My monitor, an old Toshiba 47wlg66, will display what my boards output (whether it's my old raspberry pi 1 A or new raspberry pi 4 B) only if it was powered first. Otherwise it will remain black..

It is troublesome because I power the 2 at the same time, and the PIs must be quicker to send their first signal because in that case the screen remains black and I need to power off and on the PI for the monitor to recognize the signal.

I usually use dietpi, but have seen this behaviour with raspbian as well. Is there a way to fix that, or at least some kind of signal I could send from a script that would tell the monitor to start listening as it does whilst booting?

  • Leave it all powered on! – Dougie Jun 29 '20 at 22:19
  • @Dougie that won't do. People can mess with it, and I want a real fix.. – Shautieh Jul 4 '20 at 23:04

You need to force HDMI output in /boot/config.txt (earlier models defaulted to composite, the Pi4 does nothing).

    # uncomment if hdmi display is not detected and composite is being output

This requires a default resolution to be set in raspi-config (at least on the Pi4 - earlier models defaulted to VGA resolution).

It is also possible to set resolution manually, but in raspi-config it is easier to select a resolution supported by your monitor.

Mine is (this selects a different resolution if the wide screen Acer is detected) -

#DVI DMT (35) RGB full 5:4, 1280x1024 @ 60.00Hz
#DVI DMT (82) RGB full 16:9, 1920x1080 @ 60.00Hz

NOTE don't just blindly copy the values above - set defaults which are supported by your monitor, so it will work if the monitor is connected.

  • When trying to get the right resolution with the pi4, I tried setting those hdmi groups with no great success. Specifying the framebuffer_[width|height] options did do the trick along with overscan_*. I'll try again setting the hdmi_group and the force hotplug next time I am in front of the beast! – Shautieh Jul 4 '20 at 23:12

Is it because the Pi is defaulting to a low resolution? You can try setting the default resolution (within the configuration) to match the resolution of your monitor. I forget what the default resolution is but it is much less than monitors typically are - it's probably set to target the small touchscreens.

  • I don't think it's related, but I set a resolution already in my config.txt. – Shautieh Jul 4 '20 at 23:06

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