Hello all --

I have a Sony KV-32XBR48 that was manufactured in October, 1997. The
problem is that the picture blinks on and off at about a one second rate.
The audio is constant, and the problem happens whether the video source is
from the tuner or a video input. One other symptom is that it seems to me
that the time for the picture to come on the first time is much longer than
it used to be, and when the picture first comes on, it only stays on for a
brief time, and stays off for quite a while. As the set warms up, it gets
to about one second on, and one second off.

I have spent a fair amount of time looking at the set, and what I see is
that the video signal looks good going into IC351 which is a Sony CXA2025 Y
chroma/jungle IC. The RGB video drive signals out of this chip change
directly as the picture blinks on and off. One other thing is that pin 26
of this same chip changes with the picture blinking on and off. This seems
to make sense since it appears to be essentially a flyback transformer
current sense. Both the picture on and picture off voltages at pin 26 are
much higher than the schematic from SAMS indicates it should be. The only
way I see for the voltage to get lower is to draw more current through the
flyback. The voltage I see is about 9 volts when the picture is off, and
about 8 volts when the picture is on. (I can get more precise readings if
that is helpful.) The SAMS predicted voltage at that point is 1.6 volts.

I have checked power supply voltages, and they seem reasonable. None of
them fluctuates with the picture on/off. I have resoldered the joints at
the flyback transformer, but no others.

Any tips at this point would be greatly appreciated.

Thanks in advance

Dave Miller
Tucson, AZ

Your picture tube is weak. You can turn up the screen control slightly
and the set will work, but the picture quality will be poor because of
the weak picture tube.
Dave Miller wrote:
Hello all --

I have a Sony KV-32XBR48 that was manufactured in October, 1997. The

problem is that the picture blinks on and off at about a one second
rate.
The audio is constant, and the problem happens whether the video
source is
from the tuner or a video input. One other symptom is that it seems
to me
that the time for the picture to come on the first time is much
longer than
it used to be, and when the picture first comes on, it only stays on
for a
brief time, and stays off for quite a while. As the set warms up, it
gets
to about one second on, and one second off.

I have spent a fair amount of time looking at the set, and what I see
is
that the video signal looks good going into IC351 which is a Sony
CXA2025 Y
chroma/jungle IC. The RGB video drive signals out of this chip
change
directly as the picture blinks on and off. One other thing is that
pin 26
of this same chip changes with the picture blinking on and off. This
seems
to make sense since it appears to be essentially a flyback
transformer
current sense. Both the picture on and picture off voltages at pin
26 are
much higher than the schematic from SAMS indicates it should be. The
only
way I see for the voltage to get lower is to draw more current
through the
flyback. The voltage I see is about 9 volts when the picture is off,
and
about 8 volts when the picture is on. (I can get more precise
readings if
that is helpful.) The SAMS predicted voltage at that point is 1.6
volts.

I have checked power supply voltages, and they seem reasonable.
None of
them fluctuates with the picture on/off. I have resoldered the
joints at
the flyback transformer, but no others.

Any tips at this point would be greatly appreciated.

Thanks in advance

Dave Miller
Tucson, AZ

The sure fire fix is to replace the weak picture tube. Common on Sony
sets with the AKB circuit. A slight increase in G2 voltage will buy
some time, but it is pretty much time to start shopping for a new set.

Do a google groups archive search here for Sony blanking, AKB, blinking
video, etc.

David

Dave Miller wrote:
Hello all --

I have a Sony KV-32XBR48 that was manufactured in October, 1997. The

problem is that the picture blinks on and off at about a one second
rate.
The audio is constant, and the problem happens whether the video
source is
from the tuner or a video input. One other symptom is that it seems
to me
that the time for the picture to come on the first time is much
longer than
it used to be, and when the picture first comes on, it only stays on
for a
brief time, and stays off for quite a while. As the set warms up, it
gets
to about one second on, and one second off.

