A Sony' CRTs color is screwed up.

[Arfa Daily]

"John-Del" <ohger1s@aol.com> wrote in message
news:13a1ddf4-2b1d-4c6f-a3cb-efd34f7c72a6@googlegroups.com...

On Sunday, June 2, 2013 1:15:58 PM UTC-4, Smarty wrote:


I have not dealt at all with magnetized Trinitrons / aperture grills,

and only have very limited experience with magnetized conventional CRTs

but purity problems certainly were visible in the black and white images

of those needing degaussing. It did not take moving color images to

suggest purity / magnetization nor did it take careful inspection.


Perhaps your experience is with the old delta gun arrangement, which were
prone to more purity error and more severe error. But I can tell you that
with modern in line arrangements (Sony being no exception), bad purity is
not always obvious in black and white pictures.

+1 - see below

The

other, even more confusing original post issue was the non stationary

nature of the color shifts, and the fact they were reported as moving

with the displayed image, again evidence that the problem was not a

purity problem.



I reread the OP's post several times, and don't see what you mean by non
stationary color shift. From what I read, the purity error was static on
the screen. I'm not a betting man, but I'd bet that if the OP degausses
the TV, the problem will go away.

Yes. I couldn't see where he said that it was a shifting problem, either. I
have seen shifting purity errors, where the shadowmask has become detached
from its frame at one or more of the spot welds. Localised heating from high
luminance areas of the picture can then cause the shadowmask to expand
non-linearly and distort at the point of detachment, resulting in severe,
and non-constant purity errors. On more than one occasion, I have seen a
sort of 'strobing' purity error like a kaleidoscope pattern, as a detached
shadowmask heats and 'pings' and then cools back and then does it again and
so on.

As to purity errors being visible on black and white pictures, other than
the fact that the the phosphors have different efficiencies, and the drive
levels are different for assorted reasons, it doesn't actually matter that
much that the phosphors are being excited by the 'wrong' beams. The mix will
still make something that approximates to white - or shades of grey -
sufficiently well for it not to be glaringly obvious. More a sort of 'dirty
patch' on the picture. However, as soon as a colour picture is viewed on the
same gaussed up CRT, the error is immediately visible

Arfa

 

[Arfa Daily]

I am also saddened to see the era of electronic construction fade away.
No doubt the deterioration of American leadership and expertise in
"building things" is a bigger and related source of disappointment for
those of us who remember this period fondly, and have deep concerns for
our kids and grandchildren.

The Heathkit appeal for me personally wore out as I began to do my own
designs and finished my engineering program. I got heavily into digital,
gave up ham radio (except for radioteletype RTTY), and began buying more
advanced audio and video stuff. My basement in my parent's home looked
like a cross between a wholesale electronics parts supplier and a messy
teenager's bedroom.........

Take a squint at

http://heathkit.com/survey/index.php/278489?lang=en

Arfa

 

[William Sommerwerck]

I would also dispute that a black and white transmission
would not look ok if it was a purity problem.

I've been trying to reason this through. The best I can come up with is
this...

Whether purity is good or bad, the electron beams have to land /somewhere/. In
a B&W image, it might not matter much if red winds up on blue, blue on green,
and green on red. The result will be /something/ approximating a shade of
gray.

 

What most likely happened here is that that the solder connections to the degaussing thermistor went bad and opened up on the initial surge after turnon.

The idea is to magnetise one way and the other at less and less strength, evenually decaying to zero. What hapens in this failure mode is it gets magnetised one way, the connection breaks and the process is incomplete.

Because of the high amperage involved there is usually a brown ring around the connection. To resolder you have to remove the old solder and clean the pin as well as the pad.

The other possibility is the shadow mask (aperature grill in a Sony) cut loose. There is no fix for that, though I can do wonders with magnets around the bell of the CRT. The problem with that is that it might not be stable.

