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From: yjwu@unix.cie.rpi.edu (Yeun-Jung Wu)
Newsgroups: sci.electronics
Subject: Re: TV degauss problem
Message-ID: <6978@rpi.edu>
Date: 29 Aug 89 16:57:14 GMT
Sender: usenet@rpi.edu
Reply-To: yjwu@unix.cie.rpi.edu.UUCP (Yeun-Jung Wu)
Distribution: sci.electronis
Organization: CIE, Rensselaer Polytechnic Institute, Troy, NY
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	I got several good recommendations since last Saturday. I am 
pretty much sure now that the problem is due to the permanent
magnetization of the shadow mask. The manufacturers do not use aluminum 
for the mask material probably because it is not mechanically strong 
enough to support the fine pattern and they do not need nonmagnetic stainless
steel neither because it is in a vacuum seal and its high cost. 
	So what I need is a degaussing coil which is a coil with A.C. current
passed through, I guess. I remembered that long times ago my dad had one 
such coil to demagnetize screwdrivers and many other tools. Right now I have 
a induction motor from a cheap turntable. I can take the rotor away but the
effective area is a little bit smaller and to cover the whole screen will take
me a long time. 
	Last night I gave my TV set a heavy dose of static magnetic field 
(that magnet again) but I tried my effort to smear it more uniformly 
out through the whole screen. I really screwed up at some time and the screen
went crazy; it looked like the spectacular sky in the north pole during the
active sun spot period. But finally it is much better than before; the non-
uniformity is quite invisible if it is not under the white background. 
I adjusted the purity rings on the neck to make sure that the letters in text
mode of my Apple ][+ is convergent on most of the screen. (I only adjusted 
one pair of them and I marked where their original positions are.)
	The accident give me a good lesson and I do learn a lot from all of 
you. Thank you for your suggestions and effort.