My tv has gone a bit funny..
Discussion
I have just noticed that my TV is distorting the image on the left of the screen about an inch from the edge. It changes the colour from a shade of blue, through to a shade of green, to red.. you get the picture. 
Anyway, does it need replacing? Or is there a way to fix it? It's a 28 inch Philips widescreen, circa 2002.
Cheers
Anyway, does it need replacing? Or is there a way to fix it? It's a 28 inch Philips widescreen, circa 2002.
Cheers
You could potentially need to get the TV degaussed.
Basically a CRT works like this.
You have a big vaccum filled tube. The screen is at one end. At the other you have a thing like three light bulbs at the end with a big metal ring by each one. The lightbulby things have a lot of electrons running through it when it gets hot. The big metal ring has a monolithic positive charge on it - in the realms of static electricity. The electrons are drawn off by the attractive force. A good number of these shoot straight through the hole in the middle and are projected towards the screen. These are the electron guns.
There are three streams produced by these, one for each colour. Left like this you would see a white dot in the middle of the screen. How does this turn into a picture you ask?
Magnets. The streams of electrons can be bent by a parralel magnetic field. This is done by a couple pairs of helmholt's coils which are like a very precise electromagnet strapped around the tube one pair moves it up and down, one moves it left and right. When running normally the beams are dragged across the screen in lines running across the screen. As a bit of a cheat it does alternate lines to make the screen flash twice as often for each picture. This makes it look smoother to the eye. This is called "interlacing"
The tricky bit is colour and this is the bit you are interested in. The screen is covered in phosphorous spots that shine a different colour when hit by the beam from the electron guns. The guns turn on and off as the magnetic field moves the beam around to draw the picture. To make it so the colours dont merge there is a mesh screen behind the phosphorous bits aligned so only the blue gun can shine on the blue dots and so on. This means that you get a colour picture and not a distorted mess.
The thing that does mess this up is magnetic fields that are not as precise as those made by the helmholt's coils. Things like badly placed speakers are a good example. These might move the beam just enough so electrons from the blue gun start hitting the red dots, and so on. This gives that lovely rainbow effect we all hate on dodgy tellys.
"I took the magnet away but the rainbow is still there! You lie!"
Congratulations. You just magnetised the metal mesh screen inside the tube. You now need to call the TV engineer out to look like a pillock walking slowly towards the TV with a gadget, while whirling it around. This is a degausser. It produces an altenating magnetic field designed to demagnetise stuff. The engineer is walking slowly towards the TV in this wierd way because doing it wrong will make it worse. You might want to not have any tapes or discs in the room at the time.
Worse case scenario. The mesh screen has become dislodged and is permanantly out of alignment. Not alot you can do about that.
Hope this is useful.
Basically a CRT works like this.
You have a big vaccum filled tube. The screen is at one end. At the other you have a thing like three light bulbs at the end with a big metal ring by each one. The lightbulby things have a lot of electrons running through it when it gets hot. The big metal ring has a monolithic positive charge on it - in the realms of static electricity. The electrons are drawn off by the attractive force. A good number of these shoot straight through the hole in the middle and are projected towards the screen. These are the electron guns.
There are three streams produced by these, one for each colour. Left like this you would see a white dot in the middle of the screen. How does this turn into a picture you ask?
Magnets. The streams of electrons can be bent by a parralel magnetic field. This is done by a couple pairs of helmholt's coils which are like a very precise electromagnet strapped around the tube one pair moves it up and down, one moves it left and right. When running normally the beams are dragged across the screen in lines running across the screen. As a bit of a cheat it does alternate lines to make the screen flash twice as often for each picture. This makes it look smoother to the eye. This is called "interlacing"
The tricky bit is colour and this is the bit you are interested in. The screen is covered in phosphorous spots that shine a different colour when hit by the beam from the electron guns. The guns turn on and off as the magnetic field moves the beam around to draw the picture. To make it so the colours dont merge there is a mesh screen behind the phosphorous bits aligned so only the blue gun can shine on the blue dots and so on. This means that you get a colour picture and not a distorted mess.
The thing that does mess this up is magnetic fields that are not as precise as those made by the helmholt's coils. Things like badly placed speakers are a good example. These might move the beam just enough so electrons from the blue gun start hitting the red dots, and so on. This gives that lovely rainbow effect we all hate on dodgy tellys.
"I took the magnet away but the rainbow is still there! You lie!"
Congratulations. You just magnetised the metal mesh screen inside the tube. You now need to call the TV engineer out to look like a pillock walking slowly towards the TV with a gadget, while whirling it around. This is a degausser. It produces an altenating magnetic field designed to demagnetise stuff. The engineer is walking slowly towards the TV in this wierd way because doing it wrong will make it worse. You might want to not have any tapes or discs in the room at the time.
Worse case scenario. The mesh screen has become dislodged and is permanantly out of alignment. Not alot you can do about that.
Hope this is useful.
miniandy said:
Thanks for the advice. Some more helpful than others!
I only have a sub that sits behind the tv - I'm guessing that it's shielded? It's been there for over a year and a half..
Subs have big to very big magnets in the speaker. Friend of mine put his sub near his TV and it never recovered!
New (powered) subs tend to be shielded though.
Thanks for taking the time to explain it. Gassing Station | The Pie & Piston Archive | Top of Page | What's New | My Stuff