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3.9 Member Questions

I had this problem in my house and after a lot of experimenting was able to track it down to the cable running into the house was running too close to the electrical. The cable was wire-tied to the main electrical feed for the house on the outside, and running over the top of the electrical box in the basement. After replacing the feed into the house with RG-6U, drilling a new hole into the house, and running the cable a few feet from the electrical, the problem went away. My advice for troubleshooting, try attaching a single TV to the cable feed on the outside of the house first. I did that by simply running some RG-6U out the door on the ground and connected it directly to the feed from the pole and to a TV. If the horizontal bar (hum bar) goes away, the problem is most likely caused by a cable wire somewhere running too close to electricity.
(Thanks for fmook for this one.)

Editor's Note: That horizontal bar is called a "hum bar".

Note by Tech3912 See Profile: Also bad crappy amps will do this as well. We see it alot as techs becuase ppl go to radio shack and get screwed... :)

Feedback received on this FAQ entry:
  • This can also appear as an annoying hum in the audio system. Home theaters and computers attached to cable modems are subject to this. In my case I have both horizontal bars and humming sound. I had a home theater system and the computer computer affected by this problem. Both the TV and the computer monitor were showing horizontal bars and the humming could be heard in the speakers of both systems. The computer was attached to the cable modem and then there is an audio cable from the computer to the home theater. The only solution was to install a ground isolator at the main cable coming from the outside.

    2010-06-24 00:09:04 (printscreen See Profile)

  • Also ......A bad electrical ground, via ground block will usually cause this. Make sure all ground wires are secure and proper. HD TV is usually the worst and first channel where you will see this. The ground should be attached from ground block to electrical ground rod, electrical service pipe or copper ground wire via rod. Grounding to inside copper or galvanized pipe is never a good idea but will work.

    2010-04-13 19:05:11

  • Ground loop - ground from cable (coax) is using the same ground as the power to the TV. with both units plugged into the TV, there is a ground loop induced in the TV. Remove the ground for the TV, or reduce the size of the loop.

    2009-12-19 22:14:45

  • humbars are caused by bad grounding (most of the time from what I have seen). In a modern house with 3 pronged plugs you will never see a humbar because the TV grounds out the CATV system, however if you have a non grounded drop running to a TV that has no ground you can allmost garantee that you will see a humbar. I run my arrial drops directly to power meters 90% of the time right along the threephase distro and even behind the meter base down to the power meter and never ever see humbars unless I haven't grounded yet.

    2009-04-10 21:07:24

  • Bad picture tubes is usually the main cause I run into. Try popping in a dvd or vcr tape and unhooking the cable line from wherever its going(into tv or vcr for example) if the lines are still running across the tv in anyway, up down, left right, then you know its not the cable line. I had a guy pay the cable company $75 for the service call for me to show him this and explain to him he needed a new tv or to get his fixed which I recommended not doing these days, unless its a pricey set.

    2008-12-06 03:58:47

  • cableguy78199- humbar issues can also be caused by an improper ground. the ground wire at the pre-wire should be on a ground rod or cold water pipe, nothing else!

    2008-04-06 15:54:45

  • hum bars can also be from poor grounding at the home

    2007-09-22 03:13:51 (jpalen See Profile)



by Raydr See Profile
last modified: 2005-05-17 10:41:08

I think in most cases, anything electronic will die suddenly when a component quits working.

However, say you have a component in the cable modem that only malfunctions when it gets hot....and each time it malfunctions sooner and sooner, it's eventually going to stop working.

Feedback received on this FAQ entry:
  • Something I often share with friends when they tell me stories of how they've had to replace their modems multiple times, is to think about what kind of external factors could be impacting the device itself. As an example, in my home I went through 4-5 different modems throughout the course of a single year; I immediately stopped having modem issues after purchasing a battery backup. I had a surge protector prior, but my issue was actually stemming from intermittent and irregular power flow. Brown-outs. Electricians I have spoken with suggest it's very possible for smaller 'always on' electronics to have issues if the power source isn't constant. This would include cable boxes as well. Now I don't plug just my TV into the battery back-up, but my digital boxes as well. Smooth sailing ever since. Something to think about...

    2012-11-30 00:18:51 (S1R1US See Profile)

  • From what I gather, the standby switch doesn't power anything down, at least not on my Motorola unit. The modem still maintains sync with the cable network and the device(s) on the local end which is how it can reconnect the instant you take it out of standby. Standby mode just breaks the link between the two networks.

    2008-07-13 02:53:01 (koolkid1563 See Profile)

  • cableguy78199- most cable companies will tell you to leave your modem on all the time(especially if you bought it from them) they are full of it! would you leave your tvs on all day when your not watching them? if you did they wouldnt last too long. so turn them off when not in use, theres usually a standby switch at the top.

    2008-04-06 15:59:32



by Raydr See Profile
last modified: 2005-05-17 10:37:39

Most likely a signal issue. See modem troubleshooting section.

Feedback received on this FAQ entry:
  • This is 100% true. I've also noticed significant improvement in my digital box performance after switching to a battery backup. I'd certainly recommend connecting networking equipment such as routers to a battery backup too.

    2012-11-30 00:21:31 (S1R1US See Profile)

  • A large majority of problems reported with cable and DSL modems that are repaired by resetting or rebooting are caused by flaky power. An uninterruptible power supply (UPS) is a MUST for any computerized equipment if you expect reliable service. If you already have your equipment protected by a UPS, check and replace the batteries every 2 years. This is well worth the savings in irritation from failures of equipment on which we depend more and more.

    2012-06-28 02:15:48 (BoteMan See Profile)



by Raydr See Profile
last modified: 2005-05-17 10:38:22

No. Comcast, like almost all U.S. cable companies, will not activate a box that is not rented from them. This is due primarily for security concerns.

Feedback received on this FAQ entry:
  • they are talking tv converter boxes not cable modems

    2009-08-29 02:51:52 (ajwees41 See Profile)

  • thats not entirely true, alot of our QAM channels are not encoded, you can buy converter boxes and get most of the channels when you only have a limited cable package. The wierd thing is though that when you do that the channel line up will be way out of order. Also of course you won't get ondemand showtime hbo ect. I think you will get all of the digital starter channels though I haven't ever bothered to check and see.

    2009-04-10 21:12:24

  • With Time Warner Cable here in NY City, customer purchased modems WILL work provided the MAC addresses are on file with our IT Department and matches the current account that the HSI service is being billed that will use it. Provided the modem meets DOCSIS specs and can operate on 687.000 MHz, it will work.

    2009-01-15 19:13:07

  • This is changing a LOT. Just went to Comcast's site in Minneapolis to check for my mom, and they implied they'd rather see you buy a modem - saves them hassle. (They gave her one in the end, just makes it easier.). And Time Warner Cable in Milwaukee definitely has a provision for customer modems.

    2008-09-30 01:13:43 (bbgrunt0 See Profile)



by mbernste See Profile edited by Raydr See Profile
last modified: 2005-05-17 10:40:30

A ground block is a item generally placed on the outside of a residence between the cable drop and the internal wiring of a home. A ground block bonds the sheild of coax to the electrical ground of the residence. A ground block is usually connected by solid copper to either a cold water pipe or to the ground of the electrical service drop.

In the attached image the large arrow points to the ground block itself, while the smaller image points at the ground connection.

Click for full size


Feedback received on this FAQ entry:
  • Glad I could help!

    2009-01-21 23:17:29 (Axilla See Profile)

  • you are awesome! You posted this while I was still reading the FAQ, thanks.

    2009-01-21 22:43:41



by Axilla See Profile
last modified: 2009-01-21 22:34:38