reversing magnet damage to picture tube

[lguise]

i found out the hard way that you shouldn't place a magnet near your tv. is there any way to reverse the damage?

[OvenMaster]

I did that once. Ten minutes of a tape head demagnetizer moved in circles near the discolored areas fixed it. Same principle as a degaussing coil.
Tom

[John Marinello]

There is a degaussing coil built into (almost) every color TV. The coil is energized breifly when the set is turned on, and you can usually hear the hum when it does. This is usually enough to remove any magnetism from in & around the CRT. To cycle the degauss circuit, just turn the set off for a while to let it cool down, then flip it back on to see if the "damage" goes away. If, after a few power cycles, the magnetism isn't removed, then you'll need to either borrow or build a stronger degaussing coil.

[Eric H]

A Weller Soldering Gun does a good job of degaussing, turn it on near the face of the tube, move it in circles and pull it away slowly then shut it off when you are several feet away.

[avionic]

Lifesaver for those badly magnetized CRT's.If the CRT is really messed up the built in degaussing coil just won't do the trick,Weller solder gun just doesn't cover enough area-it may work but I would think it would take quite a few trys to get her done. When I was in TV field service many moons ago,this was the gauranteed first time, everytime cure for the magnetized screen.
http://www.electronicsporium.com/bro...sing-Coil.html
Cheaper models new and used can be had on the Bay..

[kx250rider]

It shouldn't be "damaged" at all. Not unless, that is, you used one of those magnets that they have at the junk yard to hoist wrecked cars into the crusher...

As the others said, you just need to degauss the tube. I've used a Weller soldering iron in a pinch, but the best is a degaussing ring. Before doing any of that, use the built-in coil by cycling the TV on & off several times, waiting 15 minutes "OFF" for the degaussing thermistor to cool off so as to reactivate the coil when you turn the set back on. (If you don't wait for the TV to cool, the coil won't cycle on because the thermistor will stay open) I say it will be fine.

Charles

[lguise]

it fixed itself. i had a pair of woofers on the floor under the tv. though they were at least 3 feet away, i had a green screen at the bottom. thanks for all the great tips!

[avionic]

Originally Posted by lguise

it fixed itself. i had a pair of woofers on the floor under the tv. though they were at least 3 feet away, i had a green screen at the bottom. thanks for all the great tips!

Unshielded speakers will do it every time...

[Dave S]

I was taught by the old TV repairman at the shop where I worked after school in the sixties that the built-in degaussers aren't as strong as the outboard units. They're just meant to provide routine "maintenance" or "touch up" degaussing.

"Real" degaussing coils show up every now and then at swapmeets and on eBay. Sounds like you could use one. I might have an extra one here. I have one set that's either so magnetized or somehow otherwise damaged that even multiple treatments with an external coil wouldn't get it back into line. I'd love to find out how that happened.

--Dave

[avionic]

I have one set that's either so magnetized or somehow otherwise damaged that even multiple treatments with an external coil wouldn't get it back into line. I'd love to find out how that happened.

A loose shadow mask within the CRT will really foul up the purity and look similar to a magnetized screen.

[marty59]

Maybe the yoke has slid back a bit and needs repositioned.

[jeyurkon]

Originally Posted by avionic

A loose shadow mask within the CRT will really foul up the purity and look similar to a magnetized screen.

The mask is ferromagnetic. With a strong magnet it can be distorted. Or, what you said.

John

[Jeffhs]

My RCA XL-100 CTC185 fell off its stand a few months ago. When I put it back and turned it back on, I saw splotches of color on the CRT screen. The automatic degaussing coil in the set was no help, though it did cycle on and off as it should when the set was turned on. Wondered what was going on for a few days, then I tried moving a speaker magnet around the screen, while the set was on. To my surprise, the splotches disappeared and did not return. The picture now looks every bit as good as the day I bought the set, nine years ago. I mentioned this in a thread on this forum shortly thereafter, and got a reply (among several others) to the effect that the shadow mask may have been bent when the TV hit the (carpeted) floor in my apartment; the external magnet may have repositioned the mask such that it was now back in proper alignment.

[julianburke]

In the past I have seen a few sets that had a warped shadow mask. Possibly by falling hard on their face but had a purity problem that could not be cured. I saw one once that had a loose mask too. (you could hear it when moving tube) Very rare but still possible. Most purity problems can easily be cured with a good degaussing.