Path: utzoo!attcan!uunet!ginosko!gem.mps.ohio-state.edu!rpi!unix.cie.rpi.edu!yjwu
From: yjwu@unix.cie.rpi.edu (Yeun-Jung Wu)
Newsgroups: sci.electronics
Subject: TV degauss problem
Message-ID: <6939@rpi.edu>
Date: 26 Aug 89 14:01:52 GMT
Sender: usenet@rpi.edu
Reply-To: yjwu@unix.cie.rpi.edu.UUCP (Yeun-Jung Wu)
Distribution: sci.electronics
Organization: CIE, Rensselaer Polytechnic Institute, Troy, NY
Lines: 39


	I got a Toshiba 20" stereo TV eight monthes ago. It works fine until
recently that a huge purple spot appeared on the screen. It happened when I 
took a magnet near the screen to see the effect of magnetic field on electron
trajectory. I know that the TV set had a problem of slow recovering from 
the change of earth magnetic field when I moved it from place to place. 
Last time I wanted to use the sheet metal cabinet on which I put my TV set. 
So I moved my TV set somewhere. When I put it back to its place and switched
it on, one quarter of the screen on the right turned purple. I knew that 
probably I have to wait a long time to let the "degauss" circuit to work but
I was not patient enough. Then I took a magnet (a ring magnet from raw speaker)
to see whether I can wake it up by subjecting it to weird magnetic field.
I saw the pretty pattern on the screen and tried rotating the magnet to see
its effect. From my previous experience I know that I can't play it too long.
So the screen ended up with the purple part and some dipole pattern. That 
purple part on the right of the screen faded away gradually but a huge purple
spot remained on it forever. I know that I can "cancel" the spot by 
positioning the magnet near screen with some angle but it seemed stupid to 
have a magnet in front of the TV set to make it work properly. 
	How does the "degauss" circuit work? Dose it take into consideration
that the set will experience different component of earth magnetic field when
we orient it differently? 
	This problem got me pretty upset so I decided to open the case to see
what I can do. I cannot locate the "degauss" circuit because there are only 
wires go to the vertical and horizontal scanning coils and I did not see any
part of the PCB marked as "degauss" section. I adjusted some of the small 
magnets near the electron guns. The situation get better and there is a smaller
"green" hue spot near the upper center now. It is not that bad and only shows
up when there is a uniform background. Right now I am using my Apple ][+ to 
generate a white background to optimize the balance. But how comes that I have
to adjust those magnets? 
	I appreciate any opinion concerning this mystery. Please forward your
mails to my mbox. E-mail address follows as
        
	yjwu@unix.cie.rpi.edu

	Thank you for your patient with my poor English!