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My touchscreen that I've attached directly to the Pi shows a black screen with a blinking cursor on boot up. However, if I attach a mini-HDMI to DVI cable to the Pi while it is off and then boot it on, it proceeds to the desktop as desired.

The monitor the DVI side is connected to does not have to be powered for this to work, but the cable must be connected to it. The cable can be removed after boot and nothing happens, though it must be reinserted if rebooted. When the Pi is booted up with the cable connected and the monitor powered, the boot screen shows first on the touchscreen, then moves to the external monitor.

I've searched the wiki and the boot issues sticky and found unsatisfactory answers. I will reflash my SD card as a last measure, but I feel like there is a simpler solution given that it works under certain conditions.

Pi with cable unplugged Pi with cable plugged Powered external monitor

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  • DO NOT post illegible pictures - post TEXT.
    – Milliways
    Jul 4 at 0:24

1 Answer 1

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The Pi4 (in contrast to earlier models) has NO video output unless a monitor is detected. See https://www.raspberrypi.com/documentation/computers/config_txt.html#hdmi-mode

The OS CAN be forced to set resolution even if no monitor is detected.

Setting hdmi_force_hotplug to 1 pretends that the HDMI hotplug signal is asserted, so it appears that a HDMI display is attached. In other words, HDMI output mode will be used, even if no HDMI monitor is detected.

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  • When I first set the screen up, I followed this guide and in /boot/config.txt I added dtoverlay=waveshare35a. On your recommendation I added hdmi_force_hotplug=1 to config.txt and that allowed it to boot up into the desktop with no HDMI cable connected. Jul 4 at 1:33
  • Curious about a detail that might be assumed knowledge in the answer: Does this mean the touchscreen used in the question is not being detected as an HDMI monitor? (e.g. no EDID provided?)
    – Gertlex
    Jul 4 at 6:02

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