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From: bender@oobleck.Eng.Sun.COM (Michael Bender)
Newsgroups: sci.electronics
Subject: Re: sort of fixed monitor
Message-ID: <2353@exodus.Eng.Sun.COM>
Date: 8 Nov 90 04:35:25 GMT
References: <1990Nov6.233222.8908@nntp-server.caltech.edu> <2262@exodus.Eng.Sun.COM> <1990Nov7.230205.2520@rand.org>
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Organization: Sun Microsystems, Mt. View, Ca.
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In article <1990Nov7.230205.2520@rand.org> edhall@rand.org (Ed Hall) writes:
..>In article <2262@exodus.Eng.Sun.COM> bender@oobleck.Eng.Sun.COM (Michael Bender) writes:
..>>In article <1990Nov6.233222.8908@nntp-server.caltech.edu> gwoho@nntp-server.caltech.edu (g liu) writes:
..>>> . . . .
..>>>this is wat it was for: when the computer is turned on, the resistor
..>>>is cold, so it lets lots of current go through a coil that is in front
..>>>of the crt. after 1 sec, it gets hot, and the current shrinks, and it
..>>>demagnitizes the metal chunks around the crt.
..>>I can't help with the scratch, but for the resistor, you could try
..>>substituting a momentary push button switch, optionally with a fixed-value
..>>resistor in series with the switch if the miniumum reistance of the original
..>>resistor was much greater than a few ohms.
..>
..>Don't do this!  There is a reason why they used that particular mechanism.
..>The current through the coil must be reduced *gradually* or else it might
..>wind up making matters worse (i.e. instead of a DEmagnetizer it would
..>become a magnetizer.)  It shouldn't be too hard to find a replacement
..>thermistor; just about all high-quality CRT's (and even TV sets) use
..>a similar mechanism.
..>
..>		-Ed Hall
..>		edhall@rand.org

you're right - my friend Jeff warned me about this last night on the phone
after I told him what I posted.  you could always do a high-tech degausser,
using one of the uP's that we've been talking about on the net for a few
weeks and a D/A converter and a power amp; that way, you could have a
virtually unlimited type of ramp-down.  maybe you could even add a
hall-effect sensor to the circuit so that if the ambient magnetic field got
strong enough past a (user-defined) threshold, the uP would power up the
degausser.

mike

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