dslreports logo
 
    All Forums Hot Topics Gallery
spc

spacer

Search Topic:
uniqs
3136
share rss forum feed

pgoelz

join:2001-12-26
Rochester, MI

1 edit

Hum bars

No, not a musical joke.

Analog TVs connected directly to the cable, no STBs. For the last six months or so I have had narrow horizontal bars floating slowly up through the picture on all channels and on all TVs in the house. It is most noticeable on darker backgrounds. I have disconnected my amplified splitter (which I initially suspected) and connected the incoming cable directly to a single TV without splitter and the bars are still there. Therefore, I am nearly certain that this is present on the incoming cable feed and is not being caused by anything in the house.

The question is.... I know what they are and where they probably come from but what do I call them when I call for a service call? What term would a tech recognize? And is this something that a tech could observe without needing to look at a TV? Does the analyzer they carry measure and report 60 / 120 Hz injected into the RF? If not, I am not optimistic about CC being able to trace the problem to a particular piece of equipment.

TIA,
Paul
--
Paul Goelz, Rochester Hills, MI

Model Helicopter, music and astronomy pages:

http://pgoelz.com


gar187er
I do this for a living

join:2006-06-24
Dover, DE
kudos:5
hum bars are hum bars.....they are almost always something inside the house....cable through a coax surge, faulty tv, or vcr, etc...they can track it with volt ohm meters if the tech has one....an 860 trilitihic can see hum measurements, and newer DSAM's can if they have purchased the software....


p110011

join:2001-12-29
Oregon City, OR
reply to pgoelz
It can come from the outside cable. The fiber nodes, distribution amps. and line extenders all run off power supply's, and if a rectifier is going out, can cause hum. A bad ground can also cause it, make sure your drop is grounded. I've seen home wiring cause it (reversed leads).
If you can ask your neighbors coming from the same line if they see it, that would verify the problem from outside.

The techs know it as hum.


gar187er
I do this for a living

join:2006-06-24
Dover, DE
kudos:5
yea it can, i didnt say its impossible, but they would know its happening when they do end of lines, or see a few t/c's for it in his node...

the ground is more then likely whats causing the backfeed of voltage onto the cable if you say you hooked up just one tv and still had it....the ground is where the tech will test to see if its inside your house or on the plant...

also just try unplugging old tv's or vcrs from the a/c outlet and see if it goes away one at a time....major appliances or anything for that matter can cause it if an outlet has a faulty ground and is using the cable to ground itself out

pgoelz

join:2001-12-26
Rochester, MI

1 edit
reply to pgoelz
I think I have pretty much eliminated anything inside the house.... it is there when I connect the incoming cable directly to one TV and it is there when I disconnect just that TV from the rest of the system.

The edges of the hum bars are quite sharp and well defined so I don't think this is a simple sine wave AC line leakage to the cable shield. Looks to me more like a failed power supply cap in a line amp somewhere.

I can't dismiss grounding totally though. One thing I didn't mention was that about a year ago (and well before I think the problem started) I went over the grounding of everything entering the house. I was upgrading the grounding and bonding of the incoming AC, the water pipes, cable and telephone and my ham antennas for lightning protection. In the process I discovered that the incoming cable service was grounded to a separate (but physically close) ground rod from the rest of the house. That was not code so I bonded that ground rod to the ground rod for the rest of the house (which is also bonded to the water service). That should not have affected anything (and I am pretty certain the hum bars did not appear at that time).

My first suspicion was that they appeared when I swapped out my old 400MHz amplified splitter for a new 1GHz version. But as I said earlier, they remained virtually unchanged when I physically removed it and went straight to one TV.

Since "hum bars" seems to be a recognized term, I'll give CC a call and see what happens. But before that, I want to try one more thing.... running a totally new and separate (and totally isolated) piece of coax from the drop side of the grounding block to a TV.

Paul
--
Paul Goelz, Rochester Hills, MI

Model Helicopter, music and astronomy pages:

http://pgoelz.com


Robotics
See You On The Dark Side
Premium
join:2003-10-23
Louisa, VA

1 edit
Ive had that here at the house. And it ended up being a bad cable between the box and TV.
Maybe you have a bad cable somewhere??
Just a thought.