 

It depends a bit on how well the phosphors' efficiency is matched. If the three cathode currents are pretty close, alot of people won't see much. I know what to look for though, and you need the right material to see it, alot of white. If the picture is too busy it is hard to see. Also, if the actual phosphor efficiency is not well matched, they compensated by making the less efficient phosphors larger.

Also a magnetised CRT will exhibit some misconvergence, which is more visible on a high contrast image. You have to look hard though because the color fringes will not be pure red, green or blue.

But yes, in essence those electrons are going to hit somewhere.

 

[Smarty]

On 6/2/2013 9:37 PM, Arfa Daily wrote:

I am also saddened to see the era of electronic construction fade
away. No doubt the deterioration of American leadership and expertise
in "building things" is a bigger and related source of disappointment
for those of us who remember this period fondly, and have deep
concerns for our kids and grandchildren.

The Heathkit appeal for me personally wore out as I began to do my
own designs and finished my engineering program. I got heavily into
digital, gave up ham radio (except for radioteletype RTTY), and began
buying more advanced audio and video stuff. My basement in my
parent's home looked like a cross between a wholesale electronics
parts supplier and a messy teenager's bedroom.........


Take a squint at
http://heathkit.com/survey/index.php/278489?lang=en

Arfa
Excellent !!!!

 

[Smarty]

On 6/2/2013 11:07 PM, William Sommerwerck wrote:

I would also dispute that a black and white transmission
would not look ok if it was a purity problem.

I've been trying to reason this through. The best I can come up with
is this...

Whether purity is good or bad, the electron beams have to land
/somewhere/. In a B&W image, it might not matter much if red winds up
on blue, blue on green, and green on red. The result will be
/something/ approximating a shade of gray.

Yes, but, at least conceptually, the relative proportion of the R,G,B
components at any (and all) landings either are correct, in which case
white (and varying shades of gray) are made, or they are not in the
right proportion, and the resulting color is a pastel.

I would have guessed that a magnetized and thus misaligned set of
landings would not only make green areas appear blue, peripheral areas
to appear red, etc. (such as the form of the original complaint) rather
than maintain uniform white proportions across the CRT. Here is where my
confusion remains, but I simply accept the statements of others here who
actually repair tvs that such is indeed not the case.

 

[Arfa Daily]

"William Sommerwerck" <grizzledgeezer@comcast.net> wrote in message
news:koh10o$kfm$1@dont-email.me...

I would also dispute that a black and white transmission
would not look ok if it was a purity problem.

I've been trying to reason this through. The best I can come up with is
this...

Whether purity is good or bad, the electron beams have to land
/somewhere/. In a B&W image, it might not matter much if red winds up on
blue, blue on green, and green on red. The result will be /something/
approximating a shade of gray.

Correct, as I explain elsewhere in the thread

Arfa

 

[Smarty]

On 6/3/2013 1:07 PM, Arfa Daily wrote:

"William Sommerwerck" <grizzledgeezer@comcast.net> wrote in message
news:koh10o$kfm$1@dont-email.me...
I would also dispute that a black and white transmission
would not look ok if it was a purity problem.

I've been trying to reason this through. The best I can come up with
is this...

Whether purity is good or bad, the electron beams have to land
/somewhere/. In a B&W image, it might not matter much if red winds up
on blue, blue on green, and green on red. The result will be
/something/ approximating a shade of gray.


Correct, as I explain elsewhere in the thread

Arfa

Arfa,

As a newcomer to this group, I hesitate to be a contrarian or appear to
be in any way argumentative or disagreeable. I must admit however that
the notion that random or even partial mis-registration of color is
somehow magically unimportant because the beam has to land someplace
anyway is just totally counter-intuitive and frankly, I believe, wrong.

To make the screen appear white or any non-tinted shade of gray, the
ratio of red, green, and blue is explicitly defined. As soon as some of
the energy intended to light the red phosphor mistakenly lands on the
blue, or any other permutation you may want to consider, the ratio is no
longer producing a shade of gray.

