color tv & magnets

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hodad

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Well, today my 6 year old son discovered the trick of making the colors on the tv move around by moving a magnet across the screen.  And, as any of you who've tried this probably know, it makes  spots on the tv screen where the color is screwy.  Is there any known cure for this?  It's not all that terrible, but I have a feeling my wife will eventually ask me if there's anything we can do about it. 

Thanks
Tom
 
You effectively need a de-gauss facility which is found on some professional CRT monitors.

I believe you can possibly sort it out by setting up an electromagnet powered with low frequency AC and moving it in front of the glass (with the TV off), but I don't know/remember th specifics.

If it makes you feel any better, the lecturer at my broadcasting trainig centre was discussing HD theory using a £20,000 Sony HD CRT whilst drawing on the glass screen with a whiteboard marker to make notes. Just a shame he decided to use the strongly magnetic whiteboard eraser to take the marker ink back off.....
 
I recall a crude degaussing loop from an early heathkit color tv...  AC electromagnet...

Modern sets probably do some low level degauss every time you turn them on/off

JR
 
Hey, look at it this way, if this would have happened five years from now, you would have had an LCD screen, and he never would have had the cool magnetic experience.

It might go away, it might not.
 
Turn-off, let-cool, turn-on.

All color CRTs de-gauss. Most now do it with a coil and PTC resistor. When PTC is cold, large AC current flows; in a few seconds the PTC heats and coil current drops way off. Many sets "HUUUmmmm...." at cold switch-on; that's why.

Do it a few times. The coil neutralizes the Earth's field, is not meant for strong small magnets. But as CJ says, you may work-it-down to a tolerable level.

There used to be handheld degauss coils. Back in JR's world. Have not seen one for sale in a decade or two. Any open-core 50/60Hz coil will do, if you find an AC current to get a big Gauss without toasting it. Big open-core coils are rare. CJ could pry-open a DC-gapped choke, but still some trial-and-smoke to find a happy current.

The kid is telling you it is time to dump that bulky hungry CRT and buy a LCD or Plasma.
 
PRR said:
The kid is telling you it is time to dump that bulky hungry CRT and buy a LCD or Plasma.

Or he was trying to give an example of how poor the colour rendition is on current LCD screens.  ;D
 
I agree with Roddy--LCD's are a non-starter with me.  The good news is that turning it off took care of things--unlike when I was in college & did this to my girlfriend's tv.  It never recovered fully. 

 
I had a spot on a CRT TV from when a combo amp was placed in front of it.  I managed to get it back into shape using a tape head demagnetizer, although it took some time and "fancy" moves.

OTOH, on an LCD set, it's only a matter of time until he'd discover that driving his Hot Wheels cars over the screen makes cool rippling, multi-colored skid marks.  ::)
 
I did actually consider pulling out the tape head demagger--glad to know that's an option.  re LCD:  last night after the tv incident he was playing with a calculator & wanted to show me what happened when he pressed his finger down on the screen.  That brought another, "That's really cool, son, but please don't do it again."
 
I was going to add, before having to cut my reply short for a meeting ...You can also make a tv degaussing coil out of a bunch of wire, an AC line cord and a light bulb. 

Run 20 turns or so of insulated wire around a soccer ball or something that size to form a coil in the shape of a hoop.  Bind the hoop together with electrical tape or zip ties.  Wire the ends with an AC line cord and an incandescent light bulb (40-60-watt) in series.  The bulb will serve as a current limiter so you don't blow breakers.

Holding it a great distance from the screen, plug it in.  With the TV on, approach the screen slowly with the coil parallel to the screen, moving it around, then reverse the process to back away from the screen.  When it's out of the range of influence, unplug your DIY degausser.

I'd clear the room of anyone with a pacemaker or the like before using it.
 
OT: I took the back off my 1996 Sony 26 Inch and the black plastic just exploded into 1 million pieces when I dropped it.
So don't try to move an old TV, too many X Rays and heat I guess.

 
Under pressure from management, we replaced the CRTs in our TV studio control room with "professional" LCD monitors. I hate them... the LCDs and the management! Seriously, even these highish-grade LCDs look like ass compared to a good CRT.
 
hodad said:
I agree with Roddy--LCD's are a non-starter with me.  The good news is that turning it off took care of things--unlike when I was in college & did this to my girlfriend's tv.  It never recovered fully. 

As I understood it that might be when the 'shadowmask' has become deformed. The degaussing-coils won't fix that indeed. She still your same girlfriend ?  ;)
 

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