What happens as CRTs die?

[Ian Stirling]

I have a modestly old (1988 or so) TV.
On low brightness it's more or less OK.
When the brightness is turned up, convergance goes out of the window.
(blue out of the left window, red out of the right)

Is this a normal symptom of age, in which case it's probably going for a
little trip..., or likely to be some other failure, that could possibly
be remedied?

--
http://inquisitor.i.am/ | mailto:inquisitor@i.am | Ian Stirling.
---------------------------+-------------------------+--------------------------
"Melchett : Unhappily Blackadder, the Lord High Executioner is dead
Blackadder : Oh woe! Murdered of course.
Melchett : No, oddly enough no. They usually are but this one just got
careless one night and signed his name on the wrong dotted line.
They came for him while he slept." - Blackadder II

 

[Charles Schuler]

"Ian Stirling" <root@mauve.demon.co.uk> wrote in message
news:bh3rio$6sp$3$8302bc10@news.demon.co.uk...

I have a modestly old (1988 or so) TV.
On low brightness it's more or less OK.
When the brightness is turned up, convergance goes out of the window.
(blue out of the left window, red out of the right)

Is this a normal symptom of age, in which case it's probably going for a
little trip..., or likely to be some other failure, that could possibly
be remedied?

If it was an automobile, it would have 300,000 miles on it. Seriously, the
CRT no doubt suffers from low emission, the electrolytic capacitors are
leaky and have lost much of their capacitance, the semiconductor junctions
are leaky, the resistors have drifted out of tolerance, etc. Be kind and
shoot it in the head when it's not looking.

 

[Paul Landregan]

could be that the drive cct for the deflector coils is weak. As the
brightness increases so does the velocity of the electrons, needing a bigger
force to move them in the correct place. If the magnets cannot provide this
force at the correct time the electrons will not be moved correctly.

Just a thought from the physics point of view.

"Ian Stirling" <root@mauve.demon.co.uk> wrote in message
news:bh5346$cn5$3$830fa78d@news.demon.co.uk...

Charles Schuler <charlesschuler@comcast.net> wrote:

"Ian Stirling" <root@mauve.demon.co.uk> wrote in message
news:bh3rio$6sp$3$8302bc10@news.demon.co.uk...
I have a modestly old (1988 or so) TV.
On low brightness it's more or less OK.
When the brightness is turned up, convergance goes out of the window.
(blue out of the left window, red out of the right)

Is this a normal symptom of age, in which case it's probably going for
a
little trip..., or likely to be some other failure, that could possibly
be remedied?

If it was an automobile, it would have 300,000 miles on it. Seriously,
the
CRT no doubt suffers from low emission, the electrolytic capacitors are

Oh, I'm sure it's old, and the CRT will be less bright than it once was.
However, it's adequately bright, at maximum brightness, and I'm wondering
exactly what the symptoms of low emission should be.

If the poor convergance at high brightness indicates that the tube is in
fact
dying, then there is little point even spending an hour or three in
attempting a repair.

--
http://inquisitor.i.am/ | mailto:inquisitor@i.am | Ian
Stirling.
---------------------------+-------------------------+--------------------
------
Things a surgeon should never say:
Better save that for the autopsy.

 

[William R. Walsh]

Hi!

If it was an automobile, it would have 300,000 miles on it.

Generalizations really don't hold for consumer electronics. Some die
in or just out of warranty; some go on for way past their design lifetime.

I agree with Sam on this. You can't really say the automobile thing either.
I've seen cars with 200 or 300 thousand miles on the odometers that almost
look brand new and run very nicely. I would tell you that is the time when
they just get broken in!

Then I've seen cars with 60 thousand miles about to fall apart...rusty
bodies, broken interiors and beat up driveline parts...

It seems to be in how the owners take care of their vehicles.

Of course, what is also relevant is how much it was used!

Almost all of it depends on how the device was used.

William

 

[t.hoehler]

I've got a good understanding of what the TV should do, deflection, ...
I don't really know if a low emission tube can cause convergance problems.
I don't see any obvious mechanisms, hence the original question.

I bet your assumptions are correct. I don't think the problem is in the crt.
I have a very old dim tube sony set my son uses for video games, the room
must be very dark to view, but the convergence is still quite accurate.
Something else is going on there.
Regards,
Tom

 

[Ian Stirling]

H. R. Bob Hofmann <hrhofmann@att.net> wrote:
<snip my question>

A very simple fix for older CRTs that have low emission is to raise
the filament voltage slightly. This used to be done, when filaments
were powered from a 60Hz trsansformer, with a step-up filament
transformer.

I've got a good understanding of what the TV should do, deflection, ...
I don't really know if a low emission tube can cause convergance problems.
I don't see any obvious mechanisms, hence the original question.

