Hello: I have a Sony PTV Model # KP-46XBR25 DOP 9/93 in my shop which
has an intermittent video problem. When the set is started up from a
cold start, the raster is black for about two minutes. Then, the video
appears and disappears to black at the rate of about once per second.
If I adjust the screen voltage pots slightly up or down (Especially the
blue) the blinking on and off will slow or stop completely - but the
adjustments to do this throws the gray scale off to an unacceptable
tint.Also, the blink rate seems to vary with scene brightness. I have
seen similar symptons in late 90s Sony 27-32" Table model sets which
had a problem with the screen voltage setting on the flyback being
critical or the CRT emission too far off on one color. I read
something on the Internet about another XBR Sony having a problem with
Capacitor C1737 on the "D" board. The audio and delction and tuning on
this set are always fine. I would appreciate some tips, list of parts
to check, or scans of some service data on this model. Thank you!

Robert McPherson
McPherson Electronics
Telephone (502) 367-9324
Cellphone (502) 298-6997

Email

wrote:
Hello: I have a Sony PTV Model # KP-46XBR25 DOP 9/93 in my shop which
has an intermittent video problem. When the set is started up from a
cold start, the raster is black for about two minutes. Then, the video
appears and disappears to black at the rate of about once per second.
If I adjust the screen voltage pots slightly up or down (Especially the
blue) the blinking on and off will slow or stop completely - but the
adjustments to do this throws the gray scale off to an unacceptable
tint.Also, the blink rate seems to vary with scene brightness. I have
seen similar symptons in late 90s Sony 27-32" Table model sets which
had a problem with the screen voltage setting on the flyback being
critical or the CRT emission too far off on one color. I read
something on the Internet about another XBR Sony having a problem with
Capacitor C1737 on the "D" board. The audio and delction and tuning on
this set are always fine. I would appreciate some tips, list of parts
to check, or scans of some service data on this model. Thank you!

Robert McPherson
McPherson Electronics
Telephone (502) 367-9324
Cellphone (502) 298-6997

Email

Simple to fix, replace all three picture tubes. The cause is the AKB
circuit is blanking the video because one or more of the picture tubes
is too far out of balance compared to the other tubes or all three are
below specification and the AKB cannot compensate. Given the symptom
of the gray scale being way off when the blinking stops pretty much
guarantees that the problem is the picture tubes.

David

rm502 is quite right about the pix tubes being the cause, but you
MAY be able to "tweak" the EEPROM parameters in the service
menu to get a good grey scale, after the G2 screen adjustments are
set to stop the "famous Sony CRT flash"! Have you guys ever done
a CRT boost on these projection CRT's? If so, have they lasted, &
how do they look after pix wise? Sony CRT's in direct-view units
look pale, & not so good after a boost, although most customers
don't complain, I wouldn't like to watch it after a boost.

I have a Sencore CR-70 rejuvinator, but it only has a socket # 3, # 4.
I haven't tried to boost them yet. I ask you guys, is a there a way to
"work around" the AKB problem? Iv'e seen info about adding resistors
to "tweak" the pix to stay on, even though it isn't as nice a pix, but quite
watchable. Sky.

NEDSA of Ohio has a good article on this under the featured articles
"Skype_man" wrote in message
...
rm502 is quite right about the pix tubes being the cause, but you
MAY be able to "tweak" the EEPROM parameters in the service
menu to get a good grey scale, after the G2 screen adjustments are
set to stop the "famous Sony CRT flash"! Have you guys ever done
a CRT boost on these projection CRT's? If so, have they lasted, &
how do they look after pix wise? Sony CRT's in direct-view units
look pale, & not so good after a boost, although most customers
don't complain, I wouldn't like to watch it after a boost.

I have a Sencore CR-70 rejuvinator, but it only has a socket # 3, # 4.
I haven't tried to boost them yet. I ask you guys, is a there a way to
"work around" the AKB problem? Iv'e seen info about adding resistors
to "tweak" the pix to stay on, even though it isn't as nice a pix, but
quite
watchable. Sky.

Thanks to all for your responses:

David: Is CRT rejuvenation a possible remedy for this problem?

Robert McPherson

wrote:
Thanks to all for your responses:

David: Is CRT rejuvenation a possible remedy for this problem?

Robert McPherson




You can try it if you've got a rejuvenator, there's nothing to lose, but
PTV tubes generally do not fair well for that.

Generally PTV tubes will not rejuvinate but the attempt will cause the
flakes to short out the gun.

Think about what rejuvination actually does. It blasts the build up
off the guns and into the picture tube. Some of it does not vaporize
but falls down. On a regular tube it typically won't lodge in the
guns. Due to the position of a ptv tube, it almost always falls down
into the guns and causes problems.

The best bet is to adjust the G2 voltages to the mid point between
where blinking occurs and retrace lines are visible, then readjust for
the best possible gray scale in the service menu. The set is and will
be on borrowed time and should be treated as such.

David

" bravely wrote to "All" (18 Nov 05 12:45:37)
--- on the heady topic of " Sony PTV Model # KP-46XBR25 Video blinking
on/off about once per se"

dk From: "
dk Xref: core-easynews sci.electronics.repair:348996


dk Generally PTV tubes will not rejuvinate but the attempt will cause the
dk flakes to short out the gun.

dk Think about what rejuvination actually does. It blasts the build up
dk off the guns and into the picture tube. Some of it does not vaporize
dk but falls down. On a regular tube it typically won't lodge in the
dk guns. Due to the position of a ptv tube, it almost always falls down
dk into the guns and causes problems.

dk The best bet is to adjust the G2 voltages to the mid point between
dk where blinking occurs and retrace lines are visible, then readjust for
dk the best possible gray scale in the service menu. The set is and will
dk be on borrowed time and should be treated as such.

dk David


An alternative is to raise the temperature of the cathode a tad. This
provokes more electron emission though it may shorten the heater life.
(But who really cares at that point!?) A safer way to do this is to
replace the typical series resistor with a NTC resistor. This protects
from the inrush but then applies a slighter higher voltage to the
heater as it warms up. The calculation of the right value to use isn't
too hard and the info can be had from many sources. If there isn't
enough voltage from the heater source, sometimes it is possible to
wind a couple of wire turns on the FBK core. Just be sure the
temperature isn't so high it melts something on the neck. Use just
enough temperature to bring back decent emission. This method can
sometimes get an extra couple years' life from a marginal cathode.

A*s*i*m*o*v

.... Engineers do it to maximum stress loads.

Good idea, Asimov. Thanks!

Robert

Good idea, Asimov. Thanks!

Robert