 monitors and the dock can only drive 2 monitors. I have to plug the 3rd monitor directly from the KVM into the MacBook and go around the dock.

3

Have you tried swapping the cables between port 1 and port 2 to make sure 1 of them isn’t faulty? and/or a fake Club 3D cable (we’ve had that happen).

If your issue persists, try emailing:

wendell at level1techs dot com

An RMA might be in order.

4

Hey all, @wendell was kind enough to consult with me over email and I’m reporting back findings here. It looks the Moshi DisplayPort/usbc cable is working perfectly where the Club3D wasn’t cutting it. So here are my findings for getting the L1 KVM to work with 3 displays on a MacBook 2023 M2 Max (the only Apple Silicon MacBook that works with 3-4 displays):

Displays 1-2 (through dock):

28MQ780-B     => 
L1 KVM        => 
TBT4-UDZ Dock => 
MacBook

Displays 1-2 going through the dock don’t seem to be as picky about cables. I used a mix of Club3D cables and whatever came with hardware.

Display 3 (direct to laptop):

28MQ780-B => (via FIBBR 6.6FT fiber optic DisplayPort Cable) 
L1 KVM    => (via Moshi DisplayPort to USB-C Cable)
MacBook

After 1.5 days of testing I’ve had no dropouts, the display has survived sleep/wakeup ~5 times, and I have no visible signal noise. Seems to be working great.

Note that I went back and replaced the FIBBR cable with my old DisplayPort cable and that didn’t work, so it’s BOTH the FIBBR and Moshi cables that are necessary for this to work for me for whatever reason.

5

Hey Altano,

Is your setup still operational normally with the l1 kvm? I also would like to switch between a gaming pc and a M2 Max macbook pro such as yours and was wondering if your setup was still a reliable option.

Thanks!