Oops: How to Toast any rPi with a 12v monitor

[/RaspberryPi]

If you're using a 12v HDMI display in your project, it's critical that the monitor be powered on before the Raspberry pi.
If the rPi is booted before the monitor has power, it sends 5v over the HDMI connection. The monitor senses the power, and tries to power up. This causes irreparable damage to the HDMI interface on a pi3 and pi4.
An electrical engineer friend of mine looked at the available diagrams of the rPi. They said there appears to be a voltage overload protection circuit that should reset after the device is powered back off, but that is not the case.
The rPi still computes and runs, but the HDMI output is trashed. It could still work over SSH/VNC or maybe the video ribbon cable, but no more HDMI fun. : (
(Anyone want to trade a toasted rPi 4 for a non-toasted older model lol?)

submitted by /u/just_gweat
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