It is certainly obvious when you consider the two extreme limits, one a
single RGB triad, the other the entire faceplate of all triads (stripes)
that if you mis-direct the energy by, let's say, stray magnetism, that
the net effect will be to change the color outcome.Consider these 2
examples:

If, for example, in the single triad case, the red beam was landing on
green rather than red, causing the green phosphor dot to be
disproportionately excited, the color shift would be intuitively to more
green.

At the opposite limit, for the full faceplate, were the red gun's energy
to, somehow, mis-register all of its energy on the green stripes or
neighboring triad dots, the same would be true. The resultant color
would be lacking in red and oversaturated in green.

I use these limit examples as a mental exercise to illustrate my point,
and claim / deduce logically that any example you want to choose in
between will act in the same manner.

If we were talking about power density per square centimeter of energy
being delivered to the faceplate, I would share the conclusion of you
and William, but we are not talking about average power density. The
mis-registration has a consequence when it comes to color purity.

My original and continuing opinion remains that black and white does NOT
mask the purity imperfections as you and William content, but perhaps
this effect is less noticeable because of other considerations (such as
human non-linear ability to perceive chromaticity errors around white
versus our much better ability to discern shades of flesh tones.) This
falls into the murky area of perceptual confusion which allows the brain
and our sensors to easily see some things yet somehow ignore others,
just as is the case for sound and our other senses as well.

I remain fully open to the possibility that black and white does not
reveal purity errors to the same degree for this reason alone, but I do
not in any way buy the argument that mis-aligned / mis-registered
electronics landing on the wrong phosphors is somehow physically
unimportant or invisible due to some odd averaging effect acting to
compensate or some physical phenomena allowing such arbitrary changes in
color proportions to somehow become invisible.

 

[William Sommerwerck]

"Smarty" wrote in message news:koj00i$uvh$1@dont-email.me...

As a newcomer to this group, I hesitate to be a contrarian
or appear to be in any way argumentative or disagreeable.

You didn't hesitate to do it to me. Don't pretend to be "diffident, modest,
and shy", because you aren't.

I don't have as much experience servicing TVs as others in this group. But I
have noticed that impurity is less visible with a monochrome signal than a
color one. Clearly, the visibility will vary with all the factors stated, and
possibly some we've missed.

I can understand your confusion about this point, and it is a point of
confusion I share. But I must remind you of what Sherlock Holmes said, that to
speculate without data weakens the mind.

To argue about what is or is not theoretically visible is a complete waste of
time, when a simple experiment would resolve the issue. (And if anyone reading
this thinks I will slide the yoke on my 13" Trinitron to see what happens --
they are mistaken.)

 

[micky]

On Sun, 2 Jun 2013 20:01:50 -0700 (PDT), jurb6006@gmail.com wrote:

What most likely happened here is that that the solder connections to the degaussing thermistor went bad and opened up on the initial surge after turnon.

The idea is to magnetise one way and the other at less and less strength, evenually decaying to zero. What hapens in this failure mode is it gets magnetised one way, the connection breaks and the process is incomplete.

Because of the high amperage involved there is usually a brown ring around the connection. To resolder you have to remove the old solder and clean the pin as well as the pad.

Sounds good. Because this involves turning the tv around (which
involves cleaning off the kitchen table) I'm saving this one for
third, even though it sounds like something I can do.

Thank you all. I've read all the posts as of last night, and I also
like the idea of degaussing and of using a magnet to see what happens.

Right now, I'm trying to remember where I keep all my magnets. I have
all sizes but the only ones whose whereabouts I know are on the
refrigerator.

