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

 

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.

 

<snip>

Unless your TV has an earth connection (3-core mains lead) the chassis
ground is connected to the mains in filter, this effectively means that the
chassis is connected to a capacitive potential divider across the mains
input complete with high value parallel bleed resistors.

 

TV has 2 prong plug. I tested 4 different TVs that did this and 3
that didn't. 2 of the 3 that did where big screen projection TVs and
the other was a highend JVC CRT. The 4 that do this are run of the
mill brands Panasonic, RCA, Magnavox.

In plain english is this something that is suppost to happen with
lesser TVs? or are all 4 of them broken in some way?

Cable company says they can't hook up TVs as long as there is AC
coming from TV to ground when they use a multimeter. From what I read
TVs do output some AC until the cable is connected and with the proper
tester leakage if present can be detected. But a simple voltmeter
will ALWAYS read AC if RF from TV is not connected to anything. Is
that the proper understanding or am I out to lunch.

 

2 of the 3 that did where big screen projection TVs and
the other was a highend JVC CRT.

should read

2 of the 3 that DIDN'T where big screen projection TVs and
the other was a highend JVC CRT.

 

Is the power cord of those small TVs a polarized type? If not, did
you try reversing the plug in the socket and remeasuring?
I wonder if you might have a ground fault in your house? You could
try one of those $10 testers in all the TV power outlets.

 

Got a tester from electrician and tested all sockets all had correct
polarity and grounding. Electricians checked the ground and neutral
to copper pipe and all was good there as well. I'm leaning towards TV
is suppost to do this but no concrete proof yet.

 

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!

 

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

 

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.

 

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

 

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.

 

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

 

Had a very similar situation with a customer location. Once the CABLE
COMPANY came out and installed the grounding block properly, I.E., properly
connected to a known good ground source, not just the black metal pipe that
it had been tied loosely to before. LOL!! Elimited the supposed
current(Leakage Voltage ??) and improved the reception. DUH!
Compentency seemed lacking in regards to the initial installer, IMHO!

 

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.

 

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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Put a 75 Ohm R in the F-Connector and then test across it.
I think you'll find the voltage to not use as much any more.

 

The cable company coax is also suppose to be grounded. We had an issue
here for some time with a 60 hz hum bar appearing in my DLP 61" only
when watching analog broadcast and not digital.. We use a box from the
cable company to get that service. any ways, after 2 calls of a dead end
with 2 different service tech, they both try to tell me it's was my
equipment even though it was their box that was introducing the noise
from their system.
So I fixed it my self by replacing the ground rod out side my home
that lost it's bonding to earth which belongs to the cable company.

Problem was resolved. Since i'm more or less in the business I sent
them a bill. Yes, I sent them a bill. they sent out 2 other techs to
verify what I did and then try to bill me double of what I charged them
for the 2 tenchs they sent out.
That quickly got resolved when I stopped by their local office to
notify them that an arrest was going to be made for sending 2 tenchs out
and entering on my property with out notice. They not only had did that,
but they entered a back side of my home to gain entrance to a shed I
have where their wire goes in. Even though the shed wasn't locked. They
entered illegally. I had them and they knew it. I got what I asked for
and 6 months free service for the problems.

A think 2 months ago, an electrical technician entered on some one's
property to do some work on the meter. they entered through a wooden
gate with just a simple bolt latch. the Electric company never called a
head to notify them coming. Well, these people have a dog inside that
fence and it is trained not to let any one leave. Even though nothing
happen as far as the dog. The electric company call the animal control
people. They arrived and asked if they called the owner first?
apparently the electric company thinks they are above every one. They
told him that they don't need to do that and just do his job. finally a
neighbor was able to get in touch with the owner which was at work.. he
got there and just simply walked in and open the gate to let him out.
The owner is now pressing for trust passing. It seems that a lot of
mysterious home robberies have be taken place during the day while
people are at work.

Gives you something to think about.

P.S.
Cable or Electrical Techs are not legally allowed
to go past the boundaries of any open terrain to which
their wire leads. This means, they don't go inside or
open doors to access points that are set by the owner of
said property with out first notifying and setting up an
appointment or getting permission to do so.

This was told to me by a retired telephone technician.

 

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?

 

Sematically yes!! However if you look into your contract(s) with the
residential service companies you may be suprised to find that you're
ageeing to allow their verified service representatives access to what is
termed 'Their Service Corridor', meaning they can legally go onto your
property to do nominal maintanence and read meters for billing purposes.
However, it is only PROFESSIONAL for them to call ahead if they will be
intruding into nominally posted areas having animals, etc.