NSA_CIA

@charter.com
reply to pgoelz
Do you see 1 hum bar or 2?

1 hum bar tends to be 60 Hz, a neighborhood power supply or house issue is the most likely cause.

2 is 120 Hz and tends to happen when AC to DC power packs fail (which are in all cable line amps and nodes).

pgoelz

join:2001-12-26
Rochester, MI

1 edit
reply to pgoelz
The drop to the house is new as of early this winter. Come to think of it, I can't say for sure if this started at the same time or not. I don't think so. Most of it is underground. Note that we are a two cable system, so an open or flakey ground would probably have to involve both cables. Dang! That reminds me.... I never thought to check the A cable. I think there are some analog signals on it. I wonder if both cables pass through the same line amp.

There are two very sharply defined hum bars. That is why I suspect a power supply somewhere and not a ground issue.

Paul
--
Paul Goelz, Rochester Hills, MI

Model Helicopter, music and astronomy pages:

http://pgoelz.com

rendrenner

join:2005-09-03
Grandville, MI
Two bars are coming from outside the house. MOslt likely a bad coil in a power pack.

If your calling in to request a service call tell them then you have hum bars. The CAE will proally be clueless but the tech will know what it means. Make sure you request a Comcast tech and not a contractor. Not all contractors have meters so they will not be able to see the issue just by looking at the line outside the house.

No matter who shows up tho.. contractor or inhouse... unless they are driving a bucket truck they will proally not be able to repair the issue right then. The tech will verify the issue and then refer it to a network (system) tech.

Good luck and Go Wings!!


fruhead

join:2002-01-29
Mosquito,NJ
reply to pgoelz
A line tech (or field engineer) should be able to see this problem at the pole, directly off the tap. Most line engineers carry a test-set and power inverter, along with a small test-drop so they can watch the signals directly from the tap to verify a problem just like this. 60-cycle humbar is not uncommon and, since there are many things that can cause it, they may disconnect individual drops from your tap to make sure the problem isn't a 'feedback' from either your house or another, but is inherent within the system. After this is determined, repairs can proceed.

Good luck! Keep us informed on the progress.

pgoelz

join:2001-12-26
Rochester, MI
reply to pgoelz
Thanks, I'll post back here when/if it is resolved. 60 CYCLES? You must be as old as I am. Although I did eventually make the mental switch to Hz way back then. CPS just seemed more.... logical....

Paul
--
Paul Goelz, Rochester Hills, MI
Model Helicopter, music and astronomy pages:
http://pgoelz.com


fruhead

join:2002-01-29
Mosquito,NJ
yup, welcome to the Geezer Brigade.

When I was a linesman for cable,it was referred to as a 60-cycle humbar.

I remember, back in the early Cretaceous period, doing a foreman call at a house in NJ. Really bad humbar on all sets, but the field engineers would never see it outside the house. I spent about 6 hours there, and finally had it - a VCR in an upstairs bedroom (of course, in an overcrowded armoire with a beast of a TV on top of it, almost higher than I could reach) was causing it - not only when the cable was hooked to the VCR, but just from the VCR being plugged into house AC. One of the strangest things I ever found, but it took a lot of investigation and running up and down stairs to verify.

Of course, no tip.

Humbars are cagey things. They can even be caused by interference from another house that's fed from your tap feeding back into your system. Give the cable guys some patience and I can pretty much guarantee they'll eventually find the cause.


NSA_CIA

@charter.com
This is a 120 Hz humbar, there are 2 of them on screen.

More then likely not a house issue. Look at line gear power packs.


Anonymous_
Anonymous
Premium
join:2004-06-21
127.0.0.1
kudos:2
reply to pgoelz
that does not seem as bad as TWC out here in palmdale

all the tvs had diagonal lines(at lest 20 or 30of them)


NSA_CIA

@charter.com
said by Anonymous_:

that does not seem as bad as TWC out here in palmdale

all the tvs had diagonal lines(at lest 20 or 30of them)
That's usually outside electrical interference, usually from shitty house cable, loose connectors, and poorly shielded TVs.