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From: akers@oliven.UUCP (Rob Akers)
Newsgroups: net.video
Subject: Magnetic fields and Color TV Warning/Questions
Message-ID: <499@oliven.UUCP>
Date: Tue, 28-Jan-86 14:19:24 EST
Article-I.D.: oliven.499
Posted: Tue Jan 28 14:19:24 1986
Date-Received: Sat, 1-Feb-86 02:33:25 EST
Organization: Olivetti ATC; Cupertino, Ca
Lines: 46

During the Superbowl we had two color tv's on, one to watch the game and
the other to act as a monitor for the VCR which was recording the game.
Watching two sets was distracting, so I placed a box (which happened to
contain two small loudspeakers) directly against one screen to block the
picture.  I removed the box after about 30 seconds and found that the color
on the set had changed drastically.  There were now 3 horizontal "zones"
of color on the screen.  The top zone had an overwhelming red tint, the
middle zone had an overwhelming blue tint, and the bottom zone had an 
overwhelming green tint.  Thinking I had possibly knocked the antenna
loose I checked the connections but they were fine.  Adjusting the antenna
and the tint control did not correct the problem. I continued to watch the
set for about 15 minutes; the zones of color remained during this time.
I turned the set off for a few minutes, turned it back on and the problem
still existed.  By this time I was concerned that the set had been permanently
damaged, and I still didn't understand what had happened.  I moved the
box containing the speakers in front of the set, and the zones of color 
became much more intense.  I turned the set off for about 30 minutes.
When I turned it back on, the picture was fine.(thankfully!)

Apparently the magnetic field from the speakers had caused the problem.
There are two things I don't understand:

1) Why did the problem remain for so long (15 minutes) after the speakers
were moved (far away) from the set?  Is the picture tube capable of holding
a magnetic charge?  Is there metal sheilding around the tube which could
hold a magnetic charge?  Could this permanently damage the picture tube?

2) Why did the magnetic field cause the distinct red, blue, and green
zones to appear?  Is there a relationship between color (frequency ?)
and the amount of deflection from the magnetic field?  Is it related
to the distance of the gun(s) or lens(es) from the magnetic field?


Excuse the dumb questions, but physics was a long time ago and I am
fairly ignorant of the inner workings of a color television set.
Recommendations of good books on the subject would be appreciated.

The set is a 19 inch Toshiba, about two years old.


Any ideas or commments out there?


Thanks in advance,

Rob Akers