Question No video after switching with KVM

Jun 24, 2022
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I have two computers, a desktop PC that I built and a Beelink U59 mini PC. I bought a Ugreen CM200 2-port HDMI KVM switch so I could share my monitor, keyboard and mouse between the computers. Everyhing worked great for several weeks, then one day the desktop PC started losing video after I'd switched the KVM to the Beelink and back again. It occasionally works, maybe once, but usually fails. I have to press the reset button on the desktop and reboot to get video back. If I boot the desktop into the BIOS screen I can switch back and forth all day long, just not after I've booted into the OS (currently MX Linux 21.1 AHS based on Debian Bullseye., kernel 5.17. Until a few days ago it as MX-19.4) based on Buster with kernel 5.10 Also I have an encrypted system and it also fails if I leave the desktop at the decryption passphrase prompt then switch to the Beelink and back. The Beelink never has any video issues. I have tried both updating and downgrading the BIOS version and the Linux kernel on the desktop, and tried two different HMDI cables between the desktop PC and the KVM switch. I'm wondering if it could be a PSU issue? Not enough power to the GPU? (The desktop PC works fine when connected directly to the monitor, no video issues at all.) Maybe it's that on video port on the KVM switch that's acting up? (Yet there's no problem with video if I'm sitting on the BIOS status screen.) Maybe PCI-E power since the NVMe drive and GPU are sharing the PCI-E bus? Maybe I need a different video card that uses a power cable rather than or in addition to bus power? But why would I lose video only after switching the KVM away and back? When I was buying parts for the build all the power supply calculators recommended a PSU of around 380 watts or so, so I should think my 550W PSU has plenty of power for this system. The voltage values look OK when I check them in the BIOS's monitor. Unfortunately the sensor module in Debian doesn't show system voltages while the OS is running, just various temperatures and "amdgpu/in0" (1.10V.)

What do you think? Do I need a more powerful PSU? Different graphic card? Different KVM switch? HDMI cable quality?

Desktop specs:
Monitor: ViewSonic XG2705 Elite 27" 1920x1080 FHD connected via HDMI with 144Hz refresh rate
GPU: Biostar Radeon RX 560 4GB GDDR5 with two fans, single PCI-E slot, no external power cable
Motherboard: AsusTUF B450M PRO GAMING
CPU: Ryzen 7 3700X 8 core 16 thread
PSU: CoolerMaster E550 80+ Gold fully modular, 550W
Case: Thermaltake Versa H25
Fans: two Arctic 120mm intake fans, one Thermaltake 120mm exhaust fan that came with the case
CPU cooler: Snowman M-T6, 6 heatpipes, two 120mm fans
RAM: two PNY 16GB DDR4 2666 modules with RGB lighting (that I didn't want)
Drives: one PNY XLR8 CS3030 500GB NVMe SSD, one Seagate ST4000DM004-2CV104 4GB 7200RPM 3.5" HDD
USB devices: One USB2 cable that goes to the KVM switch
 
Jun 24, 2022
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Ain't it always the way? After I posted I may have partially solved it, though I don't understand why. I checked my display settings in Linux and found that the refresh was 60Hz not 144HHHz like I'd specified. I also disabled detection of new displays when they're connected. I saved those settings as a display profile in Xfce and now everything's working, except if I switch to the Beelink and back at the encryption password screen, which is of course before I've logged in and my 144Hzdisplay profile is loaded. I don't understand what the refresh rate has to do with it. The Beelink's integrated Intel GPU in its Jasper Lake N5095 CPU is 60Hz and it has no problems. I take it back: the Beelink mini's using 144Hz. So apparently my monitor and my KVM switch will only cooperate at a 144Hz refresh rate, not at the standard 60Hz. Weird. Unless it was caused by having different refresh rates on the two computers and setting the Beelink to 60Hz would have also fixed it?
 
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