The only degaussing coil I have came from a tv I destroyed. I never
found a power supply for it, and right now I also can't remember where
it is. There are only two rooms in the basement. It has to be in
one of them. But anyhow, I went on Freecycle to try to borrow a
degausser. It worked when I needed a metal detector, although it
seems borrowing is against the rules, and some moderators won't
approve a request to borrow. So I say it's a request to be given and
then I'll reccycle it again in a week, including to the original
owner. .

The other possibility is the shadow mask (aperature grill in a Sony) cut loose.

There may well have been a current surge while I was gone (though
nothing else looks bad, so far, and all the clocks were still right
(Yeah, that's not a surge, but still.)

But I don't think there was an earthquake**, so I'm figuring the
aperture grill is still in the right place. When I get to the point
of moving the tv, I'll turn the screen a little and see if that has a
big effect. **We've only had one in 30 years here (Baltimore) and it
was not much. However sitting in the basement at the work bench I
could feel it, so I do get to cross earthquake off my bucket list.

There is no fix for that, though I can do wonders with magnets around
the bell of the CRT. The problem with that is that it might not be
stable.

Without a vow, I'll get back with results when I have them.

 

[Smarty]

On 6/3/2013 5:30 PM, William Sommerwerck wrote:

"Smarty" wrote in message news:koj00i$uvh$1@dont-email.me...

As a newcomer to this group, I hesitate to be a contrarian
or appear to be in any way argumentative or disagreeable.

You didn't hesitate to do it to me. Don't pretend to be "diffident,
modest, and shy", because you aren't.

I have never claimed to be modest or shy, and those who know me would
certainly not categorize me in that manner. As for diffidence, I have a
healthy amount of self confidence in what I say based on an excellent
education and a vast amount of experience.

I do push back when I see a combination of unsupported technical
mumbo-jumbo, particularly when it arises from ignorance, arrogance, or a
combination of the two.

In your case, both attributes are stunningly obvious.

And on the subject of obvious, since you are apparently a fan of
Sherlock Holmes....

The observation of how a black and white image is perturbed by
magnetization can and probably is the cause of your confusion. "There is
nothing more deceptive than an obvious fact" said Holmes in The Bascomb
Valley Mystery". You, William, are easily deceived, and cannot separate
fact from your own technically ignorant notion of how things actually work.

 

[William Sommerwerck]

I do push back when I see a combination of unsupported
technical mumbo-jumbo, particularly when it arises from
ignorance, arrogance, or a combination of the two.

I've been holding off "pushing back" on your generally incorrect views about
surround sound. Coming soon to a UseNet group near you...

 

[John-Del]

On Monday, June 3, 2013 5:35:29 PM UTC-4, micky wrote:

Thank you all. I've read all the posts as of last night, and I also

like the idea of degaussing and of using a magnet to see what happens.

Don't use magnets. There is no reason to try. A strong enough magnet will warp or snap a support in a Trinitron, or at the very least, magnetize one of the mounting brackets which will require repeated degaussing.

As far as your salvaged degauss coil, they use AC. In the TV, it's hit with (generally) 85 VAC* and decays rapidly as the thermistors heat.

*based on 120VAC input.

If you have a variac, wire a plug to the coil and plug it in. Set the variac for 50 to 60 VAC, plug your coil in and wave it around the front of the TV in a circular motion getting within 6" or so, then, continuing the motion, slowly back away from the TV until you get to a few feet away.

 

[micky]

On Sun, 2 Jun 2013 11:19:33 +1000, "Phil Allison" <phil_a@tpg.com.au>
wrote:

"Smarty"

Sounds like a purity problem. Start by degaussing it.

A purity problem would NOT have black and white looking ok as reported in
the original post nor would it result in explicit color replacements as
reported.

** The set is a 19 inch Sony - so it is a Trinitron type.

Yes, Trinitron. I should have said that. Maybe even 25 years old.
I got it used.

I suspect the behaviour is typical of Triniton with a magnetised aperture
grille. The degaussing thermistor may have failed in the set and at the
instant of failure left with a parting blow by magnetising the grille.