--
http://inquisitor.i.am/ | mailto:inquisitor@i.am | Ian Stirling.
---------------------------+-------------------------+--------------------------
The fight between good and evil, an epic battle. Darth vader and Luke,
suddenly in the middle of the fight, Darth pulls Luke to him, and whispers
"I know what you'r getting for christmas!" Luke exclaims "But how ??!?"
"It's true Luke, I know what you'r getting for christmas" Luke tries to ignore
this, but wrenches himself free, yelling "How could you know this?",
Vader replies "I felt your presents" -- The Chris Evans breakfast show ca. 94

 

[David]

I have seen the corners go so out of focus that the convergence is also out
of whack.

This might be what he is trying to describe. If it is a Sony or NEC crt
with the h-stat in the tube, those do have convergence errors as the tube
gets weak.

David

James Sweet <jamessweet@hotmail.com> wrote in message
news:fWvZa.114310$Ho3.14832@sccrnsc03...

Dying CRT's are typically dim and fuzzy, I've never seen one go out of
convergence, that sounds like something else.

"Ian Stirling" <root@mauve.demon.co.uk> wrote in message
news:bh5346$cn5$3$830fa78d@news.demon.co.uk...
Charles Schuler <charlesschuler@comcast.net> wrote:

"Ian Stirling" <root@mauve.demon.co.uk> wrote in message
news:bh3rio$6sp$3$8302bc10@news.demon.co.uk...
I have a modestly old (1988 or so) TV.
On low brightness it's more or less OK.
When the brightness is turned up, convergance goes out of the window.
(blue out of the left window, red out of the right)

Is this a normal symptom of age, in which case it's probably going
for
a
little trip..., or likely to be some other failure, that could
possibly
be remedied?

If it was an automobile, it would have 300,000 miles on it.
Seriously,
the
CRT no doubt suffers from low emission, the electrolytic capacitors
are

Oh, I'm sure it's old, and the CRT will be less bright than it once was.
However, it's adequately bright, at maximum brightness, and I'm
wondering
exactly what the symptoms of low emission should be.

If the poor convergance at high brightness indicates that the tube is in
fact
dying, then there is little point even spending an hour or three in
attempting a repair.

--
http://inquisitor.i.am/ | mailto:inquisitor@i.am | Ian
Stirling.

---------------------------+-------------------------+--------------------
------
Things a surgeon should never say:
Better save that for the autopsy.

 

[H. R. Bob Hofmann]

Ian Stirling <root@mauve.demon.co.uk> wrote in message news:<bh5vc6$375$3$8302bc10@news.demon.co.uk>...

H. R. Bob Hofmann <hrhofmann@att.net> wrote:
snip my question
A very simple fix for older CRTs that have low emission is to raise
the filament voltage slightly. This used to be done, when filaments
were powered from a 60Hz trsansformer, with a step-up filament
transformer.

I've got a good understanding of what the TV should do, deflection, ...
I don't really know if a low emission tube can cause convergance problems.
I don't see any obvious mechanisms, hence the original question.

--
http://inquisitor.i.am/ | mailto:inquisitor@i.am | Ian Stirling.
---------------------------+-------------------------+--------------------------
The fight between good and evil, an epic battle. Darth vader and Luke,
suddenly in the middle of the fight, Darth pulls Luke to him, and whispers
"I know what you'r getting for christmas!" Luke exclaims "But how ??!?"
"It's true Luke, I know what you'r getting for christmas" Luke tries to ignore
this, but wrenches himself free, yelling "How could you know this?",
Vader replies "I felt your presents" -- The Chris Evans breakfast show ca. 94

When the cathode material coating wears out, the bias on the guns has
to be "turned up" to get the same amount of emissions from the
cathode. This operation of the electron gun out of its "normal"
design range frequently causes defocussing of the electron beam itself
and leads to the apparent mis-convergence. All I can do is suggest
that you raise the gun voltage and see what happens. You could also
just power the filaments from a variable power supply and see what
happens. I can't guarantee that it will work, but I have probably
done this to several dozen tv sets with virtually 100% success.

H. R. (Bob) Hofmann

 

[Ian Stirling]

H. R. Bob Hofmann <hrhofmann@att.net> wrote:

Ian Stirling <root@mauve.demon.co.uk> wrote in message news:<bh7lnm$47f$1$8300dec7@news.demon.co.uk>...
David <dkuhajda@locl.net.spam> wrote:
I have seen the corners go so out of focus that the convergence is also out
of whack.

This might be what he is trying to describe. If it is a Sony or NEC crt
with the h-stat in the tube, those do have convergence errors as the tube
gets weak.
snip description
That's pretty much what I described in my Aug 10 post.

Yes, it is.
I suspect I'll try upping the voltage on the heater a tad.
Thanks for the help.

--
http://inquisitor.i.am/ | mailto:inquisitor@i.am | Ian Stirling.
---------------------------+-------------------------+--------------------------
If God hadn't intended us to eat animals,
He wouldn't have made them out of MEAT! - John Cleese