External Displays black out periodically at 4k 120Hz

Framework Laptop 13 Linux
1
  • Fedora 40 KDE Spin
  • Framework 13 Ryzen 7 7840U 2.8K; 2x16 GB RAM

I have 2 4k 120Hz displays at my desk that I want to use with my Framework 13, but regardless of whether I have one connected or both, I get periodic (~5-30 second interval) display blanking that lasts ~1 second before recovering, which makes the setup virtually unusable.

I’ve used these monitors previously with full-res/full-rate input so I know it’s not the cables or the monitor. I’ve tried connecting via DisplayPort expansion card, USB-C expansion card (USB-C to DisplayPort cable), and connecting USB-C to DisplayPort cable directly to the mainboard. The problem happens regardless of which of the 3 ports with display output I connect to.

It seems like there is no blanking if I lower the refresh rate to 60 Hz, though that defeats the purpose of having a high refresh rate monitor.

2

I unplugged for a while, upped the iGPU RAM to Gaming, then hooked back up & got different behavior; this time only one monitor was having blanking, but a lot more frequently. Unplugging and replugging a couple times and neither monitor is blanking anymore.

Opened the lid and it blanked again, this time with the monitor claiming the input signal was an unsupported resolution (briefly) before going blinking a couple more times then going back to being stable. I’m beginning to suspect my setup is having borderline signal integrity issues.

3

Okay, most likely it’s my cable setup. Have not had a blanking for over an hour and 2 replugs of the setup.