Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!sdd.hp.com!hplabs!hpl-opus!hpnmdla!hpsad!frankb
From: frankb@hpsad.HP.COM (Frank Ball)
Newsgroups: sci.electronics
Subject: Re: TV Picture Tubes and Speaker Magnets
Message-ID: <1840052@hpsad.HP.COM>
Date: 25 Jun 91 15:28:57 GMT
References: <1991Jun12.192427.18120@syssoft.com>
Organization: HP Signal Analysis Division - Rohnert Park, CA
Lines: 24

/ clemon@lemsys.UUCP (Craig Lemon) /  6:51 am  Jun 24, 1991 /
        *I think we got away from the point for a second or two here.  The
*answer I was waiting for was to the question "Does this operating
*environment damage the CRT?".  Sometime I'm inclined to set a muffin fan
*(why do they call them "muffin" fans ? :-) on top of my montior (NEC
*Multisync IIA) as it gets quite warm after a while and cool is always better
*(usually :).  When I do this I can notice a slight (_slight_) rippling
*effect in the picture if I look hard.  I want to be sure that prolonged
*exposure to a magnetic field will not mess up my convergence or anything
*like that.  I'm not sure whether the IIA degausses on power-up.  Does
*anyone else know?

Color TVs do degausse the tube on power-up, but they will only degausse
a mild magnetization on the grid (I think its called a grid, its a metal
plate full of little holes just behind the glass faceplate of the CRT).
When this plate gets magetized it bends the paths of the electrons and
distorts the picture, the colors get really strange.  If you get a strong
enough magetization on the grid the degausse coil built into the set will
not do the job.  It is possible to do it with a handheld AC electromagnet,
but it is very difficult to do a good job.  I would avoid anything that
causes visible distortion on the screen, it is asking for trouble.


Frank Ball   frankb@hpsad.HP.COM   pyramid!hplabs!hpsad!frankb