Electric fans and my monitor

This seems like a question that should have been asked by now, but I can’t find it anywhere. It’s darn hot in my dorm room, and I would like to position my electric fan to blow on me while I sleep, so I place it on my desk right next to my computer monitor. Now, I know that strong electric motors have an adverse effect on televisions - after having an electric pencil sharpener next to the TV for a couple of years, the corner of the TV turned permanently green or purple or something. And when I put the fan next to the monitor, there’s no question about it - the display flutters. Badly. I assume this means that it hurts the monitor, and that if I keep it up, the display will be permanently distorted. Is this true?

Also, I have been naively turning off my monitor at night and setting the fan on full blast next to it, thinking that if I can’t see the distortion, no harm is being done. Is this true?

The “flutter” is caused by the magnets in the electric motor interfering with the electron stream in the monitor which produces the picture. If it’s off (the monitor, that is), there shouldn’t be a problem, as there is no stream. As for permanently ruining the monitor by running the fan when close-by when the monitor is on, this most likely won’t be a problem, either. You can probably just degauss it (most monitors either come with an on-screen control or a button control to accomplish this) to fix any “left-over” distortion.

Great. Thank you for putting my mind at ease - I can now rest in peace. I had realized (i.e. assumed) that it was due to the magnetic field of the motor, since I get a purple or green discoloration when I hold magnets up to monitors. However, I have another question. I know someone who held a medium-strength toy magnet against a monitor for an extended period, about 10 minutes. The discoloration stuck after that. It faded over time, but I could still make it out several months after the incident. I find it hard to believe that this was only because nobody degaussed it in all that time. However, I can’t actually testify that it was ever degaussed, and this was an older screen, so it’s possible it didn’t have that option. Are magnets really unable to cause any problems that degaussing can’t fix?

You’re actually describing two different effects, Achernar, the fluttering and the discoloration.

The fluttering is caused by the electric fields from the fan deflecting the electron beam in your monitor’s CRT. A CRT works by generating a beam of electrons that draws patterns on a phosphor coating on the inside of the face of the tube. The beam is steered by two pairs of plates that create electric fields, one pair for horizontal and one pair for vertical. When you put your fan next to your monitor, its motor’s electric fields are also “steering” the electron beam, thus causing the picture to “flutter.”

The discoloration of the picture is caused by changes in the phosphor coating induced by a strong magnetic field. I’m not clear on exactly what changes happen, or why it causes the color to change, but perhaps someone else can explain this detail.

You can see this effect by holding a horseshoe magnet near the front of a TV or monitor. Briefly. In fact, you may want to use someone else’s TV. While the magnet is close, you will see vivid changes in the way the phosphors represent color, and a small persistent effect will remain when you remove the magnet.

I used to keep my VCR on top of my TV until I noticed that the transformer in the VCR’s power supply was affecting the color in the top left corner of the TV. I’ve moved the VCR, but there’s still a bluish tinge on that corner.

Bottom line is that if you can’t see any discoloration in your monitor, then you’re not doing any permanent harm to it.

The fluttering is not a permanent effect, and is completely harmless. To your monitor. Watching it may give you headaches, though.

The metallic shadow mask (or aperture grille used in some CRTs) can become magnetized by strong magnetic fields such as bughunter’s horseshoe magnet. The job of the shadow mask is to make sure that the electron beam falls perfectly on the correct phosphor dot. To do this, the shadow mask’s grillwork and the phosphor dots must stay perfectly aligned relative to one another and therefore the shadow mask must be made of a metal that has the same thermal expansion characteristics as glass. The only practical choice for the shadow mask is Invar metal, an alloy that unfortunately is easily magnetized.

When the shadow mask has become magnetized, the the electron beams in your television are being steered in wrong directions by the magnetized shadow mask so that they hit the wrong phosphors. That’s why you see color splotches.

Modern TV sets have automatic degaussing which is supposed to dispell very slight magnetic fields. Stronger fields from, say, horseshoe magnets, will have to be manually nullified with a device called a degaussing coil.

Degaussing coils are available in two different sizes, and are a lot cheaper than they were when I was working on consumer electronics:

Degaussing coils (If that link doesn’t take you directly to the items, just do a search for “degaussing coil”)

If you use a low-voltage DC powered fan you can get rid
of the flickering…I have DC powered fans sitting directly
on top of my monitors (to help keep them cooler because it
gets hot in my room) and have no problems at all with
flickering or discoloration (most DC fans do not create
a large electro-magnetic field like standard AC ones do).

your current fan should be ok as long as the monitor is off
when the fan is on…but keep it away from your computer
because there is a chance of corrupting data on the