L1 Dual Monitor 2-Computer DP 1.4 KVM - PC1 display issues

I’ve had this KVM since August 2021 and have used it for roughly 14 hours daily (8 hours on PC2 for work, 6 hours on PC1 after) with no issues until very recently when PC1 began to stop working. Here are some details of my setup and the issue:

  • I am using all Club3D cables. The cables from the KVM to the monitor are 6ft, the cables from the KVM to PC1 are 3ft, and the cables from the KVM to PC2 are 6ft.
  • PC1 is connected via an RTX 3070 and I typically run both monitors at 4K@144Hz, PC2 is a laptop connected through an HP docking station, and due to limitations of the dock this runs both monitors at 1080p@120Hz.
  • I recently began to experience an issue only in Windows on PC1 where it would drop signal to one of the monitors. I could have it scan for input again at which point it would pick signal back up for about 7-10 seconds before dropping again. After a couple times, the monitor would lock up and I would have to unplug it to get it back to normal. On 2 occasions it caused the OSD on the monitor to be graphically glitchy rather than locking up.
  • This past weekend this behavior started happening on my primary OS as well (Solus; I only use Windows for VR or some misc utilities). The behavior is exactly the same–dropped signal, eventually locking up the monitor. Same monitor as in Windows. Part of me wondered if this was an Nvidia driver issue, as Solus updates occur near the end of the week and drivers would be behind Windows, but I can only reproduce through the KVM.
  • The OS will usually still detect the monitor and behave as though it’s still there (launches apps on that monitor, lets me move windows/cursor over to it) even though the monitor detects no signal, but it will eventually stop being detected by the OS. The monitor lock-up does not need to happen for the OS to stop detecting it, it seems completely random whether it will stop detecting it entirely or just stop sending a signal to the monitor.
  • After it started also happening in Linux, I started experiencing an issue where the KVM when set to PC1 would not wake the monitors on boot, and the monitors would not pick up signal from the KVM if the PC was already booting when I manually wake them. This is for both monitors. In order to get a signal, I must time when I power on my PC/wake my monitors such that the BIOS splash screen appears while the monitor is scanning for input. Otherwise, there is no way to ever get a signal. This is again only on PC1.
  • Power cycling the KVM alleviated the above issue but only for under a day.
  • The PC2 input on the KVM has to date continued to have zero issues.
  • I have tried running the computer attached to PC1 through the monitors directly (with lower-quality cables, at that) and that seems fine.

Wondering if: 1. this is something others have experienced; 2. there are any ideas for further troubleshooting; and 3. what do I do if I can somehow determine it’s definitely the KVM.

Thanks!

Nice, clear analysis & writeup of the issue.

You might try swapping the KVM ports used by the computers - PC1 plugged into the KVM where PC2 is now, and vice versa. Does the problem stay with the PC, stay with the KVM port, or mysteriously clear up?

You might also try running at 120 Hz instead of 144 Hz, to see whether the issue improves (because lower data rate may allow better meta-data transfer over DP). This would provide a little more information, and might be a long-term workaround.

Wishing you success.

Thank you for the reply. I will try swapping the inputs and see. I had avoided doing this up until now because my DP cables are zip-tied under the rear lip of my desk and I don’t think they have quite enough slack to swap without cutting a tie. But I agree that’s probably a good next step.

As for running with lower refresh rate, one of my troubleshooting steps this past Saturday night involved updating the firmware on my monitors, after which my PCs defaulted back to 60 Hz, and I didn’t notice for a couple hours. Unfortunately this remained an issue during that period.

You’ve probably thought of this, but… If your setup allows, it might be easier to physically move the PCs than to reroute the cables?

You might disable dsc in your monitors osd. It’ll sometimes use dsc independent of res/refresh. Nvidia has not been doing good dsc testing of late.

Try ddu and try the studio driver for your GPU.

I have now gone more than a day with the inputs swapped. I have had no issues on either input, other than the issue with boot not waking the monitors, which followed the PC having the problem and now occurs on PC2. I have had no other issues with the “problem” computer being on PC2, either in Solus or in Windows.

After work today I swapped them back again, so that the PC with the issue was back on PC1, and immediately had all the same issues again. So it appears to only happen when that specific machine is plugged into specifically the PC1 input. That suggests to me that something is funky with the KVM but I am not sure how to narrow that down.

I can’t turn off DSC on my monitors, as that option is not exposed. I also can’t force the monitors to use a lower DP version. They are locked into the highest version they can use with the input device (this is why I had to replace my previous KVM in the first place). Now that I mention that, I am pretty sure my work laptop’s docking station only supports up to DP 1.2. Could it be that something is broken with the PC1 input’s handling of DP 1.4 on one of the inputs?

Interesting. It could be emi/noise related or possibly something in the KVm.

Having the cables in slightly different places may affect interference they pick up, too. Spooky

I recently switched cables from the kvm to a problem monitor that was dropping out from 2m to 1m. Also did this on the PC side, but maybe less necessary. This pretty much fixed my monitors not connecting. I have had one time where it defaulted to a silly low resolution, but other than that it has been fine. I think if you can rearrange your setup to use a lower cable length, it would be beneficial.

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