Could an electrical problem cause an intermittent fault with our TV?

[Debian]

Hi all,

I’m not an electrician by the way, I am just an average Joe looking for some advise.

About a month ago we bought a cheep LCD TV for the kitchen.

After a month, the TV would intermittently display a white picture, you could hear audio but could not see a picture.

I tried a different set top box, a different cable and a DVD player. The fault stayed with the TV

We took the TV back to the shop, but they could not find a fault with it.

We took the TV home, continued to use it, again the same fault happened.

We took the TV back to the shop, this time they replaced it. They did not test it this time.

After about two days with the new TV, the screen went black - again audio could be heard.

There is no pattern, some times the picture is fine, sometimes not. Once we lose the picture, we turn it off at the mains, then back on, sometimes this cures the fault. Sometimes it doesn’t.

Now we have moved the TV into another room to see if the fault follows, after two days it has not happened again.

I am beginning to think the power at the mains is faulty.

Is there a device I can plug in to the mains that would show me if mains in the kitchen was fluctuating or not providing enough output?

I had thought “we’ve got a another faulty TV”. But in our bedroom, one of the mains sockets sends my wife’s alarm clock mental. The LCD display looks shafted with a dodgy display.

I am just wondering if the mains is flaky.

We have only been here 6 months. None of the other mains outlets seem to cause a problem.

Could it me another dodgy TV?

 

[Golden_Boy]

Yes, It can - especially when it comes flat screen sets, - BTW I was a senior engineer at the dome in the Millennium - Looks like your reputations screwed! - good luck

Can you explain EXACTLY how? dont be scared to use technical language, we can take it...

 

[Sparkymarky72]

LCD-TV displays are dynamic and continually
show moving images, they have requirements that do not exist in static display applications,
like computer monitors and CRT's/ PCs.
The frequency at which the CCFL lamps is driven can interfere with the visual
image displayed on the LCD screen and a lot of screens have multiple CCFL and multiple drive I/O's so
Slowly moving lines or bars/interference can be created if the lamp frequency is not synchronised
correctly and their is a very low tolerance for this.(only +/_5%)
The same tight control is required for the lampburst dimming frequency used to adjust the brightness of the lamps.
It is a pulse-width-modulated(PWM) signal typically in the 30-Hz to 200-Hz range that turns the lamps off for a short
period of time,(microseconds)
If the burst dimming frequency is near a multiple of the vertical sync rate, rolling lines can be created.
Again, control of the burst dimming frequency to within a ±5% level will eliminate thisproblem.
Also, in some LCD-TV applications, it is necessary to synchronize the slow burst dimming frequency of the CCFL lamps to the
vertical sync rate in order to improve the image response of the LCD panel.
ALL can be affected by poor line interference as the tolerance of the drive is so low! -Happy NOW...

 

[Golden_Boy]

Hi Guys,
I am new to the forum, but I am a rare breed an AV Engineer with a 17th edition and electrical install experience,

SO HERES YA ANSWER! -

only 2 things can cause the faults your describing ..

1. IS AN INCOMPATIBILITY between the devices that are rigged up on the HDMI bus on your TV - ie one device is sending a lower/ or higher HD frequency than the other.(trying turning on/off alternatly) / or TV has a problem with a resolution its receiving. 570p 720p 1080i/p so on...(also use good HD cables) - You did say TV was cheap though...

2. The other is a frequency problem in your mains supply ie - its slightly higher/lower than 50hz or fluctuates or is dirty, - Try a filter extension lead -and get a good one - Probably going to cost more than TV did though...

An LCD tv mainly runs on low voltage DC although the mains is 240v AC it has a built in power transformer to convert to about 30-40v DC, to run the electronics Its only the screen itself that relies on the mains frequency and it also uses a power INVERTER to back light itself so you can see the image!

-A typical 40" screen only runs at about 80watts consumption-

But this inverter/convertor changes the low voltage DC voltage to around 400v DC (but not a lot of current) to light/run the screen - Its even higher in plasma screens... So you can see why resolution and mains frequncies are important.

Why Why and Why ?

And would a cold cathode backlight strike at 400 volts ????????????

 

[Debian]

Hi,

It's a Logik L24DIGB10 LCD TV.

We moved the TV back into the kitchen, we were unable to confirm the fault in a different room.

It’s so intermittent though it's a nightmare. I had the Ghana Uruguay game on, it was fine all the way through. I switched it on Saturday morning and this time the screen had a brown tinge with audio. Again I switched it off at the mains, then back on, still the same fault.

Just to confirm,

We have this hooked up via HDMI to a Freesat box.

We had the same fault using a DVD player using scart.

Both were tried separately.

The menu function on the TV displays correctly. For example, when it’s searching for a signal before selecting a source, we see a clear blue screen. I can see items on the menu clearly.

The TV comes with freeview (which we don’t use), the menu again displays correctly.

I don’t think the TV is negotiating power from external devices correctly.

I am still none the wiser if this due to a mains problem or the TV.

