On 06 Jan 2021 at 10:31:01 GMT, Martin Gregorie 
wrote:

> On Wed, 06 Jan 2021 09:44:02 +0000, Mike wrote:
>
>>  In article ,
>>  Andy Burns   wrote:
>>> Tim Streater wrote:
>>
>>>>  The Pi carried on being powered.
>>
>>> Unless a 4B is different to any other rPi, they never turn off, they
>>> just halt.
>>
>>  But, from the original post, which you snipped :-
>>
>>>  A bit later I shut it down, **and then turned off the Pi power
>>>  supply.**
>>>  The Pi carried on being powered.
>>
>>  Are you saying the Pi 4B is a stealth free-energy device? ;)
>
> Its not. This just shows that, if there are common positive and ground
> rails on the Pi's PCB that are connected to ALL sockets capable of
> accepting a connection from an externally powered peripheral device,
> which AFAIK is the case for all Pi models, then a Pi will remain active
> as long as external device with a power source providing enough current
> to keep the RPi alive is connected to it.
>
> It also means that you can destroy a Pi by connecting it to anything
> which requires more than 5v to operate and that has its positive and
> ground rails connected to the plug it uses to talk to the Pi.

OK. So what device is providing the power to the HDMI cables, and why? In my
setup I have a Dell display connected via its DVI (?) socket and an adapter to
a small HDMI switcher that can route the display either to my Mac Mini or to
the Pi.

I did notice that, after disconnecting the HDMI from the Pi, and reconnecting
it (all this with the Pi's power adapter unplugged from the mains), the Pi did
not power up again. So whatever is on  teh HDMI is not a strong power source.

--
Tim

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