The OP can check for this by noting if the usual switch on " bong" noise
still happens.

I have heard the bong sound somewhere, but don't remember heearing it
with this TV. At any rate, I didn't hear the bong when I turned it on
an hour ago, but I wasn't listening for it. I have to go upstairs
again.

He can also bring a magnet near ( not touching) the screen and see if that
tends to fix various areas.

No, it didn't. I used a medium sized magnet. 1" by 5/8" by
3/8"thick and parenthesis-shaped. I think it was one of three magnets
from a picture tube yoke, I guess a color yoke.

It had no effect on black areas and white areas of the screen, but on
other areas, it would drag a yellow ring along with it when I held the
magnet an inch from the screen and moved it around. Yellow is not a
common color on the evening news, so I don't think it fixed anything.

Does all this mean it's not the degaussing circuit?

I put a listing on Freecycle, but to maximize responses, I said I
would "list it again in a week or email the donor". This time I got a
nice email saying my heart was in the right place, but I couldn't
mention anything hinting at giving it back to the guy who gave it to
me.

(This is the third time I've tried to borrow something. One of the
other two times, the moderator permitted it, and the other time he
just refused it, without the compliment and without coaching me on how
to get around it. One time was the metal detector (to try to find
the corner of my property) and I forget what the other thing was.)

Sounds like a color demodulation problem.

** Not likely.


... Phil

 

[Phil Allison]

hrhofmann@sbcglobal.net

There are two things present that have to be understood. There is
convergence, which is making sure the 3 electron beams hit the same
spot/area at the same time. There is purity, which is making sure the
3 beams hit their respective phosphors.

Let us assume that for some reason, all three electron guns come in at
an incorrect angle thru the shadow mask or grid or screen. The blue
electron gun hits 50% on the blue phosphor and 25% on the red and 25%
on the green phosphor. The red gun hits 50% on the red phosphor and
25% on the blue and 25% on the green phosphor. The green gun hits 50%
on the green phosphor and 25% on the red and blue phosphors. All
three phosphors are illuminated at 100%, so only differing electron
beam strengths due to compensating for differing phosphor efficiencies
will be noticeable in any color shading of white and gray areas of the
picture.

Assuing that the convergence of the three images is correct, and only
purity is bad, it will take a trained eye to tell that there is a
purity problem on a B+W picture. But, as soon as a color picture is
presented, colors will be noticeably "off".


** Sounds correct.

When adjusting the " purity magnets " on a conventional CRT, one sets the
test pattern to red and tries to get a even red colour all over the tube
face.

When switched to give a white raster - slight colorations may still appear
in odd spots. These will vary with the orientation of the set too, due to
the earth's mag field, meaning that final adjustment may need to be done in
situ.


.... Phil

 

[hrhofmann@sbcglobal.net]

On Jun 3, 4:30 pm, "William Sommerwerck" <grizzledgee...@comcast.net>
wrote:

"Smarty"  wrote in messagenews:koj00i$uvh$1@dont-email.me...
As a newcomer to this group, I hesitate to be a contrarian
or appear to be in any way argumentative or disagreeable.

You didn't hesitate to do it to me. Don't pretend to be "diffident, modest,
and shy", because you aren't.

I don't have as much experience servicing TVs as others in this group. But I
have noticed that impurity is less visible with a monochrome signal than a
color one. Clearly, the visibility will vary with all the factors stated, and
possibly some we've missed.

I can understand your confusion about this point, and it is a point of
confusion I share. But I must remind you of what Sherlock Holmes said, that to
speculate without data weakens the mind.

To argue about what is or is not theoretically visible is a complete waste of
time, when a simple experiment would resolve the issue. (And if anyone reading
this thinks I will slide the yoke on my 13" Trinitron to see what happens --
they are mistaken.)

There are two things present that have to be understood. There is
convergence, which is making sure the 3 electron beams hit the same
spot/area at the same time. There is purity, which is making sure the
3 beams hit their respective phosphors.

