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Just doing some testing for a project. The project involves two SBCs right now(one is the Raspberry Pi 4b). I have one TV handy so I had the other SBC connected initially. For reasons pertaining to the project, I turned on both SBC's simultaneously. The Pi started unplugged to any HDMI port.

Later I prompted a proper shutdown on the connected SBC and then connected the Raspberry Pi's HDMI to the TV. I intended to initiate a shutdown on the Pi as well. However, I could not get the image to appear. Only stating "no signal". I tried other HDMI ports on the TV, the other microHDMI port on the PI, I borrowed someone else's TV and tried it...same problem. Curiously, when I remove the cord the TV displays "check signal cable", and when I plugged back in I get "no signal". Also I clicked my mouse/keyboard just to make sure the Pi wasn't in some "screen saver"/"sleep mode" as they do when you leave them idling temporarily.

Knowing no other way I unplugged the Pi to shut it down despite knowing that's risky. When I turned the Pi back on, the desktop page displayed normally.

I continued testing and forgot my earlier mistake. Turned off SBC 1, connected the HDMI to the Pi and same problem. I was forced to shutdown the Pi improperly a second time.

This leads me to my questions about the Pi:

When starting up, if the Pi does not sense a HDMI connection does it change a setting or something? Thus making a connection later not work?

If this happens again, is there a way to turn the Pi off correctly without a display?

Thanks everyone

gumby4231
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1 Answers1

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There are many ways of safely turning the Pi off without a display.

You can still ssh and shutdown.

I use dtoverlay=gpio-shutdown,gpio_pin=21 and when BCM 21 (pin 40) is connected to Gnd the Pi shuts down. See https://raspberrypi.stackexchange.com/a/77918/8697 for detailed description.

NOTE that the risk of powering the Pi off it greatly exaggerated. It CAN cause problems if power is removed when the Pi busy (especially during an upgrade) but if inactive is unlikely to cause problems. The power has failed on my Pi hundreds of times over the years - they just reboot when power is restored.

Milliways
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