HELP...Sony KP-48V-75 Defocus adjustment

[jim's]

Wondering how to make this adjustment. The service manual states to
adjust the FOCUS knob? I can not find it, can someone point me in the
right direction on this one?
The reason, I think, this need to be adjusted is that the "blue lines"
have a halo of blue around them.
Thanks for the help.
Jim

 

[Jerry G.]

In do not know for your specific model, but the focus pot is usually on
the high voltage multiplier or on the CRT circuit board, or a control
board for it. In most sets the multiplier is part of the flyback assy.
Near to the focus controls are usually the G2 or screen bias control(s).
Take care to not adjust the bias for no reason.

Note: If the set was good before, and is now having soft focus problems,
this means that something is failing. This looks like it may be a tube
problem. Following the schematic, and looking at the references for
it, the bias voltages at the CRT sockets, and the supply sources should
be verified

--

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Wondering how to make this adjustment. The service manual states to
adjust the FOCUS knob? I can not find it, can someone point me in the
right direction on this one?
The reason, I think, this need to be adjusted is that the "blue lines"
have a halo of blue around them.
Thanks for the help.
Jim

 

[David]

How much 'blue halo"?
Sony low end RPTV sets, especially those with the narrow cabinet have an
average optical focus on the red and blue due to not using the more
expensive lenses that compensate for the difference in distance between the
left and right tubes.
In addition due to the lower output of the phosphor, the blue is out of
focus by design to allow proper gray scale tracking. A certain amount of
defocus is expected and normal. This is why the amount of halo is very
important and critical to determine if there really is an adjustment needed.

It could simply be the blue tube is getting soft with age and is outside of
proper focus range.

Most Sony RPTV sets use a focus block on the hv divider for electrical
focus, there is also an optical focus. It is strongly suggested you consult
the service adjustment manual to verify the proper focus procedure and
amount for the blue tube. You will likely find that a gray scale adjustment
will be required after adjusting the blue focus on that set.

David

 

[Leonard Caillouet]

A KP48V75 should not be a point in its service life where the CRTs are no
focusing well unless it has been run much more than a typical consumer
would. It probably came from the factory looking like this. I don't recall
if Sony intentionally defocused the blue on this one or not and the Sony ESI
site is not coming up at all and my discs are at the shop. Has anyone else
been having trouble getting to the site for the last few days?

Blue phosphors do not focus as tightly as red and green, true enough. It is
not, however, necessary to defocus the blue to get good white balance or
gray scale tracking. The reason that many manufacturers defocused the blue
was to get more output, this is correct. This accomplished two things, a
brighter picture at white peak (desirable in showroom comparisons) at a
higher color temperature (more blue whites a.k.a. a "trinitron" look with
pinker flesh tones). Running the contrast a little lower, focusing the blue
correctly (for best focus), and readjusting the white balance for your
preferred color temperature almost always gives a better result and also
gives longer tube life with less burn-in problems. RPTV brightness levels
have bee higher than needed for good viewing in a normal home environment
for years. "Torching" the CRTs the way the manufacturers set them up is
simply not necessary.

Even if the service manual says to defocus the blue that does not mean that
it is the best solution. The approximately 9500 degree color temperature
that the manufacturers are (were) able to get by doing so is considered by
most people who understand color reproduction, and many casual viewers, to
be "wrong". Actually the practice of defocusing the blue has been going
away as we move to HD because there is agreement that a lower color
temperature is more correct and the defocusing procedure limits resolution.
Nobody wants a "soft" HD image and most HD buyers are more attentive to
issues such as color temperature, focus, and convergence.

A good reference document with more than most of us want to know about color
is provided by Charles Poynton at
http://www.poynton.com/PDFs/ColorFAQ.pdf

Leonard Caillouet

 

[jim's]

Hello Guys,
Thanks for the reply and the information!!.

The "blue halo", I feel, is pretty bad. While looking at white letters, a blue
shadow can be seen on the lower and right side. While doing the convergence
set-up, I have the same issue. I was able to turn off the green and red guns,
what I see is that the blue cross is very blurry, much more so then the other
two. I did adjust the blue on the focus block, I can not get it any clearer. I
also try adjusting the len focus, no luck there either.
I was hoping there is one more adjustment called the defocus as stated in the
service manual. They state it is for the blue only and you would use the focus
knob to get a 12- 13mm bar across the screen.

Thanks again for the help, and if you have any other ideas I would love to here
them

 

[David]

If when you look directly in the blue tube the electrical focus will not
make the line clear on the phosphor, it is highly likely the tube is simply
getting weak.

I have seen way too many 3 to 4 year old, even Sony, RPTV sets with soft
blue crt's. Especially when used in an average household, factory preset
picture settings from day one, left on minimum of 6 hours a day during the
week and 20 hours a day on the weekend.

The sure fire way to be sure is to swap the crt board between the red and
blue tube. (this may require moving the tubes themselves, 4 or 8 screws to
do it). If the focus problem stays with the blue tube, it is the tube
itself.

The defocus as mentioned in the manual is to deliberately make the blue out
of focus for the factory specifications.