Let us assume that for some reason, all three electron guns come in at
an incorrect angle thru the shadow mask or grid or screen. The blue
electron gun hits 50% on the blue phosphor and 25% on the red and 25%
on the green phosphor. The red gun hits 50% on the red phosphor and
25% on the blue and 25% on the green phosphor. The green gun hits 50%
on the green phosphor and 25% on the red and blue phosphors. All
three phosphors are illuminated at 100%, so only differing electron
beam strengths due to compensating for differing phosphor efficiencies
will be noticeable in any color shading of white and gray areas of the
picture.

Assuing that the convergence of the three images is correct, and only
purity is bad, it will take a trained eye to tell that there is a
purity problem on a B+W picture. But, as soon as a color picture is
presented, colors will be noticeably "off".

I taught color TV servicing at an out-of hours course at Bell
Laboratories 50 years ago and have kept my hand in repairs ever
since. Getting good convergence and purity was/is always a
challenge. Taking tv's on a swivel base and maintaining pruity as the
set is rotated through 120 degrees was always a challenge. The new
flat-screen non-crt tvs are a blessing!!!

 

[Smarty]

On 6/3/2013 9:54 PM, hrhofmann@sbcglobal.net wrote:

There is purity, which is making sure the
3 beams hit their respective phosphors.

Let us assume that for some reason, all three electron guns come in at
an incorrect angle thru the shadow mask or grid or screen. The blue
electron gun hits 50% on the blue phosphor and 25% on the red and 25%
on the green phosphor. The red gun hits 50% on the red phosphor and
25% on the blue and 25% on the green phosphor. The green gun hits 50%
on the green phosphor and 25% on the red and blue phosphors. All
three phosphors are illuminated at 100%, so only differing electron
beam strengths due to compensating for differing phosphor efficiencies
will be noticeable in any color shading of white and gray areas of the
picture.
Your chosen example that the 3 guns are mis-registered uniformly, and

that the phosphors are all illuminated to 100% is not realistic. The
differences in phosphor efficiencies and the necessary beam currents to
achieve comparable light outputs are, as you acknowledged, quite
different. More important is the fact that mis-registered beams are not,
in general, spilling their mis-directed energy to reach 100% phosphor
saturation during a black and white program (versus the full white
example you have chosen). In general they will be generating beam
currents on the average well below peak white and perhaps closer to
black. The instantaneous beam current for, let's say, the least
efficient phosphor's gun, will be mistakenly exciting the most efficient
neighboring phosphors at the same time as the exact opposite is
occurring for nearby areas of the screen owing to the fact that the most
efficient gun is simultaneously exciting the wrong phosphor area with
too little energy. If the proposed mechanism / concept made sense
theoretically, then a black and white picture should not show colored
regions due to magnetization at all.

The ability to discern color differences has as much to do with human
vision as it does with the pure physical radiation of visible light from
the phosphor surfaces, and my partial explanation is that humans see
color variations which are much more subtle at some frequencies compared
to others. White and shades of gray reveal less whereas some color
fields reveal more.

For purposes of our discussion, the esential ingredient of impurity of
color is the non-homogeniety of the electromagnetic field due to
uncontrolled magnetic influences arising from nearby magnetized areas
including the shadow mask. To the extent that we are talking about
pretty drastic purity issues causing large blotches of color, some areas
of the CRT will have gross errors due to landings which are at the
extremes of the convergence system (and thus more likely to be visible)
or beyond the intended raster limits. Recall that the purity control of
the CRT and degausser is intended to deal with the extremely small and
subtle effects of the Earth's magnetic field, whereas abrupt failure of
the degausser is likely to impart a much bigger residual effect unless
corrected. Also, the magnetic distortion is, unlike the Earth's field,
very localized and highly non-linear across the CRT surface, making the
assumption that spoiling of the beams occurs in any uniform way highly
unlikely.

