Originally Posted by FunHouse Austin
magnetic damage can be permanent
It can often be fixed, although in some cases the damage will continue to appear until fixed.
I used to have a Sharp tube that we had in a corner of an apartment living room, apparently too close to a wall-mounted air conditioner unit. The upper corner of the TV was always dark as a result, even when moved away from the AC. I figure the magnet in the compressor motor caused the gauss effect. I never did try to fix it (didn't care that much, really).
Years ago when I worked at an electronics retailer's service counter, we had a homemade degausser that the techs used to use to fix magnetic damage. It was really nothing more than an electromagnet (about a one foot diameter coil of wire, wrapped in electrical tape, an plugged into a wall outlet) that the techs would wave around a tube until it looked better. We used to play with it on the CRT monitors for the inventory/mainframe system, although the techs would yell at us. But we never caused any permanent damage. And it looked cool. It's amazing what can count as "fun" to bored teenagers at a part time job.
Some CRT TVs degauss when power-cycled. Some CRT PC monitors have a "degauss" button which can fix magnetic damage when pressed. Otherwise, an external degausser is the best way to fix the damage.
In many cases, the damage is not permanent.