/Raspberry Pi 4 WiFi stops working at 2560 x 1440 screen resolution

Raspberry Pi 4 WiFi stops working at 2560 x 1440 screen resolution

This is part of a series of post on the design and technical steps of creating
Himblick, a digital signage box based on the Raspberry Pi 4.

One full day of crazy debugging, and the result is that if the Raspberry Pi 4
outputs HDMI at a resolution of 2560×1440, the WiFi stops working.

Any lower resolution we tried, from 2048×1080 down, does not show this problem.

We did not try any resolution above 2560×1440, for lack of a monitor that would
do it.

One of the micro HDMI cables that we used

We reproduced this:

  • on both microHDMI outputs
  • with two different cables: one with a microHDMI to HDMI dongle adapter; one
    direct microHDMI to HDMI. The latter is the one I bought in the
    Raspberry Pi Store in Cambridge
    together with one of the Pi 4 units.
  • with three different RaspberryPi units
  • with 4 different power supplies: one rated at 2A, one rated at 3A, one rated
    at 3A bought in the Raspberry Pi shop in Cambridge, and a laptop USB-C
  • with stock Raspbian Buster Lite
  • with stock Raspbian Buster
  • killing every process in the system, starting the network manually with
    wpa_supplicant and dhclient, and starting X manually with sudo X
  • with two different SD cards
  • connected to an AP some meters away, and connected to a phone hotspot next to
    the Raspberry PI

At the bottom of this forum thread
(guestxyz dated Aug 07) someone mentioned screen resolution, which is what
finally prompted us to try that. Thanks, guestxyz!

After confirming what the trigger was that caused the problem and chatting
about it on IRC, olasd found this forum

where more people are experiencing similar issues.

Further things left to try after chatting about it on IRC:

  • whether disconnecting the HDMI cable from the Pi end (with X still started
    at high resolution and everything) make the WiFi work again
  • switching the monitor to another input while the Pi is at 2560×1440
  • letting the monitor go into power saving mode while the Pi is at 2560×1440
  • cable chokes


This post seem to have become quite popular, so to be clear, the intention is to
document the issue that we spent a whole day chasing so that others won’t have

It’s been fantastic to see how this has made the rounds and resulted in actual
RF measurements being made, and better pinpointing of the issue than we could
ever have achieved.

I greatly admire Raspberry Pi’s work. Thanks to them we get to have an
affordable standard platform with a wide use base, which over time gets
extremely well known, and as such can be a very well mapped ground to build on.

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