Advice on adjusting yoke on TV pic tube

[Alan]

With letterbox video, you can see that the picture on my couple years
old Sony 32" is rotated slightly from the horizontal (the picture
itself is a correct rectangle). There is no adustment that will fix
this in the service menu. I got a TV repair book out of the library,
and it looks like all I have to do to correct it is to loosen the
deflection yoke clamp and rotate the yoke slightly. Shouldn't be a
problem, I'm an accomplished home appliance fix it yourselfer. But I
read that the picture tube can hold a high voltage charge for several
days (as well as that there's all sorts of high voltage stuff in TVs
anyway).

My question is, is it dangerous to touch to tube itself as opposed to
the electrical terminals on it? I'm not intending to touch any
electrical contact points, or do anything with the electronics, just
loosen the yoke and turn it a little, but I thought I should check
with Those Who Know in the forum.

Thanks

 

[john]

You want the Truth..
Leave it alone you will effect
the overall convergence.

kip

 

[David]

Don't Do It.
Any movement of the yoke will effect geometry, convergence, and purity.
Unless you are equipped and have all the training and equipment required to
perform all those adjustments after screwing with the yoke, do not touch it.

Depending on how far it is rotated, the Earth's magnetic field will cause
rotation. On a 27" size tube it can be as much as 1" variance from left to
right depending on where you live, in the US, and the direction the tv set
is facing.

This is why many of the 'better' higher end and larger tv sets include in
the USER menu or a set of switches on the back a tilt correction circuit.

David

 

[James Sweet]

With letterbox video, you can see that the picture on my couple years
old Sony 32" is rotated slightly from the horizontal (the picture
itself is a correct rectangle). There is no adustment that will fix
this in the service menu. I got a TV repair book out of the library,
and it looks like all I have to do to correct it is to loosen the
deflection yoke clamp and rotate the yoke slightly. Shouldn't be a
problem, I'm an accomplished home appliance fix it yourselfer. But I
read that the picture tube can hold a high voltage charge for several
days (as well as that there's all sorts of high voltage stuff in TVs
anyway).

My question is, is it dangerous to touch to tube itself as opposed to
the electrical terminals on it? I'm not intending to touch any
electrical contact points, or do anything with the electronics, just
loosen the yoke and turn it a little, but I thought I should check
with Those Who Know in the forum.

Thanks

I wouldn't worry too much about getting shocked, just don't touch exposed
connections. What I would worry about is messing up the convergence and
other settings, I adjust yokes frequently on old arcade game monitors, you
just fire up the monitor, put a test pattern on the screen, loosen the clamp
and rotate the yoke until it's straight then clamp it down, but these are
generally basic 19" shadow mask tubes, I'd be hesitant to mess with a big
Trinitron unless it's really bad.

 

[Patch]

With letterbox video, you can see that the picture on my couple years
old Sony 32" is rotated slightly from the horizontal (the picture
itself is a correct rectangle). There is no adustment that will fix
this in the service menu. I got a TV repair book out of the library,
and it looks like all I have to do to correct it is to loosen the
deflection yoke clamp and rotate the yoke slightly. Shouldn't be a
problem, I'm an accomplished home appliance fix it yourselfer. But I
read that the picture tube can hold a high voltage charge for several
days (as well as that there's all sorts of high voltage stuff in TVs
anyway).

My question is, is it dangerous to touch to tube itself as opposed to
the electrical terminals on it? I'm not intending to touch any
electrical contact points, or do anything with the electronics, just
loosen the yoke and turn it a little, but I thought I should check
with Those Who Know in the forum.

Thanks

Don't mess with the yoke, put a couple of shims under the low side. LOL

 

[techforce]

Actually, thats probably the cause of the problem. The Earths Magnetic Field
probably shifted somewhat enough to only be reflective in this particular
set.

According to Discovery channel, the Polarity of the Earths Magnetic Field
has Reversed at least once in I think it was 4 million years?



| Depending on how far it is rotated, the Earth's magnetic field will cause
| rotation. On a 27" size tube it can be as much as 1" variance from left
to
| right depending on where you live, in the US, and the direction the tv set
| is facing.

 

[H. R. Bob Hofmann]

Don't mess with the yoke, put a couple of shims under the low side. LOL

First I would paint a nail polish or some other fast-drying paint
stripe between the yoke and something that is fixed, like the pic tube
itself, to allow me to get back to zero. I would then rotate the yoke
slightly, maybe half of what correction I thought would be needed.

I would stop at that point, and see what the results look like on the
picture side of the set, is it straighter, is the convergence,
especially around the edges no worse than what it was before, are the
reds still red (for a purity check), etc. If the results were ok at
that point, I would do another rotation and see if all is still ok.

If the midpoint has introduced more problems, the painted stripe will
allow you to get back to ground zero, then put the shims under one
side of the set as suggested and don't put anything on top that is wet
and might spill into the set

H. R. (Bob) Hofmann

 

[Asimov]

"john" bravely wrote to "All" (26 Feb 04 18:06:21)
--- on the heady topic of "Re: Advice on adjusting yoke on TV pic tube"

jo> Reply-To: "john" <[email protected]>
jo> From: "john" <[email protected]>

jo> You want the Truth..
jo> Leave it alone you will effect
jo> the overall convergence.

The point of "convergence" is to correct for magnetic field anomalies
mainly arising in the deflection coil windings. The crt is by far a
more precise device. Rotating the yoke a couple of degrees therefore
should not affect convergence noticably because the magnetic offset
tabs still align correctly with the deflection coil defects. Obviously
any effects of the rotation should be observable at the edges of the
crt first, so a white line crosshatch would be a good pattern to
monitor the changes as the yoke is rotated. Try it on a junker and
see.

Asimov
******

.... High voltage can give a dangerously uncomfortable discharge.