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50V AC coming from RF connector

Basically is it normal for TVs to output 50V AC from core and sheild to ground only when the TV is turned on?

Here is my long and drawn out story but I hope someone can help me.

Cable company shows up at house to try and figure out what is going on with the cable in my area. When they guy was disconnecting the cable from the main splitter in the house he said he felt a current over the line and then proceded to test the line he said he was getting 65V AC from the core and the sheild. He said I would need an electrician to test the grounds and fix it. I personally wasn't home when he was there this is just what he said when I called him.

Electricians came and tested all the grounds and all were fine. We hooked up the TVs 1 at a time and each TV was outputing around 50V from the core to ground and from sheild to ground. So to elimiate cable issues I tested the RF connector on the TVs directly. I tried from the inside of RF connector to ground in plug and got about 50V AC then from the outside of RF connector got 50V AC as well. I called back eletricians and told him this was happening and he said this was normal (thats how tv's work) and that cable guy should have know this.

I tried that same test with a TV from my buddy's house at my house and at his house so I assume this is normal for cheaper TVs, since neither of our big screen didn't do i.

Called back cable guy and he stood by what he said that, that isn't normal can if he came back to check and was still outputting voltage he would disconnect it all.

Any help would be great

Reply to
flounder_1
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I don't know the voltage but ever since I was a youth and tinkered with tv's and videos, I have always had a tingle off any tv I've had and also at every house I've had.

I used to work in a tv shop selling tv's too and they all tingled. Someone said it was the static building up from the screen but I guess it could just be the way they work.

Reply to
Dave

They're not broken, the AC voltage is due to the mains filter as I explained - the more appliances you connect together (VCRs set top boxes DVDs etc) the more current you can draw. If the cable company is refusing to connect their box to TVs in this situation its hard to see how they stay in business!

Reply to
ian field

It's completely normal. Many TVs (particularly cheaper ones) have a hot chassis. This means that the chassis is connected to the power line and has voltage on it compared to ground. The tuner input is isolated from the hot chassis with a network of capacitors and resistors that block the line voltage, but pass RF. If you measure the voltage with a typical volt meter it will show a voltage, due to the meters high input impedance. As soon as you ground the RF connector the voltage will disappear. If this isolation network failed, you'd know it when you connected the cable (loud bang, lots of sparks, blown fuses...). Andy Cuffe

snipped-for-privacy@gmail.com

Reply to
Andy Cuffe

I assumed this was all normal and the cable guy didn't know what he was talking about.

Should you be able to feel this voltage across then end of the cable? With 2 of 3 TVs you can feel it when you put your finger over the end of the cable.

When I ground the splitter where the offending TVs are connected and then disconnect the input from cable company and test that input to ground I only get 0.1V which I assume is an acceptable level for their equipment to deal with.

Thanks alot for you help. Just have to convince cable guy it is suppost to do that.

Reply to
flounder_1

You need to ground the shield of the cable connector on the tv set to a real ground, fpor as long as the cacle guy hangs around. Previous posters about hot cheap chassis are 100% correct.

H. R. Hofmann

Reply to
hrhofmann

Thanks again guys. Just called cable company and I guess guy was at my house today and checked it out and all is good. Guess he didn't want to call me and admit he was wrong.

Reply to
flounder_1

They are incompetent.

Very little CURRENT flows from such a connection. It's the CURRENT that's dangerous and in this case the current is limnited to a safe level.

It's the cable company that's out to lunch.

Graham

Reply to
Eeyore

Who ever said those sorts of people were all "professionals"? A majority have basic experience at best. A "neighbor" had RF interference once - on their phone - from my "Ham" station. The "phone" man came out - told them - it was "my" fault. They came knocking on the door - threatening to call the FCC. I offered them the phone and phone number to call. "I" knew - "my" station was clean. I called the next day - to the phone company and blasted them. The Supervisor said the "tech" was wrong to make a claim without looking around. "HE" came out - and found a bad ground on the "neighbor's" phone system. Problem solved - apology forthcoming from all. I've seen "Cable" and "Phone" installers who barely know their ass from a hole in the ground. I've seen them have to call in "others" to fix a problem.

Reply to
radiosrfun

It's not static buildup (at least the 50 or so VAC isn't).

It's probably the RFI filter caps in the front end of the power supply.

Put any sort of load between those points and the voltage will pretty much disappear. But the high impedance of a multimeter allows it to register.

If a non-polarized plug, reverse it and the voltage will probably go away also.

Where the plug is polarized and plugged directly into an outlet (no extension cords that may not be polarized), it's possible one or more of your outlets are miswired (Hot-Neutral interchanged).

Note that on equipment with 3 prong plugs and properly grounded outlets, this should not be present.

For the most part this isn't dangerous but if in doubt, have it tested.

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Reply to
Sam Goldwasser

Well what about the guy who reads the meter on your house?? Electric Meter, Gas Meter, Water meter, etc.. They all cross your property line to read the meter. Are you implying that they are breaking the law?

Reply to
Michael Kennedy

If the set has a fully isolated SMPS it would be easier and neater to fit a

3-core mains lead and earth the chassis plane on the SMPS secondary side. The cable installer would probably walk away from a set with a random looking earth wire hanging from the co-ax socket.
Reply to
ian field

If the coax outer conductor were connected to ground at some point, then the voltage would go away and maybe the cable company would be happier.

Chris

Reply to
Chris Jones

I got the impression that it was a cable system throughout the house with splitters etc. and so nobody would go looking in (for example) a wall cavity for an earth connection. Say for example that there was a splitter with a metal casing and it just happened to be bolted to a piece of metal that just happened to be earthed.

Chris

Reply to
Chris Jones

That would certainly be better than opening and modifying equipment.

Reply to
ian field

The cable system should be grounded where it enters the house. It sounds like this ground is missing, or there's an open shield in the coax. Andy Cuffe

snipped-for-privacy@gmail.com

Reply to
Andy Cuffe

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