I have spent a fair amount of time looking at the set, and what I see
is
that the video signal looks good going into IC351 which is a Sony
CXA2025 Y
chroma/jungle IC. The RGB video drive signals out of this chip
change
directly as the picture blinks on and off. One other thing is that
pin 26
of this same chip changes with the picture blinking on and off. This
seems
to make sense since it appears to be essentially a flyback
transformer
current sense. Both the picture on and picture off voltages at pin
26 are
much higher than the schematic from SAMS indicates it should be. The
only
way I see for the voltage to get lower is to draw more current
through the
flyback. The voltage I see is about 9 volts when the picture is off,
and
about 8 volts when the picture is on. (I can get more precise
readings if
that is helpful.) The SAMS predicted voltage at that point is 1.6
volts.

I have checked power supply voltages, and they seem reasonable.
None of
them fluctuates with the picture on/off. I have resoldered the
joints at
the flyback transformer, but no others.

Any tips at this point would be greatly appreciated.

Thanks in advance

Dave Miller
Tucson, AZ

"Dave Miller" wrote in message
...

Hello all --

I have a Sony KV-32XBR48 that was manufactured in October, 1997. The
problem is that the picture blinks on and off at about a one second rate.
The audio is constant, and the problem happens whether the video source is
from the tuner or a video input. One other symptom is that it seems to me
that the time for the picture to come on the first time is much longer
than it used to be, and when the picture first comes on, it only stays on
for a brief time, and stays off for quite a while. As the set warms up,
it gets to about one second on, and one second off.

I have spent a fair amount of time looking at the set, and what I see is
that the video signal looks good going into IC351 which is a Sony CXA2025
Y chroma/jungle IC. The RGB video drive signals out of this chip change
directly as the picture blinks on and off. One other thing is that pin 26
of this same chip changes with the picture blinking on and off. This
seems to make sense since it appears to be essentially a flyback
transformer current sense. Both the picture on and picture off voltages
at pin 26 are much higher than the schematic from SAMS indicates it should
be. The only way I see for the voltage to get lower is to draw more
current through the flyback. The voltage I see is about 9 volts when the
picture is off, and about 8 volts when the picture is on. (I can get more
precise readings if that is helpful.) The SAMS predicted voltage at that
point is 1.6 volts.

I have checked power supply voltages, and they seem reasonable. None of
them fluctuates with the picture on/off. I have resoldered the joints at
the flyback transformer, but no others.

Any tips at this point would be greatly appreciated.

Thanks in advance

Dave Miller
Tucson, AZ
Bad picture tube can cause your problem. Sony's early models would blank
the video until the beam current from the tree tubes balanced (for white
balance). IF the beam current never balances then you never have any
picture.

In this model, if the CRT is going defective, this effect will occur. It
is a type of protection for the high voltage, and X-Ray emissions.
Changing the CRT should fix the fault, but is not a feasible option.

--

Jerry G.
======

"Dave Miller" wrote in message
...

Hello all --

I have a Sony KV-32XBR48 that was manufactured in October, 1997. The
problem is that the picture blinks on and off at about a one second
rate.
The audio is constant, and the problem happens whether the video source
is
from the tuner or a video input. One other symptom is that it seems to
me
that the time for the picture to come on the first time is much longer
than
it used to be, and when the picture first comes on, it only stays on for
a
brief time, and stays off for quite a while. As the set warms up, it
gets
to about one second on, and one second off.

I have spent a fair amount of time looking at the set, and what I see is
that the video signal looks good going into IC351 which is a Sony
CXA2025 Y
chroma/jungle IC. The RGB video drive signals out of this chip change
directly as the picture blinks on and off. One other thing is that pin
26
of this same chip changes with the picture blinking on and off. This
seems
to make sense since it appears to be essentially a flyback transformer
current sense. Both the picture on and picture off voltages at pin 26
are
much higher than the schematic from SAMS indicates it should be. The
only
way I see for the voltage to get lower is to draw more current through
the
flyback. The voltage I see is about 9 volts when the picture is off,
and
about 8 volts when the picture is on. (I can get more precise readings
if
that is helpful.) The SAMS predicted voltage at that point is 1.6
volts.

I have checked power supply voltages, and they seem reasonable. None
of
them fluctuates with the picture on/off. I have resoldered the joints
at
the flyback transformer, but no others.

Any tips at this point would be greatly appreciated.

Thanks in advance

Dave Miller
Tucson, AZ

Thanks to all for the replies.