Both the TV and freesat box are plugged directly in to the mains - no adapter is being used.

I am taking the TV back tomorrow. Hopefully they will change it - I am going to spend a bit more and get a brand name.

I am hoping it’s not a waste of money as the TV was good value and just the right size for our kitchen.

I’ll let you know how I get on!

 

[Golden_Boy]

LCD-TV displays are dynamic and continually
show moving images, they have requirements that do not exist in static display applications,
like computer monitors and CRT's/ PCs.
The frequency at which the CCFL lamps is driven can interfere with the visual
image displayed on the LCD screen and a lot of screens have multiple CCFL and multiple drive I/O's so
Slowly moving lines or bars/interference can be created if the lamp frequency is not synchronised
correctly and their is a very low tolerance for this.(only +/_5%)
The same tight control is required for the lampburst dimming frequency used to adjust the brightness of the lamps.
It is a pulse-width-modulated(PWM) signal typically in the 30-Hz to 200-Hz range that turns the lamps off for a short
period of time,(microseconds)
If the burst dimming frequency is near a multiple of the vertical sync rate, rolling lines can be created.
Again, control of the burst dimming frequency to within a ±5% level will eliminate thisproblem.
Also, in some LCD-TV applications, it is necessary to synchronize the slow burst dimming frequency of the CCFL lamps to the
vertical sync rate in order to improve the image response of the LCD panel.
ALL can be affected by poor line interference as the tolerance of the drive is so low! -Happy NOW...

All noted and agreed with... However what connection is there to the MAINS frequency and voltage?
All the above syncronization stuff is to do with the transmitted picture NOT the mains. Otherwise how do 12 volt LCD TV's work, and why can sets be powered by generators ? or mains invertors? And what about multi standard receivers?
Also my Imac computer shows absolutly splendid TV and movie pictures









The OP was wondering if the MAINS could be causing the problems with his TV. I still maintain that this would not be so.

 

[stef]

Make up an extension lead and reverse (for TEST PURPOSES ONLY !!!) line and neutral and see if the problem
persists. So you can confirm/eliminate reversed polarity on the supply. But personally I suspect an external
connection problem I would agree with HDMI incompatibility. My panasonic DVD recorder does a similar
strange thing to my Philips TV when using HDMI.

 

[Golden_Boy]

Make up an extension lead and reverse (for TEST PURPOSES ONLY !!!) line and neutral and see if the problem
persists. So you can confirm/eliminate reversed polarity on the supply. But personally I suspect an external
connection problem I would agree with HDMI incompatibility. My panasonic DVD recorder does a similar
strange thing to my Philips TV when using HDMI.

What possible difference could that make ? Its AC for goodness sake. As soon as it enters the set there is a bridge rectifier that produces 350 volts DC. All the following circuitry runs from this 350 volt DC supply ( via a switch mode supply )

 

[stef]

I don't know, really but I think it has something to do with the phase being used by the equipment.

 

[Hundleton1]

I don't know, really but I think it has something to do with the phase being used by the equipment.

whats the score with the peeing contest going on here, i spent 12 years working in the AV industry working for a few of the majors in the UK, i don't intend to name as i don't feel i need to, its easy for anyone to talk tech and baffle the customer the real skill is being able to put that into practice and fix the problem.

as for the TV it unlikely its the mains supply, it more likely to be an environmental issue first, direct sunlight ect, if its a small set does it have a power brick rather than a built in PSU? these tend to go faulty quite often.

as for you already having had one replacement i have seen large batches of sets come in bad, i did a hotel install once and they got 20 sets from Argos, of the 20 15 were faulty, imagine we had not brought the lot that would have been the whole stores stock for some time all being bad.

i would personally take it back get something with a name you recognise, also just check for environmental changes between the rooms that could cause the problem.

 

[Spudnik]

whats the score with the peeing contest going on here.....

My thoughts exactly.

Please keep it calm.

 

[Golden_Boy]

whats the score with the peeing contest going on here, i spent 12 years working in the AV industry working for a few of the majors in the UK, i don't intend to name as i don't feel i need to, its easy for anyone to talk tech and baffle the customer the real skill is being able to put that into practice and fix the problem.

as for the TV it unlikely its the mains supply, it more likely to be an environmental issue first, direct sunlight ect, if its a small set does it have a power brick rather than a built in PSU? these tend to go faulty quite often.

as for you already having had one replacement i have seen large batches of sets come in bad, i did a hotel install once and they got 20 sets from Argos, of the 20 15 were faulty, imagine we had not brought the lot that would have been the whole stores stock for some time all being bad.

i would personally take it back get something with a name you recognise, also just check for environmental changes between the rooms that could cause the problem.

At last...........

 

[Debian]

Just to let you know, we swapped the TV for a brand name (paid slightly more though) and the TV has been fine.

Thanks for all your help!

 

[Spudnik]

Glad you got it sorted in the end.

 

[Golden_Boy]

Just to let you know, we swapped the TV for a brand name (paid slightly more though) and the TV has been fine.

Thanks for all your help!

Happy viewing