Current through Composite Video Cables??

[swank121]

Didn't know exactly where to put this .. if I'm in the wrong forum, mods, let me know. I was playing around with the HDTV out of my 9800Pro the other day when I happened to grab one of the composite video cables and touch my case at the same time and .. ZAP!!! I got a strong and persistent shock, like you get from the mains. This has nothing to do with my computer, the current is coming from my 54" HDTV. The composite cables are plugged into the TV, and I can get shocked as many times as I like by holding any of the connectors at the other end and touching a ground. Is this normal? Why would there be current coming from my TV on the signal cables? If the TV is unplugged, I don't get any shock, so it couldn't be from any of the myriad of other power cords I have strung out across the floor. I know with component cables the TV can 'sense' if there is a connection .. perhaps this is why there is current. If so, wouldn't this be a "bad thing" for a video card? Thanks in advance for any replies.

 

[f95toli]

It is a common problem. Look it up in a home-cinema forum. It is probably due to the antenna cable-ground beeing different from your "normal" ground.

 

[Geniere]

I believe what you?re saying is the cable connected to the composite video input of your TV has voltage on the other end with respect to a ground.

If what F95toli says is correct, than test after removing your antenna input. In any case a ground is a ground and there must not be a difference in voltages from one ground point to another.

I made some measurements on a Sony video monitor that I have. I found no voltages above 1 volt AC or DC present on any of the composite inputs. I made measurements from ground to each jack, from jack to jack and from jack to chassis. My monitor has only a 2 wire line cord (no ground). If the frequency was beyond my meter?s range, it would not be measured properly. No antenna was connected to the monitor.

If voltage is present without the antenna connection, I would certainly be suspicious as it seems to me that there is a problem with your TV whether by design or by a fault. I suggest you contact the manufacturer and not connect it to your PC until you know what you?re confronting.

 

[Geniere]

Del du msg

 

[swank121]

Thanks for the replies. f95toli hit it right on the head .. as soon as I unplugged the coax cable from the back of my TV the phenomenon disappeared. Either my house isn't properly grounded or the ground at the cable station is different than the one here. My house is pretty old so it wouldn't surprise me if it's not grounded correctly. I'll leave the coax unplugged. I only get 10 channels anyway, so I won't be missing much. I'd rather play games and watch movies on the big screen anyways, and not risk frying my expensive video card. :beer:

 

[Peter]

Yep, that seems like your house wiring is screwed up (or rather not screwed up to ground correctly ).

I strongly suggest you fix that rather than ignoring it - that's accidents waiting to happen. What if the metal case of your computer, your toaster or your electric razor develops "voltage syndrome" next?

 

[f95toli]

As I have already written it is VERY common, my guess is that about 25-50% of the houses where I live have this problem. The reason is usually that the central antenna is not connected to ground where it enters the house (as it should be) and since there are always variations in the ground potential this means that the voltage can be rather large. It is normaly safe but you do risk destroying sensitiv electric equipment.

 

[Mday]

Originally posted by: f95toli
As I have already written it is VERY common, my guess is that about 25-50% of the houses where I live have this problem. The reason is usually that the central antenna is not connected to ground where it enters the house (as it should be) and since there are always variations in the ground potential this means that the voltage can be rather large. It is normaly safe but you do risk destroying sensitiv electric equipment.

more than you think. i would estimate 50-80% of homes. new housing must be grounded, old housing are not required to have it updated, unless doing renovations, etc. ground faults kill modern electronics.