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Vertical bands sweeping across tv screen when dark

Discussion in 'Televisions' started by gordonfmoore, Mar 9, 2005.

  1. gordonfmoore

    gordonfmoore
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    Hi,

    I have just rewired my setup to deal with a new media center set up.

    I have an analogue tv signal coming from an outside aerial. This feeds into the aerial in of a Pace NTL digital set top box (sorry don't know which one, but is also a broadband modem and is in the Stoke area.) I take the aerial output from this and feed it into a 1 to 4 signal amp. This is then used to feed into the aerial of my tv, my vcr , my media center (split into two for dual tuner input) and via a coax back upstairs into the loft where I split it into three feeds for upstairs tvs. This is an unpowered 1 to 3 splitter.

    I also use the scart on the pace box to the tv and the scart on the video to the tv, but I don't record via the scart.

    Everything works fine, the signal quality is ace.

    However I have noticed when the tv picture goes dark that there are vertical bands going across the screen from right to left. I estimate that the strongest band takes about 1 second to cross, but there are weaker bands after it moving at the same speed.

    Does anyone have any idea what they could be? or what causes them?

    Regards,
    Gordon
     
  2. Tight Git

    Tight Git
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    Hello Gordon,

    What you are seeing sounds like cross-talk from one of the sources that you are not watching.

    It's difficult to be more specific without being there, but basically you need to unplug each source until the problem goes away.

    You may well find that it's an unscreened cable in a poor quality scart connection, but that's only a guess.

    Hope this helps.
     
  3. gordonfmoore

    gordonfmoore
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    Thanks. I'll have a muck about this weekend when the wife is out :)

    My cables are reasonably good quality though.

    Could it be interference between signal frequencies. ie the channel number that the cable box is set to, you know like a beat you get when tuning guitar strings?

    Gordon.
     
  4. Aladin

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    Try unplugging the ariel feed to the Pace NTL box. See if you get the lines still without the terrestrial feed. If you don't, install a 6db reducer to the feed from your ariel into the Pace box?
     
  5. gordonfmoore

    gordonfmoore
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    Hi,

    I've had a play and have now discovered two things:

    One: the vertical banding is actually only occuring with channel 5 - no surprise there then.

    Two: it only occurs on the loop through the cable box. Direct connection to the tv is fine.

    So assumption is that there is an interference in frequencies/oscillators somewhere.

    I assume I can change the uhf channel on the Pace box, but I have no idea how to do this - engineering menu? I wish I could easily see what model the box is, but I don't want to pull it all out!!! Maybe someone in the stoke area will have a clue as to the models generally fitted - digital stb with broadband modem? Needs redeye for working with my universal remote).

    Any more suggestions? And thanks for the help.

    Gordon
     
  6. Wackojacko32

    Wackojacko32
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    Gordon

    I think you probably right.

    If you switch the box of at the mains and then turn it back on whilst holding the channel up and down buttons on the front of the box (may need help, or very long arms :)) should get you into engineers menu where you change RF output. Rember to save settings.

    Wackojacko32
     
  7. Tight Git

    Tight Git
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    Gordon,

    Glad you've found the trouble. :smashin:

    This is a very common problem.

    The default RF output on VCR's etc is often ch38 and a lot of Five transmitters are on ch37.

    We tried to warn them at the time... :devil:
     
  8. gordonfmoore

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    Thanks for the help, I'll have a play tomorrow.

    Gordon
     
  9. gordonfmoore

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    Uhmm.

    I've managed to get into the engineers menu, what a long wait!

    I've found a page (by using the right/left arrows on the ring) that allows me to set the remodulator channel. It was set at 52. I've had it go upto 58 and down to 48, but no change on th Ch5 bands. btw my channel 5 is on analogue 35.

    There are other frequency thingies to change, but I'm a bit loathe to do that without expert guidance.

    For instance on page 1 (of 17) there is a default frequency of 666.750Mhz!!

    I'm starting to think I'm not going to win this one! :(
     
  10. Wackojacko32

    Wackojacko32
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    In that case I doubt it is the direct RF output from the box that is causing the problem. I have just returned a Pace NTL box, got Sky+ now, and found I had a lot of interference across all RF Channels, so much so that in order to find a decent RF output from Sky I had to disconnect the RF feed from the NTL Box.

    Are you aware that the NTL RF out also includes the terrestrial feed, no need for an aerial, and on my box these were in the RF range 21 - 34 approx and could interefere with your Channel 5 signal.

    IMO you have two choices

    1) unplug your aerial and retune your equipment to the NTL terrestrial feed to avoid doubling up on these channels.
    2) Get a group C/D (48 - 68) pass filter from http://www.satcure.co.uk/accs/page11c.htm to attach to the NTL RF output to allow the RF Cable signal to pass ( if set higher than 48) but stop the unwanted terrestrial channels passing through. You may wish to contact Satcure direct if this option appeals as I am not an expert, but this is what I was considering before I returned my NTL box.

    HTH

    Wackojacko32
     
  11. gordonfmoore

    gordonfmoore
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    This surprised me. I've just had a look. I disconnected the analogue aerial in and tried to see what was available. I scanned all the channels. I'm afraid with my Pace box there is no other rf out channel apart from that provided by the Pace box on Ch 52. I guess that's why it's a loop through?

    The Pace/NTL digital provides BBC ITV etc via ch 52 as part of the cable feed, but I need the analogue so that I can feed these and the NTL output into my media center for recording purposes and provide NTL and analogue to my other tvs. So I do need the aerial in.

    Unless I am totally misunderstanding you or there is a special switch?

    Thanks for the advice though. :smashin:
     
  12. Wackojacko32

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    You must have a box which doesn't separate the terrestrial channels from the cable feed. Some boxes require a separate module attached to the back of box to do this. In that case you will need the aerial feed for normal terrestrial channels.

    If you are sure that its the NTL box ouputting the interference (i.e. excluded VCR's and the like) then option 2 mentioned above may still work by blocking all signals from the box in the range that affects Ch5 on your TV. AFAIK some of the digital content can be output from the box in this range, and while your analouge tuner cant decrypt it, it still shows up as noise.

    Wackojacko32
     
  13. gordonfmoore

    gordonfmoore
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    Right, thanks for clearing that up. It was bothering me all night.

    What I've now tried is to remove the feed from the cable box and use a two to one to feed the cable and the aerial into the one to four amplifier.

    The lines have now gone away, but the downside (there has to be one doesn't there) is a tiny little bit of ghosting on BBC2.

    Gordon
     
  14. Wackojacko32

    Wackojacko32
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    Gald you found a solution of sorts :)
     

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