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50V AC coming from RF connector

Discussion in 'Electronic Repair' started by [email protected], Sep 20, 2007.

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  1. Guest

    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
     
  2. Dave

    Dave Guest

    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.
     
  3. ian field

    ian field Guest

    <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.
     
  4. Guest

    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.
     
  5. Guest

    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.
     
  6. John Todd

    John Todd Guest

    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.
     
  7. Guest

    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.
     
  8. ian field

    ian field Guest

    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!
     
  9. Andy Cuffe

    Andy Cuffe Guest

    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

     
  10. Guest

    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.
     
  11. hr(bob)

    hr(bob) Guest

    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
     
  12. Guest

    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.
     
  13. Eeyore

    Eeyore Guest

    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
     
  14. AJ

    AJ Guest

    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!
     
  15. radiosrfun

    radiosrfun Guest

    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.
     
  16. 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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  17. Jamie

    Jamie Guest

    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.
     
  18. Jamie

    Jamie Guest

    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.
     
  19. 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?
     
  20. Art

    Art Guest

    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.
     
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