I use a three-monitor setup with a LevelOneTechs 2-in-3-out KVM. I have my personal desktop, which is a Minisforum UM700 running standard Manjaro Plasma (Plasma vs. 5.27.9); and my work laptop, which is a MacBook M1 Pro. The UM700 supports triple-monitor functionality in the form of one DP connection, one HDMI connection, and one USB-C connection. Since the KVM only accepts DP connections in or out, I have the appropriate converter cables where required.
For about 9 weeks, this setup has run without (major) issue. The worst quirk that manifested was that if the desktop went to sleep and then woke back up, sometimes (but not always), the monitor designated as the ‘primary’ would change, so the toolbar would shift over there. Nothing worth fretting about. However, this past Wednesday (8th November) I experienced a short-lived issue where only two of the monitors were receiving signal from the desktop, and the monitor arrangement was ‘flickering’ such that the tool bar was moving back and forth between the monitors every few seconds. Here’s how my troubleshooting went:
- Unplugged and replugged the cable that drives the monitor that wasn’t working: this was the USB-C-to-DP cable. Replugging it in didn’t do anything, and the connection didn’t feel in any way loose. However, while it was unplugged, the screen flickering stopped, and the toolbar stayed on one monitor the whole time.
- Swapped in a different USB-C-to-DP cable. This didn’t change anything, so I wondered if maybe the output port was the problem.
- Switched KVM state to my work laptop. All three monitors received signal as expected both with the USB-C-to-DP cable it was already using, and with the one I have been using for my desktop when I tried swapping that in.
- Switched KVM state back to my desktop, replugged everything like before, and rebooted. This didn’t have any observable effect the first time.
- Unplugged and replugged the KVM itself. No effect.
- Rebooted the desktop again. This time I waited a bit on the login screen–not only did the monitor that wasn’t coming on before come on, it wasn’t even the last one to come on. I logged in and the monitor immediately went dark again, and the flickering resumed.
- Stepped away for a moment, came back and the problem was gone.
Between then and roughly 45 minutes ago, I had not encountered the issue again. All through this morning and early afternoon, all three monitors were working exactly as expected. I spend the evening out for a few hours, come back and find that the problem has returned, and responds/fails to respond to troubleshooting in the same way. I lingered on the login screen for several minutes this time and the monitor in question never went dark, but the instant I logged in, it did and the flickering resumed.
What ultimately did the trick was unplugging all of the cables that run from my desktop to the KVM input ports, and replugging them in, but ONLY if the monitor that was going dark was not the last one I plugged in. The pairing of cables to ports didn’t have any effect, only the order in which cables were connected. I suppose there’s a possibility that it’s a hardware issue, but it’s so quirky that I wanted to explore the possibility that it’s something with Plasma, since it does seem that people sometimes have issues with multi-monitor setups on it.
Please let me know what additional information, if any, I can provide. Thanks in advance.