 

[Arfa Daily]

<hrhofmann@sbcglobal.net> wrote in message
news:89f0f7ab-d1bd-44f3-9d6b-76dd2f1bbb0f@b4g2000yql.googlegroups.com...

On Jun 3, 4:30 pm, "William Sommerwerck" <grizzledgee...@comcast.net
wrote:
"Smarty" wrote in messagenews:koj00i$uvh$1@dont-email.me...
As a newcomer to this group, I hesitate to be a contrarian
or appear to be in any way argumentative or disagreeable.

You didn't hesitate to do it to me. Don't pretend to be "diffident,
modest,
and shy", because you aren't.

I don't have as much experience servicing TVs as others in this group.
But I
have noticed that impurity is less visible with a monochrome signal than
a
color one. Clearly, the visibility will vary with all the factors stated,
and
possibly some we've missed.

I can understand your confusion about this point, and it is a point of
confusion I share. But I must remind you of what Sherlock Holmes said,
that to
speculate without data weakens the mind.

To argue about what is or is not theoretically visible is a complete
waste of
time, when a simple experiment would resolve the issue. (And if anyone
reading
this thinks I will slide the yoke on my 13" Trinitron to see what
happens --
they are mistaken.)

There are two things present that have to be understood. There is
convergence, which is making sure the 3 electron beams hit the same
spot/area at the same time. There is purity, which is making sure the
3 beams hit their respective phosphors.

Let us assume that for some reason, all three electron guns come in at
an incorrect angle thru the shadow mask or grid or screen. The blue
electron gun hits 50% on the blue phosphor and 25% on the red and 25%
on the green phosphor. The red gun hits 50% on the red phosphor and
25% on the blue and 25% on the green phosphor. The green gun hits 50%
on the green phosphor and 25% on the red and blue phosphors. All
three phosphors are illuminated at 100%, so only differing electron
beam strengths due to compensating for differing phosphor efficiencies
will be noticeable in any color shading of white and gray areas of the
picture.

Assuing that the convergence of the three images is correct, and only
purity is bad, it will take a trained eye to tell that there is a
purity problem on a B+W picture. But, as soon as a color picture is
presented, colors will be noticeably "off".

That is 100% correct, and an adept description of how such errors are barely
noticeable on a black and white picture. Understand also that we are talking
pure CRT physics here. Don't get confused by colour signal weightings that
are part of the encoding and transmission process. Whilst there are some
differences in the efficiencies of the phosphors, and the eye is non linear
in its response to the visible spectrum, those differences are not huge, and
for white through shades of grey, the three beam currents will not be wildly
different for a CRT that's in good emmissive order. Hence the reason that
mass beam landing errors are not anything like as important to the
reproduction of an accurate grey, as you might imagine. The fact that such
errors are much easier to see on a colour picture may well be a perceptual
one, as the human eye / brain combination, is extremely good at handling
colour perception. Single beam landing errors - convergence errors - are of
course, much easier to see on a black and white picture.

As to questioning the credentials of the people that have replied to this,
being new, you should probably be aware that the William has a lifetime's
experience at the sharp end of service, sales and technical writing, Bob has
lectured the stuff, I spent many thousands of hours of my life working on
this stuff at nuts and bolts level, and Phil, for all his occasional rants
and outbursts, is a highly qualified service engineer whose technical
understanding and ability is without question.

I don't think that any of us have actually said that purity errors are *not*
visible on a black and white picture - they are - but we have all agreed,
based on a collective several lifetimes actually working on this stuff
professionally, that they are nothing like as obvious as they are on a
colour picture, and that someone who is not as well versed in the subject,
may have difficulty seeing such errors under those circumstances, or
identifying exactly what the problem was if they could see them.

