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  1. #21
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    Default Re: voltage in cable coaxial

    Quote Originally Posted by gadient View Post
    I have this problem and I am a technician. The cable guys are at a loss except to blame it on my house. We have traced the source of the backfeed to the cable modem itself. That means the problem has to be from my house current. We tested this from an outlet with a solid ground (according to those little testers) and found 50 some volts. The cable techs tested the same modem outside from a generator and there was no voltage. I am racking my brain to try to solve this issue. The techs were surprised to find the voltage comes from the modem itself. Apparently it stores in the splitters (which are grounded) until it reaches a threshold that takes out my service. Then I can discharge it and get it back up. Any ideas?
    If you are a " technician " , then you should have access to some decent test equiptment . I'm not sure what you mean by " those little testers " , but you need something better if you are going to troubleshoot this problem . You say you have 50 volts ? Where exactly ? AC or DC ? If it's AC , what is the frequency ? How are you testing the ground ? How , or what , are you " discharging ?

  2. #22
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    Default Re: voltage in cable coaxial

    Also --- if you are a technician then tell me how a cable splitter can " store " a charge and " discharge " ?

    If the modem has 50 or 60 volts coming out then there is a problem with the modem.

    If there is 50 or 60 volts measured on the cable line then it's the cable company that has an issue.
    "" an ounce of perception -- a pound of obscure "
    - Rush

  3. #23
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    Default Re: voltage in cable coaxial

    Quote Originally Posted by djohns View Post
    If you are a " technician " , then you should have access to some decent test equiptment . I'm not sure what you mean by " those little testers " , but you need something better if you are going to troubleshoot this problem . You say you have 50 volts ? Where exactly ? AC or DC ? If it's AC , what is the frequency ? How are you testing the ground ? How , or what , are you " discharging ?
    Good questions: I have been a tech since 76 - research, computer-integrated manufacturing tech, electronics engineer, and now IT manager. The comcast guys had the meter but I assume it was dc and about 51 to 54 volts. It varies somewhat. The modem is installed in a non-grounded outlet but we also tested it on a grounded outlet. We first tested a surfboard voip modem and then an rca. Both have non-grounded, non-polarized, plugs. We tried reversing the polarity with no difference. The "little tester" is a simple outlet tester with the 3 leds that shows if the outlet is grounded, etc.

    The techs did all the measuring. I am going to take the modem into work tomorrow to see if it happens there. I'll bring my meter home and test it here so I can better answer. I guess they measured it between the shield and the signal wire since there is no ground in the room. They also checked it between the signal wire and the ground of the grounded outlet.

    The techs tell me the splitters act as a capacitor and so that is what we discharge. I don't have a scope but my meter at work is fairly decent. I haven't been into electronics for a number of years but I'll see what the meter will do. The only way I tested the ground (i really didn't) was with "the little tester". They tell me the problem is in my house because none of my neighbors have a problem.

    Ground loop may be a possibility but I don't see how my line voltage (errors?) can get through the cable modem transformer to backfeed voltage. Would a diode help? I also have not tried a (cable) surge suppressor.

  4. #24
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    Default Re: voltage in cable coaxial

    Isolate the cable service from your house at the demarc box . See if you read a voltage on YOUR side of the cable . If not , then you know it's coming from the cable company . If you do , then you're going to have to start tracking down the source . Unplug TV's one at a time and measure . Unplug modems , routers , etc. , and test . They might have done all of this , but it won't hurt to start over and use your own logic .

  5. #25
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    Default Re: voltage in cable coaxial

    Darn --- dj beat me to it .
    "" an ounce of perception -- a pound of obscure "
    - Rush

  6. #26
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    Default Re: voltage in cable coaxial

    Quote Originally Posted by gadient View Post
    Good questions: I have been a tech since 76 - research, computer-integrated manufacturing tech, electronics engineer, and now IT manager. The comcast guys had the meter but I assume it was dc and about 51 to 54 volts. It varies somewhat. The modem is installed in a non-grounded outlet but we also tested it on a grounded outlet. We first tested a surfboard voip modem and then an rca. Both have non-grounded, non-polarized, plugs. We tried reversing the polarity with no difference. The "little tester" is a simple outlet tester with the 3 leds that shows if the outlet is grounded, etc.

