Demagnetizer from tv degaussing coil

[senz_90]

hello everyone. okay, this is not about issue of mine tv or friends. I am just wanna learn and eager to know. the question is

could I makes a demagnetizer from degaussing coil and a single posistor from crt tv? and if that possible, the circuit which i need to built just likes how degaussing coil connected to mains voltage via posistor on scrapped tv?

any help and answer will be very appreciated.

[tom66]

Re: Demagnetizer from tv degaussing coil

I can't see anything wrong with your suggestion but what are you trying to achieve that the current degaussing coil does not do?

[senz_90]

Re: Demagnetizer from tv degaussing coil

I can't see anything wrong with your suggestion but what are you trying to achieve that the current degaussing coil does not do?

I am reading jestine yong site about monitor fault where it just show rainbow raster. he said that we need demagnetizer first to determine faults from tube or degauss circuit include coil, posistor, relay, etc (some monitor has transistor based to activated degauss funtion as he said). So i think we could waste time if we just trying to open tv case and change posistor or degauss coil, where is the real culprit if defective tube.
From this i want to makes a demagnetizer but confused about three legs posistor. i dont know how to attached series with degauss coil and two mains prong. any idea? or just connects 100watt bulb as current limiter with coil ,would function as demagnetizer?

[tom66]

Re: Demagnetizer from tv degaussing coil

You could just try this:-
http://www.youtube.com/watch?v=TyQjFrjz6xg

Never heard of a 3 legged posistor. Not sure what that is.

[redwire]

Re: Demagnetizer from tv degaussing coil

You can use a TV degaussing coil, but it will get hot quickly because it is typically on (PTC) for a second or two in a TV set during normal operation. But you need 30 seconds or so to demagnetize a CRT with a hand held coil, moving it around and fading away.
Reduce degaussing coil current with a light bulb, but the field is weaker and if it's not stronger than the magnetized stuff, then it doesn't work.
If the CRT mounting frame is magnetized, it's really hard to demag- compared to just the shadow mask.

Cassette tape machine demagnetizers also work. Or an AC solenoid.

Check the set's degaussing coil isn't ON all the time, which is what I usually see goes wrong (bad PTC). They don't have 3 leads, so you might be after the wrong part?

[senz_90]

Re: Demagnetizer from tv degaussing coil

thanks tom66.

redwire
i am sure that is ptc but have 3 legs. the black ones, and designation on pcb is PTC. This beside degauss coil. it looks hard to get a good demagnetizer from scrapped tv from your explained. how much percentage from your experienced for ptc failed that result the rainbow picture?

for degauss coil I could test it with ring tester. I just wanna makes a fast troubleshooting method about this, but it looks like i have struggle for commercial demagnetizer where is looks like nobody sell here. maybe others town.

[redwire]

Re: Demagnetizer from tv degaussing coil

Senz, you have two problems? One, the CRT is magnetized and two the degausser is not working? A picture of the screen would help.
The 3-lead boxes have PTC and a heater inside to lower residual current, they're called Posistors. I would say 90% of problems are a bad posistor. But I have seen a CRT strongly magnetized by super magnets and the degausser worked fine but was not strong enough to undo it. I have also used old AC solenoids from appliances (dishwasher, washing machine etc.) to make a wand demagnetizer.
Look how much current a TV degaussing coil gets in the graph.

[senz_90]

Re: Demagnetizer from tv degaussing coil

Senz, you have two problems? One, the CRT is magnetized and two the degausser is not working? A picture of the screen would help.
The 3-lead boxes have PTC and a heater inside to lower residual current, they're called Posistors. I would say 90% of problems are a bad posistor. But I have seen a CRT strongly magnetized by super magnets and the degausser worked fine but was not strong enough to undo it. I have also used old AC solenoids from appliances (dishwasher, washing machine etc.) to make a wand demagnetizer.
Look how much current a TV degaussing coil gets in the graph.

so Posistor box have heater insidely. I don't have a problem til now. I just wanna know how to makes a good demagnetizer, because sometimes i am help my friend to fix tv or monitor problem that's not looks very hard for me. If i could makes this i will have fast method when troubleshoot rainbow picture problem. maybe i would try the solenoid method. would you mind give me some sign likes the schema or components value? you explained well.thanks! !

[redwire]

Re: Demagnetizer from tv degaussing coil

You could make one using a TV degaussing coil and 100W light bulb. These are weak because they must degauss the whole CRT at once- that is a large area.
I use something like this, a washing machine solenoid and screwdriver, and move it around the entire screen. It takes longer.

[senz_90]

Re: Demagnetizer from tv degaussing coil

You could make one using a TV degaussing coil and 100W light bulb. These are weak because they must degauss the whole CRT at once- that is a large area.
I use something like this, a washing machine solenoid and screwdriver, and move it around the entire screen. It takes longer.

Are you add some resistor on first picture with bulb (I see it looks like a resistor)?

So the second picture AC mains plug is black and green crocodile clips right?

Tom66, what is the thing that he attached to drill? common magnet?

[senz_90]

Re: Demagnetizer from tv degaussing coil

Done !! thank you for all of you helping me. I try to make it with 100 watt bulb and trying to my tv. it has effect but i have to makes this as close as possible to see demagnetizes effect on my tube.

I haven't try it to rainbow picture tube but i think it has effect and maybe needs a longer time to degauss due to effect that i see must close to the tube, maybe not strong enough as redwire said.