Hacker News Reader

Comment by kamilner | Hacker News Reader

There's a throwaway comment in here about the earth's magnetic field affecting CRTs and turning the TV upside down, is that actually true? I would have thought the earth's magnetic field would be incredibly weak in comparison to the deflecting coils.

View on HN

I've had TVs move room to room and face a different direction and need to be fixed with a degaussing coil. I'm told it's from the Earth's magnetic field. Could also be that they were next to other TVs (arcade machines in this case).

If i had to guess, i bet it's the other machines nearby. I'm sure we've all felt the static from a crt screen when it's turned off. Being in a closed room of turned on crt's would probably create a significant field of potentials around the room. I can't imagine the earth's magnetic field is so erratic as to change noticeably from room to room. I'd think any variation of that order would disrupt the functioning of compasses, and the phenomena couldn't just be localized to your one room on earth, compasses would be somewhat unreliable all over the globe then.

But who knows, maybe a solar flair hit you between rooms and changed the environment enough to disrupt the tv, but then i'd bet it'd effect all the machines. Eh, who knows. Weird thing that electromagnetism

Aurora Borealis? At this time of year, at this time of day, in this part of the country, localized entirely within your kitchen?!

I've got a cocktail video game, and the top (which the screen is mounted to) is on a hinge. There's a decent degauss on start, so if you start it with the screen up, it's fine, and if you start it with the screen down, it's fine, but if you move it while it's on, the colors get weird.

Rotation can affect image purity. You don't even have to turn the set upside down. If you have a set that already has some color purity issues due to bad magnetism of the mask, you can affect that (and sometimes even find a position that eliminates it) simply by rotating the TV around on the surface it rests on.

I just sent an email to my old high school buddy. I'm sure this is incorrect, and I've asked him for his remembrance of something we did on a lark.

One night David Letterman did an episode where throughout the show, the camera(s) did a full 360 degree revolution.

When the show was half-way through, it was of course, upside down. So we turned the television upside down.

I personally don't remember anything unusual about the way the show appeared, other than that the TV was upside down, and then on its side for a few minutes at the 45 minute mark.

If he responds within a reasonable time, I'll follow up to mention if he remembers this the same way I do.

People frequently rotate CRTs for arcade games. They're fine.

Actually, this is a perfectly good point - arcade games had their CRTs on a 45 degree angle, some on portrait and some on landscape direction, and they showed no "intermediate" effects that you'd expect if this gravity claim was true. There were even "table" video games where the CRT was 90 degrees upward, which should have really messed things up if this gravitational effect was at all true.

Likewise, remember the green swooping radar of days gone by? In wartime, those regularly got a wild ride through gravity, and yet you never hear of them having a problem with it.

I'm really thinking this article's "throw-away" comment is really worth throwing away.

> Likewise, remember the green swooping radar of days gone by

Monochrome CRTs don't have a shadow mask or an aperture grille, and no degausing or need for it. Certainly, magnetic fields will interact with the electron beam of a monochrome CRT, but if it's the earth's magnetic field, it will be uniform over the whole screen, and not a big deal.

They most likely also degauss the tube while in the vertical orientation.

I've never needed to. Just tried it and didn't make any perceivable difference.

Correct, the field of the Earth is weak and won’t mess up the image on the TV.

Incorrect.

The earth's magnetic field definitely affects Cathode Ray Tubes and many other things.

High end CRT computer monitors came with a built in degaussing system and some had controls for aligning the R,G & B electron beams.

https://en.wikipedia.org/wiki/Degaussing https://hackaday.com/2016/05/25/wtf-is-degaussing/

From personal experience, I took a 20" Sony Trinitron from Los Angeles to New Zealand in the mid 90's. the reversal in the Earth's magnetic field between the northern and southern hemisphere's meant I could never completely get the RGB guns to line up correctly.

https://www.webopedia.com/insights/monitorhemispheres/

I used to move 20-inch CRTs around in the office and have to degauss them. But stationary ones also needed this and the built-in coil was great.

I'm more inclined to blame that on the buzzy neon tube lights overhead, and the computers sitting under them.

To me, this sounds a lot like the directional flow of toilets flushing. I'd have to see this as an actual experiment before I can be convinced of what the webopedia page is claiming.

Check out my previous comment on the time a friend and I watch his TV upside down. There was zero difference that I remember.

Consider where most of the monitors are shipped from. Did they send "southern hemisphere" specific televisions and crt monitors? And what happens at the equator?

Could your monitor have been fritzed on the flight? Did it work normally when you brought it back?

This would actually be a fantastic YouTube video, whether it debunks or proves the claim being equally interesting.

This is simply not true. If it were, then a monitor at the equator would be ruined merely by rotating it to face east instead of west, or north instead of south. They would have needed to sell four different monitors, to accommodate customers who were going to face their monitors in different directions. Even away from the equator most of the magnetic field points north/south rather than into or away from the Earth. More likely vibration during shipping defocused your monitor somewhat; a TV–repair shop probably could have fixed it.

It's much more likely that your TV suffered in-transit knocks and bumps that rendered it out of alignment, and too out of alignment to be able to be re-aligned.

Some professional Sony BWM series monitors have menu settings for the direction where the monitor is facing to compensate for the earth magnetic field.

Reply on news.ycombinator.com