HDMI and earthing problem

6 posts
by LarryIC » Fri Dec 14, 2012 1:37 pm
I have a weird problem with the RPi HDMI output. I'm connecting it to a monitor through an HDMI cable plus an HDMI-to-DVI adapter and I'm powering the board from an external wall adapter (5V 2A). It turns out that the monitor only works if i connect the RPi ground to the earth of my electrical system (or a metallic pipe, or anything else connected to earth). Until I was using the USB to power the RPi I did't experience this problem because apparently the PC USB ground is connected to the electrical system ground and therefore that already did the trick.
Has this any sense whatsoever? Maybe the HDMI adapter I'm using is missing some required pins?
Thank you for any thoughts.
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by boyoh » Fri Dec 14, 2012 4:05 pm
You must not mess about with the mains earthing bonding system.
What make and voltage is your Monitor, it must have a seperat
power supply, Do not power your Monitor from the same adapter
as the one used to power the RaspberryPI. Check your HDMI lead
or try a new one.

BoyOh ( Retired Electrical Electronic Technician )
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by RaTTuS » Fri Dec 14, 2012 4:10 pm
where in the world are you ?
what is the make and model of the adapter , monitor,
get a qualified electrician to look at your house wiring.
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by LarryIC » Fri Dec 14, 2012 5:01 pm
The electrical system is 220Vac 50 Hz (Italy). Here we have T-T networks:


There is nothing wrong about our electrical system (or at least I hope so :D ). The ground of PCs and other consumer devices is almost always connected to the mains earth, you can check by yourself with a tester. Obviously in the case of RPi powered by a wall plug adapter this isn't true.
Probably the display that I'm using (Hanns.G HH191) relies for some reason on the fact that the HDMI connector ground is connected to earth, which is normally true when it is connected to a PC but not true when connected to the RPi (unless the RPi is connected itself to a USB port of a PC or something else connected to earth, as I've written before).

The bottom line is that if someone has problems making RPi work with a certain display, he should also consider this.
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by terrycarlin » Fri Dec 14, 2012 9:09 pm
Could this be a cable problem? Cheap HDMI cables sometimes don't ground things properly.
If it ain't broke, take it apart and see how it works.
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by LarryIC » Mon Dec 17, 2012 5:52 pm
Yes, the blame goes most probably to the cable and/or the adapter. I will try something less cheap. Besides, this problem has already been reported:


For some reason I didn't find these threads the first time I looked. Sorry for the duplication :)

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