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Discuss Sound Goes Off On T.v For Split Second Every Time The Wall Lights Ars Switched On . in the Industrial Electrician Talk area at ElectriciansForums.net

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PAUL M

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HI FOLKS,NEW TO THIS FORUM ,HAVE A PROBLEM THATS DRIVING 1 OF MY CUSTOMERS AROUND THE BEND.EVERY TIME HE TURNS THE WALL LIGHTS ON THE T.V. SOUND GOES OFF FOR A SPLIT SECOND ANY IDEAS OR HAVE I GOT TO ADMIT DEFEAT,SPOKE TO A COUPLE OF FELLOW SPARKS AND THEY RECKON ITS TO DO WITH FREQUENCY.HELP:eek:
 
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Grae79

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  • #2
Re: Sound Goes Off On T.v For Split Second Every Time The Wall Lights Ars Switched On

on just a bog-standard telly? no speaker cable runs to speak of?
 
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PAUL M

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  • #3
Re: Sound Goes Off On T.v For Split Second Every Time The Wall Lights Ars Switched On

no speaker cables,bog standard wide screen telly ,the wall lights are on dimmer switches ,oh and his son has a hearing aid but dont think thats the problem.
 
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Grae79

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Re: Sound Goes Off On T.v For Split Second Every Time The Wall Lights Ars Switched On

Radio frequency interference details


The modern thyristor (Triac or SCR) dimmer has one fairly severe drawback in its performance in that it dims by switching on the current to the load part-way through each mains cycle. Cutting the leading smooth-part off a mains cycle produces a current with a very rapid turn-on time which generates both mains distortions and EMI. Chokes are included in dimmers to slow down the rapid switch-on (rise time) of the chopped current. The longer the rise time the less EMI and mains distortion produced.

Turn on of the triac in the middle of the phase causes fast voltage and current changes. A typical thyristor/triac starts to fully conduct at around 1 microsecond time after triggering, so the current change is very fast if it not limited in any way. Those fast voltage and current changes cause high frequency interference going to mains wiring unless there are suitable radio frequency interference (RFI) filter built into the circuit. The corners in the waveform effectively consist of 50/60Hz plus varying amounts of other frequencies that are multiples of 50/60Hz. In some cases the interference goes up to 1..10Mhz frequencies and even higher. The wiring in your house acts as an antenna and essentially broadcasts it into the air. Cheap bad quality light dimmers don't have adequate filtering and they cause easily lots of radio interference.

Dimmer circuits typically use coils that limit limit the rate of rise of current to that value which would result in acceptable EMI. Typical filtering in light dimmers causes the current rise time (current rises from 10% to 90%) to be in range of 30..50 microseconds. This gives acceptable results in typical dimmer applications in home (typically this limitation is made using 40..100 uH coil).
If the dimmers are used in places where dimmer is a serious problem for sensitive sound equipments (theatres, TV-studios, rock concerts etc.) a slower current rise time would be preferred. Typically the current rise time in light dimmer packs made for stage applications have a current rise speed of around 100..350 microseconds. If noise is a big problem (TV studios etc.), even slower current rise times are sometimes asked. Those current rise times up to 1 millisecond can be achieved with special dimmers or suitable extra coil fitted in series with the dimmer.



there's that but it involves radio frequency interference, so shouldn't affect frequency of speakers. they aren't on the same circuit are they? :rolleyes:

try asking dragon-av, might be something he's come across before. :)
 
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wayne

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  • #5
Re: Sound Goes Off On T.v For Split Second Every Time The Wall Lights Ars Switched On

the stuff we know!!!!!
 
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PAUL M

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  • #6
Re: Sound Goes Off On T.v For Split Second Every Time The Wall Lights Ars Switched On

Thanks For That I Think I Will Change The Dimmers For Normal Switches And See If That Helps. A Pint Of Stella Please Barman.
 

danzor

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Re: Sound Goes Off On T.v For Split Second Every Time The Wall Lights Ars Switched On

no 'wife beater' here sir
 
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wayne

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Re: Sound Goes Off On T.v For Split Second Every Time The Wall Lights Ars Switched On

its well named ,
 
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dragon-av

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Re: Sound Goes Off On T.v For Split Second Every Time The Wall Lights Ars Switched On

hmmm this could be one of many things but the sound being cut is an unusaul one i cant think of anything obvious maybe check the supply to the TV with a meter and check the reading when the lights are turned on If ita a bog standard tV the speakers will be run from small 5-10W DC opamps so a small spike shouldt effect them its actually just as possible that its overdriving the amp and causing clipping. Are there any effects when the lights ar eon and being dimmed? ALso are there any "noisy" applainces (fridge freezer) close by I have known a fridge motor get all gnarly when some flourescents start that actually screwed the TV pic it only happened when frige motor was runing and lights started it took forever to diagnose!
 
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PAUL M

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Re: Sound Goes Off On T.v For Split Second Every Time The Wall Lights Ars Switched On

No The Dimmers/wall Lights Are On The Opposite Side Of The Room To The Tv,the Tv Coax Is Run Externally,the Lights Are On The Down Light Circuit And The Tv Socket On The Down Ring ,i Tested The Whole Property And Everything Was Fine ,this Was An Existing Problem When The Guy Moved In Recently.it Is A Strange One.
 
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