What makes this happen on a projection tv?

[Nick]

I've got a projection tv here with the blue gun having trouble.

It seems that theres some kind of curl.. or dip in the top. the bottom lines
up perfectly fine. Is this some kind of yoke problem? I can't imagine what
else would affect a tube like that..

The problem follows the tube when i switch the color inputs or the yoke
connectors..

Here's a picture to explain it better.
http://home.comcast.net/~slicknick1981/html/monitor.jpg

Thanks for any help,
Nick

 

[Mark D. Zacharias]

I've got a projection tv here with the blue gun having trouble.

It seems that theres some kind of curl.. or dip in the top. the bottom
lines up perfectly fine. Is this some kind of yoke problem? I can't
imagine what else would affect a tube like that..

The problem follows the tube when i switch the color inputs or the yoke
connectors..

Here's a picture to explain it better.
http://home.comcast.net/~slicknick1981/html/monitor.jpg

Thanks for any help,
Nick

Convergence amp problems. Are you qualified from a technical standpoint?
A knowledgeable type could probably repair this himself, but an average
do-it-yourself-er would probably just ugly up the board so badly I wouldn't
want to even suggest they try it.


Mark Z.

 

[Art M - Artfromny]

there are 2 or 3 large ICs on a heat sink in there - maybe 2 1/2" x 1 1/2
inches - they will be in the STK series
the blue convergence amp is bad and there may be a few very low value 1 or 2
watt resistors that failed as well - they will often look burnt or
discolored

As Mark Z so accurately pointed out if you cant solder well and are not
familiar with component level repair, this is not a job for you to do
yourself - the pads under those 18 and 20 pin ICs are generally small and
thin and its easy to damage them and their traces taking out the old IC

depending on your area you can expect to pay between 200 and 400 dollars to
get that done in home, assuming you use a professional outfit rather than
the garage tech - I am in the Albany NY area and I get 365 for the job

one suggestion - if that is a Phillips Sony or Hitachi TV make VERY VERY
sure that you do not use generic parts - insist on the manufacturer's
version of the part and expect to pay 25 to 35 for it, including shipping -
this is especially critical if you expect the job to last more than a few
weeks - and it will also make the re-alignment afterwards much easier

 

[TMI]

Since this follows the tube/yoke, I do not agree with the others on
this (unless the chip they describe is part of the yoke assembly).

At first, I assumed you had a mechanical allignment issue where the
blue tube is set too low and you are alligning above the linear region
of the raster. The cure for this is to adjust the tube to point higher
on the screen and re converge.

The correct proceedure is to center the raster on each tube, looking
into the lens, then adjust each tube mechanically for best on screen
overlay coverage, then proceed to electrical convergence.

The nature of the whip in your photo is curious and could be caused by
a shifted linearity magnet, some stray magnetic field or a cap within
the yoke failing. Check the rings on the neck end of the yoke, note
their position and swing them around a bit to see if it addresses the
problem. Look for missing or shifted bias magnets. As a last resort,
open the yoke housing and start replacing the caps inside, clean any
spark gaps etc.

Tom Maguire

 

[TMI]

Since this follows the tube/yoke, I do not agree with the others on
this (unless the chip they describe is part of the yoke assembly).

At first, I assumed you had a mechanical alignment issue where the
blue tube is set too low and you are aligning above the linear region
of the raster. The cure for this is to adjust the tube to point higher
on the screen and re converge.


The correct procedure is to center the raster on each tube, looking
into the lens, then adjust each tube mechanically for best on screen
overlay coverage, then proceed to electrical convergence.


The nature of the whip in your photo is curious and could be caused by
a shifted linearity magnet, some stray magnetic field or a cap within
the yoke failing. Check the rings on the neck end of the yoke, note
their position and swing them around a bit to see if it addresses the
problem. Look for missing or shifted bias magnets. As a last resort,
open the yoke housing and start replacing the caps inside, clean any
spark gaps etc.


TMI

 

[Leonard Caillouet]

Convergence amp problems. Are you qualified from a technical standpoint?
A knowledgeable type could probably repair this himself, but an average
do-it-yourself-er would probably just ugly up the board so badly I
wouldn't want to even suggest they try it.


Mark Z.

There is some good info for DIYers for convergence output repairs at

http://www.hometheatershack.com/for.../5600-crt-based-rptv-convergence-repairs.html

Leonard

 

[Art M - Artfromny]

I am almost 100% sure this is an amp problem; I fix 6 to 8 of these a week
and have only on one occasion had to change a convergence yoke, and it was
giving a decent picture but destroying the associated STK in a few days.

Also you need to bear in mind that there are 2 yokes per tube on many PTVs
one deflection and one convergence.

Also absent any moving or dropping of the TV there is no reason for the
magnets, rings, yokes, etc to have shifted from their proper positions.

I do this for a living, that doesnt mean I am always right (I am not) but I
would be surprised to be wrong on this one.

 

[TMI]

Dear Art,

I bought out most of the surplus from Advent and installed the first
1000A in a bar in NYC so I've been at this a while too.

If it is the STK module, how could it "follow the tube/yoke" when he
swaps the connections with say the red? Splain please?.

I have no experience with this unit in particular but, if it follows
the yoke when swapped with another color's (that would mean the yoke
is now connected to an STK module that IS working correctly), that
means it is a tube/yoke issue-not a deflection amp issue.

If there is a static magnet (like Sony is fond of) that has become
unglued due to heat, sometimes this can result.(Compare to the other
tubes and look for missing magnets)

Granted, linearity rings do not move by themselves and it's an odd
drop that moves them this much and only on one color. We don't know
the history and there could have been busy fingers at work before he
got it.

What is more likely is damage to the internal gun support. If it is
stable, a new setting of the linearity rings may help.

TMI

 

[Art M - Artfromny]

Very good point indeed

the only other thing that would support the STK diagnosis is that when you
swap STK outputs the result is not always a correct convergence, merely a
different one - due to the alignment info coming out of the DCU the red will
not properly align the blue that it is now driving when switched, but it
will change the pattern of mis-convenrgence, and to an untrained eye it may
look like the problem is following the yoke

it is quite frustrating to diagnose a problem long distance like this - I
will be very interested to see the final answer

 

[Leonard Caillouet]

Dear Art,

If it is the STK module, how could it "follow the tube/yoke" when he
swaps the connections with say the red? Splain please?.

Depends on whether the deflection yoke or the convergence yoke wires were
swapped. If the deflection yoke wires were swapped it would have the same
convergence drive.

Leonard

 

[Art]

Swapping the convergence connections would switch distortion from one tube
to another, swapping the deflection connections would have minimual effect.

 

[Mr. Land]

Dear Art,

I bought out most of the surplus from Advent and installed the first
1000A in a bar in NYC so I've been at this a while too.

Wow, are you talking about the old Advent projectors, white, stand in
the middle of the floor, looks a little like R2D2, has dozens of plug-
in boards inside, runs the tubes at around 50KV? I used to work on
those!!!

 

[clifto]

Wow, are you talking about the old Advent projectors, white, stand in
the middle of the floor, looks a little like R2D2, has dozens of plug-
in boards inside, runs the tubes at around 50KV? I used to work on
those!!!

I serviced a few myself. I remember best the one on the fifty-something
floor of Lake Point Towers in Chicago. I had to "phone home", and the
customer's phone was on a three-foot cord plugged into a jack right by
an extremely large plate-glass window. My acrophobia insisted that I
crawl on hands and knees to the phone and keep my call short.