Let me see if I understand this: when a CRT starts getting weak, the
resistance in it goes up, so it doesn't draw as much current from the
flyback as the compensation circuit thinks it should. Since it can't raise
the tube voltage anymore without risk of x-rays, it shuts down. Is that
sort of correct?

I appreciate the help. It is too damn bad, because that was a really nice
TV in its day.

Oh well

Dave Miller


"Jerry G." wrote in message
...
In this model, if the CRT is going defective, this effect will occur. It
is a type of protection for the high voltage, and X-Ray emissions.
Changing the CRT should fix the fault, but is not a feasible option.

--

Jerry G.
======

"Dave Miller" wrote in message
...

Hello all --

I have a Sony KV-32XBR48 that was manufactured in October, 1997. The
problem is that the picture blinks on and off at about a one second
rate.
The audio is constant, and the problem happens whether the video source
is
from the tuner or a video input. One other symptom is that it seems to
me
that the time for the picture to come on the first time is much longer
than
it used to be, and when the picture first comes on, it only stays on for
a
brief time, and stays off for quite a while. As the set warms up, it
gets
to about one second on, and one second off.

I have spent a fair amount of time looking at the set, and what I see is
that the video signal looks good going into IC351 which is a Sony
CXA2025 Y
chroma/jungle IC. The RGB video drive signals out of this chip change
directly as the picture blinks on and off. One other thing is that pin
26
of this same chip changes with the picture blinking on and off. This
seems
to make sense since it appears to be essentially a flyback transformer
current sense. Both the picture on and picture off voltages at pin 26
are
much higher than the schematic from SAMS indicates it should be. The
only
way I see for the voltage to get lower is to draw more current through
the
flyback. The voltage I see is about 9 volts when the picture is off,
and
about 8 volts when the picture is on. (I can get more precise readings
if
that is helpful.) The SAMS predicted voltage at that point is 1.6
volts.

I have checked power supply voltages, and they seem reasonable. None
of
them fluctuates with the picture on/off. I have resoldered the joints
at
the flyback transformer, but no others.

Any tips at this point would be greatly appreciated.

Thanks in advance

Dave Miller
Tucson, AZ

Not exactly. Sony uses an AKB (auto-kine-bias) which during the
vertical blanking interval sends out a red line, green line, and a blue
line. The AKB circuit senses the current and as long as all three are
close and within specifications for the circuit, the video is unblanked
when the tube is warmed up. By blanking the video during the warm up
time it prevents the 'stripping' of the cathodes that happens in vacuum
tubes when full cathode voltage is applied before the tubes heat up all
the way. This circuit also fine adjusts the tube bias for each color
to keep the color temperature close to correct over the life (useful
life) of the tube.

The problem you have is either one of two:
1. One of the guns is significantly weaker than the other two, making
the AKB circuit not see the tube within specifications.
2. All three guns are weak causing the blanking.

If you have access to a good o'scope, you can sync the scope off the
vertical blanking pulse and monitor the AKB line with the other
channel. With the tv totally cold, turn it on and watch the three akb
return pulses come up. You will likely see one of the guns come up
much slower than the other two.

BTW the reason the video blinks is that with no video on screen, the
cathode current makes it just inside the window to unblank the video.
As soon as the video comes on, the sudden drop in cathode current
during the sense scan line drops below specification and the video
again blanks out. This is why a slight increase of G2 voltage will
compensate for this for a time as it tends to average out the current
draw between blanked video and un-blanked video, but it also washes out
the picture some.

I see. I do have a good scope, I will look at those signals. It also looks
like you could get a good idea of those voltages by looking at the RGB
sample and hold capacitors on pins 19, 21, and 23.

When a gun is weak, does that mean that it can't drive the current for that
color effectively any more? I am still trying to understand the excessive
voltage at the "ABL IN VCCOMP" pin. (Pin 26). I get about 9 volts when the
picture is off, and about 8 volts when it is on.

The way I understand the circuit, the voltage at pin 26 will be about 11V if
no current is going through the secondary of the flyback transformer. As
current flows to the CRT anode, it is drawn from this node and the voltage
is reduced. This is why I keep asking about tube current. Here are the pin
summary for pin 26, and a piece of descriptive narrative about the ABL
function. Sorry to keep on about this, but to me understanding it is even
more satisfying than fixing it.

