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"I'm having problem(s) with a brand new 40" Mitsubishi tube (direct view) TV. I'm writing this with hopes of getting some basic information so that the dealer doesn't bamboozle me.From first viewing (5 minutes after the delivery man departed). I noticed a discoloration patch in the top right hand corner (purple when the background is blue/greenish when background is white)."
(From: Tony (ard12@eng.cam.ac.uk).)
As you probably know, a colour TV produces a red picture, a green picture and a blue picture on the screen at the same time. You eyes interpret that as a coloured picture. If you look at (a normal, non-projection) TV screen through a magnifying lens, you should be able to see red, green and blue dots, and no other colours.
Now, there are 3 basic adjustments to getting a good colour picture :
(From: VK.)
"I called the store in a panic and they calmly told me to press the "degauss" button to eliminate the problem (which I quickly learned was spurious magnetization, caused perhaps by storage near a speaker in the warehouse?). Result? Better but not cured."
(From: Tony.)
Yes, spurious magnetization (or more correctly a different magnetic field around the tube from the one present when it was set up) will cause purity problems.
(From: V. K.)
"The next day I visited the store, and the manager said (again) that this was an easily fixable problem, requiring a few waves of a degaussing coil. To appease me, he sends the salesman home with me with small (1 foot diameter) coil in tow. Salesman (boy, actually) waves the coil in front of and around set but can't seem to remove the discoloration."
(From: Tony.)
Argh... Here's what should have been done IMHO.
Note that convergence and purity interact to some extent, and thus if either is adjusted, both must be checked (and rechecked). Grey scale adjustments interact with nothing else.
I would want to see the set on a pattern generator (at least the patterns I've mentioned above) and identify the problems.
(From: V. K.)
"To demagnetize the TV, he says that a large coil is required, that encompasses the whole unit; service rep will 'be in touch'."
(From: Tony.)
I've never heard of that - the correct procedure is to wipe the coil around the front, top, sides and bottom _NOT the back_ and then move it 2-3m from the set before turning it off. It doesn't matter whether the set is on or off for this, btw. I've not heard of putting a large coil round the entire set. (See the section: Degaussing (demagnetizing) a CRT.
(From: V. K.)
"After the sales boy leaves, I could SWEAR that the picture quality in general is decreased, with people (especially their extremities like lips and ears) appearing pinker than before, and also more general interference (fringes/noise) noticeable."
The convergence and purity are set by ring magnets on the neck of the tube. It's possible that the degaussing procedure has slightly demagnetized these, and if so, the whole set will need to be set up. Similarly, if any part of the set was magnetized at the factory, then the adjustments may have been set up to compensate, and then after demagnetization, they'll need to be reset.
(From: V. K.)
"So my questions are these. Can the original problem truly be FIXED with proper sized coil and application?
(From: Tony.)
I don't think the size of the coil will make any difference. I would want to see that set on a pattern generator, so I could be _sure_ as to what the problems are. If the dealers don't have a pattern generator, then they're not fit to be fixing TVs IMHO.
(From: V. K.)
"Could I be imagining that the waving of the small coil degraded the picture quality?"
(From: Tony.)
It's possible, but fairly unlikely. See above
(From: V. K.)
"Should I demand replacement to a new set? Can I legally ask for this, or is it like a new car...you own it, now you deal with the service guys forever.
(From: Tony.)
I don't know US law, but in the UK, if a product is defective, you can demand a refund of the money paid (not a replacement or a repair, a refund). IMHO, a TV with incorrect colours is defective...