What I learned fiddling with CRT magnets...

[smrieck511]

Just don't do it.

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[zigzagjoe]

Just don't do it.

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Amen to that. Unless something is radically off.... you're equaly likely to mess things up than improve them. At least, that has been my experience.

 

[smrieck511]

I got pretty close… But never enough to stop messing with it... after about three weeks I broke down and just bought a new yoke.

 

[s_pupp]

Ten of my 11 compact Macs have significant geometric abnormalities, as do the half-dozen CRTs-with-yoke that I have bought looking for something acceptable. After failing to make an improvement with any of them, I purchased a new old stock Clinton tube for quite a price. It arrived with one of the magnets lying loose in the box.

I don’t understand all these undistorted tubes I see in pictures here and on eBay. The only one I’ve seen is the second SE/30 I bought, which was 20 years ago. Even the Mac Plus I bought in ‘86 has a distorted screen.

 

[mg.man]

I got pretty close… after about three weeks I broke down

I've had pretty good luck on the few I've needed to "straighten" out. It is a mind-bender, though, with each magnet affecting the others nearby.

I wonder if many of the badly off ones you find on the various marketplaces are the result of "frankenstein" reconstructions?

 

[joshc]

The only thing I've noticed where magnet adjustment would be needed is when you get skewed corners - most noticeable on the menubar edges. Is that what others have mostly experienced as well? I've never tried to rectify this, always just put up with it instead.

 

[Phipli]

I have one slightly wonky SE, and an iMac I can't quite get right, but the latter might bust be me, everything else is fine.

I have more CRTs with burn-in than wonky magnets.

 

[smrieck511]

if there weren't high-voltage involved, it would actually be a sort of fun game.

 

[Skate323k137]

You mean convergence rings, or the actual magnets for corner convergence?

I loathe touching the rings, but I don't mind sticking a permalloy strip or two around the yoke to fix corners.

 

[smrieck511]

You mean convergence rings, or the actual magnets for corner convergence?

I loathe touching the rings, but I don't mind sticking a permalloy strip or two around the yoke to fix corners.

The actual magnets which are sealed with a little paint of some kind.

 

[joshc]

I loathe touching the rings, but I don't mind sticking a permalloy strip or two around the yoke to fix corners.

What's the trick here? Can you explain it in more detail please? Haven't heard of this as a fix for skewed corners before.

 

[Skate323k137]

What's the trick here? Can you explain it in more detail please? Haven't heard of this as a fix for skewed corners before.

I can't speak to how well it would work on specific Mac monitors, but arcade monitors 25" and over almost always have corners with the colors out of convergence. This is the concept demonstrated, and the same method I use. I always have a 2nd person for safety and I trust their eyes when they tell me the tab is good (as I'm behind the monitor) or have them hold a mirror so I can see the corner while positioning the strip.

The actual magnets which are sealed with a little paint of some kind.

It's normal for a paint mark to be drawn down the convergence rings. Usually for a reference point. And yeah, I don't like messing with them either.

 

[4seasonphoto]

Even if you could tweak to perfection, when you move the computer to a different geographical location, it's probably going to be off again because that stuff is affected by the earth's magnetic field. Some late CRT-era monitors had great controls for adjusting geometry, which could all be done via buttons on the front panel.

 

[Fred1212]

I've swapped a number of crt's around between SE, SE/30, classics and you need to fiddle with the convergence rings and the small magnets to get them right. It's not hard and luckily I've never been bitten by the HV. Best to use just one hand to be sure of avoiding the HV. It does take a bit of time as the small magnets affect each other and also the convergence.

 

[ObeyDaleks]

Personally I have had pretty good success with adjusting the little magnets on two of my compacts. They both had the same problem - top and bottom not being parallel, forming an ugly sideways trapezoid. I did have one that I couldn’t fix no matter what I did so I just bought another yoke. All my compacts now have a perfect rectangle dead center.

 

[s_pupp]

I've swapped a number of crt's around between SE, SE/30, classics and you need to fiddle with the convergence rings and the small magnets to get them right. It's not hard and luckily I've never been bitten by the HV. Best to use just one hand to be sure of avoiding the HV. It does take a bit of time as the small magnets affect each other and also the convergence.

Personally I have had pretty good success with adjusting the little magnets on two of my compacts. They both had the same problem - top and bottom not being parallel, forming an ugly sideways trapezoid. I did have one that I couldn’t fix no matter what I did so I just bought another yoke. All my compacts now have a perfect rectangle dead center.

I'm very impressed by your patience and resulting success adjusting these magnets. It is because of the magnet fiddling that I've been dreading getting back to the SE/30's for the past 10 years.

 

[mg.man]

patience and resulting success

That's exactly it... patience (and persistence) and I've usually been able to get good results. It's also a case of the more you do, the more you get the hang of it. It's a bit of a black art, but worth it IMO.