The Tale of the Flickering Monitors

Like many software engineers and other professionals, I prefer having extra screen space when I'm working. At my desk in my home office, I have two external monitors that I use in addition to my laptop’s built-in screen. For the past few weeks, I’ve noticed that one or both would occasionally flicker. The offending screen would turn off for a second or two, then turn back on, with everything still on the screen where I had left it. An annoyance I could work around, but when I touched the docking station that my monitors were connected to, I noticed it was very hot.

Thinking the docking station might be overheating, I built a cardboard stand for ventilation. My mother-in-law happened to be around and suggested upgrading to a piece of plastic food packaging. That became version 2.0 — and it worked, at least for a few days. The docking station got a bit cooler and the flickering seemed to taper off.

Versions 1.0 and 2.0 of my homemade docking station stand

Yesterday, however, the flicker frequency suddenly picked up dramatically. The screens would blink multiple times per minute, interrupting my work and making them essentially unusable. The problem had to be re-addressed.

I had run into a similar issue about a year or two earlier. Somehow the mysterious flickering had been resolved, but I did not remember how - if it disappeared on it’s own, or if I found a fix, or what that fix might have been. Unfortunately, two weeks prior to the more recent incident, my group lost a large portion of our Teams chat history due to unrelated and unforeseen circumstances. I was on my own.

My first thought was to make sure this didn’t happen again next time. I started a new page in Notion so I could jot down whatever I was about to find out.

I thought this still might be an overheating problem, so I found a small fan and pointed it at the docking station. It made no difference. The flickering continued apace.

Then I got to work trying to isolate where the problem was really coming from. I swapped out my work laptop (system76, popos) for my personal one (lenovo, kubuntu), and the flicker continued. Whatever was happening probably did not have to do with the laptop’s hardware, since it persisted on two different machines. And if it was a software problem, it had to be something affecting both laptops.

I posted about the problem on my group’s Teams channel. Someone asked if I had done any system updates recently that might have unintentionally caused the problem. I hadn’t — certainly not anything that would have affected both computers. Still, I thought I’d try switching Linux kernels. (For context: in Linux, the kernel is the core of the operating system. Hardware-related bugs sometimes appear or disappear between versions, so trying a different kernel is a common troubleshooting step.) However, I knew that finding the right kernel might turn into a wild goose chase, assuming that was the problem at all. So before going down that path, I searched around and found a suggestion to tweak some Intel driver frame delivery settings (https://www.reddit.com/r/Ubuntu/comments/1cfzjpj/comment/lpc77o7/). Unfortunately, that didn’t help.

So I moved on to kernel hoping. I tried 5 different versions (6.0.19, 6.5.6, 6.8.12, 6.12.42, and 6.16.1), but the flickering persisted across all of them.

From there, I launched into a long back and forth with chatgpt. It suggested checking logs from various sources on my machine, using journalctl and dmesg. Nothing particularly insightful came from that. It then suggested updating the linux-firmware on my machine. I dutifully obliged. The flickering dutifully continued.

I then tried to clarify that chatgpt understood what I meant by “flickering,” realizing that the term could refer to different screen-related issues which might stem from different causes. It did understand. It just couldn’t figure out what to do about it.

At some point in all of these attempts, I noticed that the flickering followed an odd pattern. I normally stand when I work, and I have a desk treadmill that I use so I can walk at the same time. The flickering only happened when the treadmill was turned on. Strange, but consistent. The easy solution, without understanding what was happening, would be to stop using the treadmill. Of course, I didn’t want to do that, and I had been using the same treadmill and monitors for nearly four years with (almost) no issues. Why had the flickering suddenly jumped today?

I told chatgpt about the treadmill epiphany and it started talking about “electromagnetic noise” and “voltage dips.“ This was not my area of expertise, but I stuck around for the ride. It suggested rearranging the cables or moving the treadmill to another room (which would obviously defeat the purpose of a desk treadmill, but what can you expect from an LLM that doesn’t have to worry staying active during the workday?). I moved a bookcase to gain access to a separate outlet that I could plug the treadmill into. I threw in an extension cord and attached it to an outlet in the bathroom across the hall. Still no difference. The flickering continued.

Chatgpt recommended several other pieces of hardware I could buy that might (might) solve the problem — a more “well shielded” HDMI cable, an Uninterruptible Power Supply (or UPS), or a line conditioner — but I was hesitant to do any of these things not really knowing that they would solve the problem. It suggested “twist[ing] the cable on itself.” Easy enough, but also ineffective.

Finally, I went back to Google and updated my search: “monitor flickering when treadmill on“. The first result led me to a reddit user with the same brand of treadmill, complaining that their screen flickers when the treadmill turns on:

I just bought a walking pad so that I can work while getting my steps in. I was super excited to get started, only to realize shortly after that walking on the treadmill while using the computer causes my monitors to flicker…

Update: I have found a silly, but useful solution to this problem. I figured that the issue was caused by static electricity. I googled how to get rid of static electricity, and it said to create more humidity in the room. I have a spray bottle of water, and I just spray it on the track of the treadmill. Don’t spray too much so that you’re slipping and sliding, but just enough that it is a tiny little bit wet. This is seem to solve the problem for me. I’ll probably get a humidifier.

— https://www.reddit.com/r/Monitors/comments/10jfbfh/monitors_flicker_while_using_walking_pad/

And then it hit me.

A few days earlier, I had discovered some mold growing in my office. Among the measures that I took to address that, I put a *de*humidifier in the office. By now, the dehumidifier had been sitting there for just about 24 hours and, together with the treadmill, created the perfect atmosphere for screen flickering. I had found the answer.

I found a spray bottle, and sprayed a bit of water on the treadmill. The flickering stopped.

And with that, I was back to my regularly scheduled programming (pun very much intended).