TV signal dies when a light is turned on - stumped!

Discussion in 'TV & Satellite' started by The Lobster, Jun 17, 2016.

  1. The Lobster

    The Lobster Funster

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    I'm getting a problem with my TV - any ideas to diagnose/fix it? It works fine and picks up all expected freeview channels (including the HD ones)... until some of the interior lights are turned on. Depending on which ones are turned on the signal either disappears completely, or reduces enough to cause occasional picture drop-out.
    • I've checked the TV on both 12v and 240v, and on different sockets - no difference.
    • It works fine on other sources (e.g. DVD or USB), and fine if I take it into the house and try it on Freeview or satellite.
    • Inserting an "earth break" aerial connector makes no difference.
    • The signal booster was fitted by a previous owner and is spliced into existing wiring - if I disconnect the signal booster power lead this makes no difference.
    • Removing the separate signal booster (and just connecting the aerial directly to the TV via an inline aerial connector) makes no difference.
    • The aerial and aerial cabling signal or shield is showing no shorts and no voltage against earth, whether the lights are on or not.
    However I'm still thinking that this might be some sort of earthing problem - if I simply touch/hold the aerial cable near the aerial (even on an insulated area) the signal is restored - although not if I try that near the TV.

    Stumped!
     
  2. Barclaybasher

    Barclaybasher Funster

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    Had a problem with my tv, sound would go off if I used a tap,

    cause..... leisure battery going flat
     
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  3. hilldweller

    hilldweller Funster Life Member

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    Are the lights LED ?

    Some kick out electrical noise that could be the problem.
     
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  4. Flamenca

    Flamenca Funster Life Member

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    Are the lights you switch on fluorescent? If so they might be feeding interference back into the 12 volt circuit.
     
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  5. John Laidler

    John Laidler Funster

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    I would have thought it was something like that. It might be possible to fit a suppressor across the inlet terminals to the lights which cause the problem. You may have to disconnect the lights first then reconnect them one by one until you can isolate the one causing the problem. Then either replace it, it may be about to fail anyway, or fit a suppressor. Car accessory shops should sell them though they will probably be big.
     
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  6. The Lobster

    The Lobster Funster

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    Yes they are - I did a test by swapping one back to the old halogen bulb and the problem wasn't present! I monitored the TV signal strength with halogen vs LED and could see a very marked difference... this would also explain why putting my hand near the LED bulb reduced the interference. I also re-discovered how hot halogen bulbs get - ouch!

    Full marks for diagnosing the issue within seconds of me posting... now I'm wondering what to do about it. A judiciously placed ferrite bead? Hope I don't have to replace all the LED bulbs... perhaps a little 1.5nF capacitor across their legs might help. Might try that.

    From what I understand these small LED bulbs typically require a switching current regulator (which causes the interference) but do not include radio interference suppression components because of the package size... although apparently some bulbs use a "linear" regulator (no switching so no radio noise)... but I can't find any :(
     
    Last edited: Jun 17, 2016
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  7. The Lobster

    The Lobster Funster

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    So now that I start searching for "interference from LED bulbs" it's clear that this is a major issue with the technology - and yet I never spotted it before replacing the halogens in my MH, which is annoying. It also appears to be difficult to identify which LED bulbs will cause interefence, and which won't - this doesn't necessarily appear to be price related, for example. Super!
     
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  8. hilldweller

    hilldweller Funster Life Member

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    Yes they use resistors to regulate the current. Any advertised 8..24V will be switch mode. Something like 12..15V will be resistors and cheaper.
     
  9. Lenny HB

    Lenny HB Funster

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    The cap may work might be easier to fit a ferrite core on the TV power lead if it hasn't already got one.
     
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  10. The Lobster

    The Lobster Funster

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    They were all advertised as 12V only un-dimmable... looking at the adverts again gives no indication at all as to the regulator type.
     
  11. The Lobster

    The Lobster Funster

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    I
    I've got some clip-on ferrite cores coming tomorrow - I'll try them at both ends...
     
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  12. hilldweller

    hilldweller Funster Life Member

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    Worth a try and cheap.
     
  13. Don Quixote

    Don Quixote Funster

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    If your 12volt cable from the TV to the supply socket is very long this can acted as an aerial. Try making the cable as short as possible or at least less than 3 feet or 1 metre. Ferrite cores may work, but make sure they are coiled (cable) a few times around the core. Good luck
     
  14. WillH

    WillH Funster

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    We have a digital radio in the kitchen at home and it is very sensitive to our led lights. I suspect that this may be a problem.
     
  15. The Lobster

    The Lobster Funster

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    So, results so far: the TV already had a ferrite core in it's power lead, so adding one there made no difference. Adding clip-on ferrite cores to the smaller (G4) bulbs solved the problem completely for them :) However the bigger MR16s weren't fixed by this - possibly because I can't position the ferrite cores as close to the bulbs. I have some small capacity capacitors on order, so I'll try those instead when they arrive.
     
  16. The Lobster

    The Lobster Funster

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    If you read the threads around the web regarding "interference from LED bulbs", most refer to problems with DAB and LED down-lighters :(
     
  17. Don Quixote

    Don Quixote Funster

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    Well I have both DAB and TV running fine without problems and the MH is full LED'd which I fitted 90% myself, must be very lucky.
     
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  18. SuperMike

    SuperMike Read Only Funster

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    As already, mentioned it seems that it is simply down to the quality of the LED's and their associated circuitry. Were they cheap ones like those sold on Ebay ? If so, I would not fiddle around with them, take them out and put in decent ones, like from Aten Lighting.
     
  19. tonyidle

    tonyidle Funster

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    It may be that the 'decent' ones, that have regulators, are the cause. LEDs on their own do not cause interference. Switching regulators can and do. My van is full of Chinese eBay LEDs that have no effect on either DAB or TV. Two failures so far out of 16 modules installed.
     
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  20. SuperMike

    SuperMike Read Only Funster

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    Perhaps you are right, but it would be worth changing one to see what happens. Just an idea. Aten Lighting, no failures so far out of 33 modules installed. :)
     
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