Purity problem in Panasonic TV

[Jeroni Paul]

Hello
I've got a Panasonic TV model TX-29AS10F chasis EURO-4H with a color
purity problem at both sides of top of the picture. Top left has a
greenish tint and top right is yellowish, the rest is correct
including top middle. That discoloration gets worse as nearer to the
edge. This model is 100Hz and has a completely flat CRT front.

In the user settings it has a geomagnetic correction menu that lets
the user rotate the picture slightly, the curious thing is that
adjusting that also moves that purity defect. The right one can be
eliminated completely this way but then the left one expands even
more. The opposite is also true but the left one can't be corrected
completely.

I wonder if you belive it is more probably a CRT mask defect, a moved
or misaligned yoke or some missing/fallen magnets. I don't see
anything wrong apparently in the yoke but before I start playing with
small magnets around the tube or moving the yoke I ask for previous
experiences.

Thank you.

 

[hr(bob) [email protected]]

Hello
I've got a Panasonic TV model TX-29AS10F chasis EURO-4H with a color
purity problem at both sides of top of the picture. Top left has a
greenish tint and top right is yellowish, the rest is correct
including top middle. That discoloration gets worse as nearer to the
edge. This model is 100Hz and has a completely flat CRT front.

In the user settings it has a geomagnetic correction menu that lets
the user rotate the picture slightly, the curious thing is that
adjusting that also moves that purity defect. The right one can be
eliminated completely this way but then the left one expands even
more. The opposite is also true but the left one can't be corrected
completely.

I wonder if you belive it is more probably a CRT mask defect, a moved
or misaligned yoke or some missing/fallen magnets. I don't see
anything wrong apparently in the yoke but before I start playing with
small magnets around the tube or moving the yoke I ask for previous
experiences.

Thank you.

Is the degaussing circuit working. IF you are not sure, get hold of a
degausssing coil and manually degauss the CRT. You don't say if this
is a new problem or was that waay from the beginning, and what might
have happened such as dropping the set, or unplugging a vacuum cleaner
right next to the set, or whatever. These are im[portant clues.

H. R. (Bob) Hofmann

 

[Jeroni Paul]

hr(bob) [email protected]:

Is the degaussing circuit working. IF you are not sure, get hold of a
degausssing coil and manually degauss the CRT.

Thank you for replying.
It appears to be working according to the noise it makes at startup.

You don't say if this
is a new problem or was that waay from the beginning, and what might
have happened such as dropping the set, or unplugging a vacuum cleaner
right next to the set, or whatever. These are im[portant clues.

I know, but unfortunately I don't have this info since it came from
the scrap. A good starting point is that there was some evidence that
it was neven been opened.

 

[Jeroni Paul]

hr(bob) [email protected]:

Is the degaussing circuit working. IF you are not sure, get hold of a
degausssing coil and manually degauss the CRT.

Thank you for replying.
It appears to be working according to the noise it makes at startup.

You don't say if this
is a new problem or was that waay from the beginning, and what might
have happened such as dropping the set, or unplugging a vacuum cleaner
right next to the set, or whatever. These are im[portant clues.

I know, but unfortunately I don't have this info since it came from
the scrap. A good starting point is that there was some evidence that
it's neven been opened.

 

[Jeroni Paul]

hr(bob) [email protected]:

Is the degaussing circuit working. IF you are not sure, get hold of a
degausssing coil and manually degauss the CRT. You don't say if this
is a new problem or was that waay from the beginning, and what might
have happened such as dropping the set, or unplugging a vacuum cleaner
right next to the set, or whatever. These are im[portant clues.

I have checked the degaussing coils operate correctly as playing with
magnets I've magnetized the CRT and a cold degauss restored it. They
also make a very audible noise.

Have been playing with some magnets around the tube and found that
placing a small magnet at the right orientation around the deflection
coils next to the tube gets rid of the purity problem. Two magnets,
one per discoloration, I can get it perfect.

However I wonder if that is the solution to the problem or should I
look elsewhere for something misaligned. The yoke appears firmly
attached to the tube without signs of having moved, it is glued there.
The convergence / purity rings are intact with their original painting
as well as some adjustment screws around the coils.

I have noticed there are three windings electronically controlled,
probably used for rotation. One next to the convergence / purity
rings, one around the deflection coils next to the tube and one around
the entire tube together with degaussing coils. What do these do?
Could a failure of one of these cause the problem (I mean the
electronics that control them)?