Whilst I'm sure that very severe purity errors concentrated in a small
area - such as you used to get when little Johnny helpfully waved a magnet
at the tube face - might show rather more than a 'general' large area purity
error, the fact remains that typical large area errors caused by failure of
the auto degaussing circuit, or turning the set whilst it is on, manifest on
a black and white picture as typically a pastel coloured 'stain' or an area
that looks 'dirty'. I can't really think of a better description than those.

Arfa

I taught color TV servicing at an out-of hours course at Bell
Laboratories 50 years ago and have kept my hand in repairs ever
since. Getting good convergence and purity was/is always a
challenge. Taking tv's on a swivel base and maintaining pruity as the
set is rotated through 120 degrees was always a challenge. The new
flat-screen non-crt tvs are a blessing!!!

 

[Arfa Daily]

"Smarty" <nobody@nobody.com> wrote in message
news:kojq99$gah$1@dont-email.me...

On 6/3/2013 9:54 PM, hrhofmann@sbcglobal.net wrote:
There is purity, which is making sure the
3 beams hit their respective phosphors.

Let us assume that for some reason, all three electron guns come in at
an incorrect angle thru the shadow mask or grid or screen. The blue
electron gun hits 50% on the blue phosphor and 25% on the red and 25%
on the green phosphor. The red gun hits 50% on the red phosphor and
25% on the blue and 25% on the green phosphor. The green gun hits 50%
on the green phosphor and 25% on the red and blue phosphors. All
three phosphors are illuminated at 100%, so only differing electron
beam strengths due to compensating for differing phosphor efficiencies
will be noticeable in any color shading of white and gray areas of the
picture.
Your chosen example that the 3 guns are mis-registered uniformly, and that
the phosphors are all illuminated to 100% is not realistic. The
differences in phosphor efficiencies and the necessary beam currents to
achieve comparable light outputs are, as you acknowledged, quite
different. More important is the fact that mis-registered beams are not,
in general, spilling their mis-directed energy to reach 100% phosphor
saturation during a black and white program (versus the full white example
you have chosen). In general they will be generating beam currents on the
average well below peak white and perhaps closer to black. The
instantaneous beam current for, let's say, the least efficient phosphor's
gun, will be mistakenly exciting the most efficient neighboring phosphors
at the same time as the exact opposite is occurring for nearby areas of
the screen owing to the fact that the most efficient gun is simultaneously
exciting the wrong phosphor area with too little energy. If the proposed
mechanism / concept made sense theoretically, then a black and white
picture should not show colored regions due to magnetization at all.

The ability to discern color differences has as much to do with human
vision as it does with the pure physical radiation of visible light from
the phosphor surfaces, and my partial explanation is that humans see color
variations which are much more subtle at some frequencies compared to
others. White and shades of gray reveal less whereas some color fields
reveal more.

For purposes of our discussion, the esential ingredient of impurity of
color is the non-homogeniety of the electromagnetic field due to
uncontrolled magnetic influences arising from nearby magnetized areas
including the shadow mask. To the extent that we are talking about pretty
drastic purity issues causing large blotches of color, some areas of the
CRT will have gross errors due to landings which are at the extremes of
the convergence system (and thus more likely to be visible) or beyond the
intended raster limits. Recall that the purity control of the CRT and
degausser is intended to deal with the extremely small and subtle effects
of the Earth's magnetic field, whereas abrupt failure of the degausser is
likely to impart a much bigger residual effect unless corrected. Also, the
magnetic distortion is, unlike the Earth's field, very localized and
highly non-linear across the CRT surface, making the assumption that
spoiling of the beams occurs in any uniform way highly unlikely.

All of which is jolly interesting. Pity it doesn't match the actual facts,
as have been repeatedly put to you by a number of people very well qualified
to comment, by virtue of the fact that collectively, they spent a very long
time time working on this stuff at nuts and bolts level, and have probably
seen every possibility of purity error on every type of CRT and under every
set of circumstances possible ...

Arfa