Common Problems- Hum Bars

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Hum Bars

A single line rolling up the screen indicates a general grounding issue.
If the cable is NOT currently grounded to the homes electrode system then bring the groundblock up to specs by grounding to power.

If the cabling system is currently grounded to the homes electrode system then temporarily disconnect the ground to see if the Hum is resolved. If the Hum Bar does resolve itself then the issue is a ground loop between the homes electrical system and cable. An outlet/polarity tester can be used to yield further clues as to the homes electrical systems integrity. If the polarity test fails or the homes electrical system is at fault the fault will rest with the homeowner. Replace the ground and advise the homeowner of your findings.

Another possible cause of Hum can be a neighbors home. This is commonly called "AC BACKFEED". Troubleshooting steps include climbing the pole/accessing the ped and disconnecting each active drop while keeping your customers active to see if the HUM disappears. Having the sub on the phone/cell is extremely efficient. If the HUM is originating from a neighbors home verify their status as an active customer and follow the above troubleshooting steps again at their home.

A double line rolling up the screen is indicative of a power pack issue at the amp. Forgo all above troubleshooting steps and jump straight to a test set off the tap or a test drop to the customers set. The problem is usually traced back to the closest amplifier housing a failing power pack. Ensure groundblock is up to specs and refer to your maintenance crew for repairs.

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hum could be a result from a defect power Pack in a Amplifier

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hum could be a result from a defect power Pack in a Amplifier

Got it covered in the above post.. although I guess the first sentence should be POWER PACK as opposed to Power Supply....

Hum Bars

A double line rolling up the screen is indicative of a power supply issue.  The problem is usually traced back to the closest amplifier housing a failing power pack. Ensure groundblock is up to specs and refer to your maintenance crew for repairs.

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Ho sorry

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might want to note ive seen hum bars from a defective house amp and or house amp power supply as well.

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Good one! I havent run into a bad house amp yet. I was at a house however a few weeks ago with Hum on a flatsrceen. Sub said he would call me when I could come back out, he didnt have the time.
His basement was all DIY however.. wouldnt be shocked to see an amp down there.

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I would say that 99% of all visible hum in the cable system comes from bad power packs in line extenders or from inside the customers home.  But if you hit a dead end there than there are several other culprits like low line voltage or wrong voltage setting on a distribution power pack (120Hz), bad filter capacitor(120Hz), bad power supply diode(60Hz), loose connector with corrosion(60Hz), bad AGC.

If you don't have an outlet checker and are willing to spend the time at a customers home, you can also flip off one breaker at a time in the home checking the hum on the TV (hopefully they have more than one TV) each time until you isolate it to one circuit.  If it is not obvious which electronic component, dimmer switch, ceiling fan, etc. that is causing the problem mark the breaker and tell them to call an electrician.

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Very Good Thread 
*Bump* to keep it near the top as some excellent tips for service guys. If any MT got anything useful out of it, then I gotta ask...
HTH did you get in maintenance to begin with... 

If you ever disconnect a drop and blow out every appliance in the house because the owner did some "addition" work on their own and the TV's start smoking... you will remember that call.
You some dedicated MoFo's to troubleshoot an customers house for some faulty AC... I verify where the problem is and show the customer the proof and ask them to turn off the breaker for that run until they can have an electrician fix it. I know they are going to turn it back on when I leave which is why I put an low-RF filter on their line to keep from killing my noise levels in that node.
This specific customer was not allowed to be hooked back up till an certified electrician called us with the OK... and then we doulble checked before doing so.
He's the only one I didn't leave until I verified inside the home that he had 240 (220) coming out of all his 110 outlets.

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I've been on multiple calls and found the source of the hum bars to be a a bad power supply in a new TV. The give away on this is a new set with highly visible hum bars and all other sets showing fainter hum bars. Unplug the new set and show the customer that the hum bars went away on all other sets.

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Had a battle with humbars on an HD tv the other night.  Switching to hdmi worked but I can not figure out the technical reason why. If anyone cares to share some insight it would make me very happy.

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Had a battle with humbars on an HD tv. Switching to hdmi worked but I can not figure out the technical reason why. If anyone cares to share some insight it would make me very happy.

Same worked for me a while back. It was driving me crazy, was amazed (and happy) when the bars went away.

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 The main causes I have found are as fallows. The cable system becomes the ground for the customers equipment. This can present as simple voltage at the box or a hum bar. Here it tends to be our modems witch use a third prong for ground being plugged into a power strip that isn't grounded. The third pin on our equipment becomes a ground for the strip. Sometimes you will see with a hot neutral revers on the outlets with tv's plugged in they will start to use the cable system for a ground as well. The old game system channel adapters were bad for a noise back feed threw a splitter as well.

Any ways a good tool to keep handy is one of those cheep three prong outlet testers. They can give a good idea about what your plugging the power into. Also watch out for a floating or lifted neutral That will cause all kinds of not fun problems and tend to burn up equipment, and hurt techs. 

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Had a battle with humbars on an HD tv the other night.  Switching to hdmi worked but I can not figure out the technical reason why. If anyone cares to share some insight it would make me very happy.

Ihave seen this as well and also resolved wiht HDMI.
What about boxes that have hum through the RF out? same principal?

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The main causes I have found are as fallows. The cable system becomes the ground for the customers equipment. This can present as simple voltage at the box or a hum bar. Here it tends to be our modems witch use a third prong for ground being plugged into a power strip that isn't grounded. The third pin on our equipment becomes a ground for the strip. Sometimes you will see with a hot neutral revers on the outlets with tv's plugged in they will start to use the cable system for a ground as well. The old game system channel adapters were bad for a noise back feed threw a splitter as well.

Any ways a good tool to keep handy is one of those cheep three prong outlet testers. They can give a good idea about what your plugging the power into. Also watch out for a floating or lifted neutral That will cause all kinds of not fun problems and tend to burn up equipment, and hurt techs. 

The humbars were not present on any tv other than the tv with the converter and only when using the converter, meaning cable directly into tv they were not there.  Happened with tv and converter plugged into different electrical outlets or the same outlets and happened even with a VBC between the converter and the cable. Happens with or without cable being bonded, hooked up to splitters and without the drop connected still produced the humbars just not as intensely. Cable thru vcr without converter produced a clear pic converter without rf produced a clear pic.  I dont get why just our cable box is affected and no other device that uses rf nor why it was only present using component and not via hdmi.

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If using the coax connection between the box and tv, did you try a vbc on that line? With all other connections off.


I haven't ran into the problem with the boxes yet.