How did analog color televisions "fix" alignment problems in three-gun systems?

Question

I recall my grandfather panicking when I attempted to adjust the tint on his TV. He said that he would have to call the TV people to come and re-align it. I thought he was crazy at the time, but later learned this was a very real problem in early color televisions, and that getting the three guns to align on the screen properly was apparently something of a task.

So...

is this true? I assume with a one-gun system like Trinitron this wasn't an issue in the first place, but even with a delta it's not entirely clear to me what the issue is - one gun not passing through the focus of the deflection system?
how did they fix it? I certainly don't recall any TV from, say, 1980 on having these sorts of issues or any controls for addressing them. This suggests there was either some way of eliminating the effect entirely, or perhaps an auto-adjustment system

@periblepsis - it does. It appears it is all done through measuring currents from each of the guns (in turn one assumes) hitting the shadow mask. Now I see it, the minimum current point is the point of best beam position. And look at all those tubes! — Maury Markowitz, Mar 01 '23 at 01:31
@Maury It was the best I could find for you at the time. I'm glad it helped out. :) — periblepsis, Mar 01 '23 at 05:36

score 0 · Answer 1 · answered Feb 28 '23 at 19:17

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Old TV’s had more errors to correct and it was difficult to balance magnetic focus, pin-cushion correction, blooming brightness and saturation, color balance and gamma non-linear effects with variable image content.

Having tubes with heat caused some sets could also drift.

Modern sets are normalized to stabilize tint and saturation with changes in brightness = offset and contrast = gain.

Being an engineering student gives you an advantage by understanding how to control effects for your personal choices. But he who had to pay a couple hundred dollars in the past to fix the color might have a reason to over-react or be cautious. ;)

answered Feb 28 '23 at 19:17

Hoagie

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Modern sets are normalized to stabilize tint and saturation - OK, but HOW. In order to fix a problem you need to measure that problem, how does a TV actually perform the measurement and feed that back into the controls? – Maury Markowitz Mar 01 '23 at 01:29
This 10 page answer might fulfill your curiosity. @mau http://www.hawestv.com/mtv_color/colrtel_enhance.htm – Hoagie Mar 01 '23 at 15:58

score 0 · Answer 2 · answered Feb 28 '23 at 19:22

The term you are after is convergence.

And it is not typically a problem that needs fixing.

It is aligned by adjusting convergence rings on the neck of the CRT. They are basically adjustable magnets, maybe accompanied by coils if there is an electrical adjustment.

A Trinitron still has three beams but packed more densely into single package.

Convergence is typically not an user adjustable operation, at least not unless the convergence system has coils and some kind of menu to adjust it - could be some kind of service menu instead of standard user menu.

When convergence is adjusted, there is typically no reason why it would go out of alignment in normal use, so it typically does not need any further adjustment.

There can also be no auto-adjustment as the monitor obviously can't know how the picture looks like.

"Convergence" is the correct term, but the ring magnets on the neck of the tube only controlled static convergence at the center of the screen. There was also dynamic convergence to deal with the effects of scanning, and this involved a long process of adjusting a dozen or more controls that all interacted with each other in strange and wonderful ways to get convergence at the sides and corners of the screen. — Dave Tweed, Feb 28 '23 at 20:13

How did analog color televisions "fix" alignment problems in three-gun systems?

2 Answers2