That is actually caused by the earth's magnetic field. I actually read in the Sony Trinitron's service manual that you need to face the TV in an east or west direction when dialing convergence to reduce the earth's magnetic interference.

(Useful information for CRT owners here btw. Bookmark this)

April 08, 2026 - 05:44 UTC

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Yep, found this out first hand when I got my first arcade cab. Found I could rotate the monitor so I did, because I'd also picked up a TMNT* board with my vertical cab and the screen went... well, you know.

Eventually got it right!

*Teenage Mutant Hero Turtles because the BBC disliked 'ninja'
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That's awesome lol. I forgot that they called it Hero Turtles in Europe, that is crazy haha.
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nothing feels closer to "Humans toying with eldritch and ancient magic" like crt televisions. "yeah you need to face it east or the magnetic pull of the planet will interfere with it. Also if there's no signal it'll pick up on signals left from the birth of the universe."
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I had no idea of any of this. I feel very ignorant lol.
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Thank you!!!
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I've had this tweet saved for a while because it's also extremely useful information for convergence.

Permalloy strips, for those who don't know, are little magnetic stickers that you put behind the deflection yoke and they fix mismatched convergence in the corners which is a common problem.
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I must also add that you can get zapped by this because these adjustments must be made with the screen on, so be careful. Don't touch the anode cap or the flyback or the red wire between them. Always use one hand to keep a charge from going through your heart, and wear some gloves.
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Bit like when the early colour TVs had to be 'professionallty installed' as the early shadow mask tubes were extremely sensitive to external magnetic influences like the earth's field.
The convergence had to be adjusted 'in situ' ,and if they were moved, even slightly, it all had to be done again.
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When my old BVM-20E1U still lived, this was a thing I had to worry about. It takes like a month after being moved to fully settle in with the surround magnetosphere and shit, CRTs are nuts.
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If you unplug the TV for a handful of minutes before rotating and powering back on, that may be enough to prevent discoloration.
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