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From: myers@hpfcrlm.HP.COM (Bob Myers)
Newsgroups: sci.electronics
Subject: Re: TV Picture Tubes and Speaker Magnets
Message-ID: <17660179@hpfcrlm.HP.COM>
Date: 26 Jun 91 17:45:32 GMT
References: <1991Jun12.192427.18120@syssoft.com>
Organization: Hewlett Packard -- Fort Collins, CO
Lines: 23

>(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?

I don't know for sure whether the IIA degausses on power-up or not (you could
tell by listening for an "AC power"-sort of hum for a few seconds when the
monitor is powered up, after having been off for a minute or so).  In any
event, you're not likely to have convergence problems as the result of putting
an *AC* fan on top of the display; the rippling you're seeing is just the
AC field from the fan mucking around and beating with the deflection (the
vertical deflection of the display is NOT locked to the line), and, since it's
an AC field, it will not wind up magnetizing the tube structures (such as the
shadow mask) and thereby cause purity and convergence problems.  Even if it
DID, degaussing the monitor is no big deal.  You SHOULD always look for a
monitor with built-in degaussing (auto or manual), but even those are likely
to eventually need a pass with an external degaussing coil to keep things OK.


Bob Myers  KC0EW   HP Graphics Tech. Div.|  Opinions expressed here are not
                   Ft. Collins, Colorado |  those of my employer or any other
myers@fc.hp.com                          |  sentient life-form on this planet.