    The techs did all the measuring. I am going to take the modem into work tomorrow to see if it happens there. I'll bring my meter home and test it here so I can better answer. I guess they measured it between the shield and the signal wire since there is no ground in the room. They also checked it between the signal wire and the ground of the grounded outlet.

    The techs tell me the splitters act as a capacitor and so that is what we discharge. I don't have a scope but my meter at work is fairly decent. I haven't been into electronics for a number of years but I'll see what the meter will do. The only way I tested the ground (i really didn't) was with "the little tester". They tell me the problem is in my house because none of my neighbors have a problem.

    Ground loop may be a possibility but I don't see how my line voltage (errors?) can get through the cable modem transformer to backfeed voltage. Would a diode help? I also have not tried a (cable) surge suppressor.
    The spitters are simply distribution taps with cheap ceramic filter caps ( not electrolytics ) to filter low frequencies.
    This is why when splitters go bad you start seeing a noisey picture on channels 6 and lower.
    I don't see how they would store 50 - 60 volts.

    If they hooked the equipment up to a generator ? this lifted any ground loops.
    Besides, if the cord is ungrounded then they may not have a ground block on the cable line installed or it may not be bonded properly.

    Maybe you have to get a car battery and invertor to run the modem
    "" an ounce of perception -- a pound of obscure "
    - Rush

  7. #27
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    Default Re: voltage in cable coaxial

    Quote Originally Posted by canuk View Post
    Also --- if you are a technician then tell me how a cable splitter can " store " a charge and " discharge " ?

    If the modem has 50 or 60 volts coming out then there is a problem with the modem.

    If there is 50 or 60 volts measured on the cable line then it's the cable company that has an issue.
    That is the cable techs idea that the splitters act as caps. It has happened with 2 modems so they think it's impossible to be their problem. The voltage comes straight out of the modem - unconnected - backfeed.

  8. #28
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    Default Re: voltage in cable coaxial

    Quote Originally Posted by gadient View Post
    That is the cable techs idea that the splitters act as caps. It has happened with 2 modems so they think it's impossible to be their problem. The voltage comes straight out of the modem - unconnected - backfeed.
    Of course ---- many of them are --- ummm -- just cable techs.
    "" an ounce of perception -- a pound of obscure "
    - Rush

  9. #29
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    Default Re: voltage in cable coaxial

    Quote Originally Posted by djohns View Post
    Isolate the cable service from your house at the demarc box . See if you read a voltage on YOUR side of the cable . If not , then you know it's coming from the cable company . If you do , then you're going to have to start tracking down the source . Unplug TV's one at a time and measure . Unplug modems , routers , etc. , and test . They might have done all of this , but it won't hurt to start over and use your own logic .
    Measuring voltage in the attic where the splitters are without the modem connceted there is not much - maybe 5 volts - I forget. The techs were shocked that I proved the voltage came from the modem but they still want to blame it on my house. I don't understand your first sentence. Isolate how? demarc box? I dont know too much about cable. I would also like to believe it is a defective modem but it is the second one.

  10. #30
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    Default Re: voltage in cable coaxial

    Quote Originally Posted by canuk View Post
    The spitters are simply distribution taps with cheap ceramic filter caps ( not electrolytics ) to filter low frequencies.
    This is why when splitters go bad you start seeing a noisey picture on channels 6 and lower.
    I don't see how they would store 50 - 60 volts.

    If they hooked the equipment up to a generator ? this lifted any ground loops.
    Besides, if the cord is ungrounded then they may not have a ground block on the cable line installed or it may not be bonded properly.

    Maybe you have to get a car battery and invertor to run the modem
    All great ideas. Thanks for helping me with this. You guys are great. I keep telling them the problem is in the line and that it must be some kind of ground loop but they just blow me off. They say they have "done all that they can" to solve the problem. They have been out to my house at least 20 times.

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