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Sparking HDMI

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Sparking HDMI

I have a new TV which is connected to my A/V unit.

Last night I tried to watch some TV with the sound through the A/V but it failed with no sound.

I therefore removed the HDMI cable connecting the TV to the A/V and replaced it with one of a higher spec which worked fine.

 

However it was quite dark round the back of the A/V unit and as the shield of the plug touched the metalwork of the socket I noticed arcing, very small but clearly there.

Having been a welder for a number of years I'm quite used to arcing but I was surprised to see it in this situation.

Out of curiosity I measured the voltage between the socket and plug and my digital meter showed 95 volts AC Shocked

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Re: Sparking HDMI

In the instructions for my fairly new TV (last year) it stated to unplug everything from the mains before plugging in HDMI cables to avoid potential damage.
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Re: Sparking HDMI

Sounds like "floating voltages"

Basically the two items of gear aren't all earthed or none are. Voltage gets induced in the "chassis" of one, and when you touch the two together by a lead you get a tiny arc.

Once they're connected, the voltage will be equal, and no harm will be done. Hopefully.

As said above, any electronics gear, it's better to turn off before connecting leads.

 

If there's a ruddy great flash, then something's wrong!

But then it'd blow the fuses or bring the RCD out at the consumer unit.

 

  

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Re: Sparking HDMI

Wonder what caused the original cable to fail? At 95v I wouldn't be using it. But it surprising what you see in the dark sometimes. Maybe an iffy power supply or some stray currents. Who knows. I tend to take things apart, even more so when I sense that lovely electrical burning smell. Maybe I've been in the game too long and got addicted to it.

 

Something doesn't sound too good there (pardon the pun). Info Smiley

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Re: Sparking HDMI

@dvorak  Mine doesn't.

The only warning regarding connecting devices to the TV is to make sure the plugs are the correct way round and not upside down.

 

@idonno I believe the original cable didn't fully support ARC.

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Re: Sparking HDMI

Second post here

https://www.radioandtelly.co.uk/cgi-bin/forum/YaBB.pl?num=1269712967

 

I did think, as in the post after that, that if you'd have been using an analogue meter with lower impedance, you'd have probably read nothing.

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Re: Sparking HDMI

@Strat 

HDMI cables can carry up to 5 volts for power purposes but that sounds very much like an earth (ground) loop, which is very common between audio/hifi equipment connections. It's very rarely a "safety" problem because there is only a tiny amount of current flowing (ie hardly any power) and the spark is more like static. Are the two pieced of kit plugged into the same socket outlet (eg via an extension block)? If not, try doing that first so that they are both on the same earth connection. If no joy with that make sure that the HDMI cable is not running next to a mains cable or another signal cable, and report back! Haha.

In the vicinity of electric power wiring there will always be stray magnetic fields oscillating at the utility frequency, 50 or 60 hertz. These ambient magnetic fields passing through the ground loop will induce a current in the loop by electromagnetic induction. In effect, the ground loop acts as a single-turn secondary winding of a transformer, the primary being the summation of all current carrying conductors nearby. The amount of current induced will depend on the magnitude of nearby utility currents and their proximity. Since the wire ground loop usually has very low resistance, often below one ohm, even weak magnetic fields can induce significant currents.

https://en.wikipedia.org/wiki/Ground_loop_(electricity)

 

That's why HDMI cables shouldn't be hot-swapped as @dvorak has hinted at. It can cause damage to internal electronics from basically what the electronics thinks is a static discharge.

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Re: Sparking HDMI

@Minesapint 

That also backs up the earth loop theory!

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Re: Sparking HDMI

@nozzer Both items of kit are plugged into the same power block but as is normal these days, neither is earthed.

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Re: Sparking HDMI

@Strat 

That's the problem then. The chassis of the two bits of kit are at different potentials causing a spark. If I were you I would use the cable that did work, plugged in while everything is off, and just carry on regardless! You can get separate earthing equipment but it's not cheap and in this case not necessary I don't think. If you get to the point where you are hearing mains hum it's time do do something about it! Wink

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Re: Sparking HDMI

@Strat 

I've only skim-read the thread as I'm just rushing off to do something, so apologies if this has been suggested.

Is the mains lead at the back of the TV (or that of the AV receiver) connected by one of these 'Figure 8' plugs?

If so try reversing just one of them as, although it might sound daft, IME one of them being the 'wrong way round' can often cause what you are experiencing.

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Re: Sparking HDMI

@Strat 

My money would be on it being caused by a RFI filter capacitor discharging. The Y capacitors can float to half the supply voltage if the earth is removed. Not a problem at these levels but on seriously large  electronic products they can give a nasty bite unless discharge resistors are fitted.

In my misspent youth it was a common trick to charge a capacitor with a high dc voltage. It was then thrown at some unsuspecting person whilst shouting "catch". There was a lot of resultant swearing but no one got hurt!

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Re: Sparking HDMI

Interesting post.

I had a hdmi cable connected to tv & sound bar ........it worked fine.

For some daft reason I decided to use a better quality hdmi cable.....it did not work.....or at least no sound using it.

Switched back to the old hdmi cable and......that failed to work.

Extensive menu on the tv to select a range of things and whilst it showed the sound bar was connected in the menu and works ok through an alternative connection no way would it work via the hdmi cable.

I was using the correct hdmi cable...the op makes me wonder If I have shorted something out as I did not bother switching anything off ?

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Re: Sparking HDMI

I suspect that HDMI cables are designed so that the screen/earth connects before any of the pins do thus discharging any stray static charge that could cause problems with sensitive electronic components.

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Re: Sparking HDMI

@Strat 

They are. The outer casings should connect first before any of the pins so any unequal voltages will be equalised. Did you try it last night? Is it working ok? If so, leave it alone. That's the way it's designed.

As @Minesapint  said, using an analogue meter would probably have shown nothing (apart from an initial very short blip of the meter needle maybe) because the voltages would have been dissipated through the meter.