ABL control signal input and VSAW high voltage fluctuation compensation
signal input. High voltage compensation has linear control characteristics
for the pin voltage range of about 3V to 1V. ABL does not operate when the
pin voltage is 9 [V], and operates with increasing strength as the voltage
becomes lower than 9 [V].

The voltage applied to Pin 26 (ABLIN) is compared with the internal
reference voltage, integrated by the capacitor which is connected to Pin 27,
and performs picture control and brightness control. In order to adjust the
white balance (black balance), this IC has a drive control function which
adjusts the gain between the RGB outputs and a cut-off control function
which adjusts the DC level between the RGB outputs.



Thanks again for your help. Your expertise is greatly appreciated.



Dave Miller






wrote in message
oups.com...
Not exactly. Sony uses an AKB (auto-kine-bias) which during the
vertical blanking interval sends out a red line, green line, and a blue
line. The AKB circuit senses the current and as long as all three are
close and within specifications for the circuit, the video is unblanked
when the tube is warmed up. By blanking the video during the warm up
time it prevents the 'stripping' of the cathodes that happens in vacuum
tubes when full cathode voltage is applied before the tubes heat up all
the way. This circuit also fine adjusts the tube bias for each color
to keep the color temperature close to correct over the life (useful
life) of the tube.

The problem you have is either one of two:
1. One of the guns is significantly weaker than the other two, making
the AKB circuit not see the tube within specifications.
2. All three guns are weak causing the blanking.

If you have access to a good o'scope, you can sync the scope off the
vertical blanking pulse and monitor the AKB line with the other
channel. With the tv totally cold, turn it on and watch the three akb
return pulses come up. You will likely see one of the guns come up
much slower than the other two.

BTW the reason the video blinks is that with no video on screen, the
cathode current makes it just inside the window to unblank the video.
As soon as the video comes on, the sudden drop in cathode current
during the sense scan line drops below specification and the video
again blanks out. This is why a slight increase of G2 voltage will
compensate for this for a time as it tends to average out the current
draw between blanked video and un-blanked video, but it also washes out
the picture some.

wrote in message
oups.com...
The sure fire fix is to replace the weak picture tube. Common on Sony
sets with the AKB circuit. A slight increase in G2 voltage will buy
some time, but it is pretty much time to start shopping for a new set.

Oh GREAT! I just posted a message about this same problem with my Sony
KV-35S65 model.

Arggggggggh, wonderful.

I have the repair people coming tomorrow (later today afternoon) to pick up
my Sony. Time to call them up to cancel the pickup first thing in the
morning and then talk to sony about this.

-- Papo

"Jeff Rigby" wrote in message
...


Bad picture tube can cause your problem. Sony's early models would blank
the video until the beam current from the tree tubes balanced (for white
balance). IF the beam current never balances then you never have any
picture.

Would you infer that Sony was aware of this flaw?

This happen with my set after the first year, the flyback transformer was
replaced,
but now after 4.5 years out of warranty now, it is happening again. Before,
it would blackout forever. Today, it is a 2-3 second blackout sequence.

What is bothering me though is this:

The problem started to act up again around September, 2004. As long as we
didn't turn off the TV, it all seem fine. But in December, it began to go
totally black. Unplugging it, waiting 30 seconds, etc, seen to fix it.
We were in the process of moving to a new home, so we wanted to get settled
first before addressing the issue. At the new home, we turned it on and it
was working again for the entire month of January, but we didn't turn off
the tv.

Now, for the past week or so, it started to go black again, but this time
with the 2-3 second cycle.

So what happen during the move? Did we have a loose part maybe? Or it just
a bad tube period?

I have an urge of knocking it around to see what happens g

I set up the scope, and it looks like the red gun is indeed failing. It has
the highest drive signal, and the lowest current. When I increase G2 a tiny
bit, the picture stabilizes like you suggest. When I watch it on the scope,
I see that increasing G2 decreases the current draw of B and G while leaving
R unchanged. So you are exactly right on.

It seems to me that there are two possible ways to cheat the system on this
one. One is that I could add a high value resistor (Maybe 1 to 5 megohms)
between the 200V supply and the output of the red video drive chip
(Conveniently the pins in question, 6 and 8, are about the distance of a
surface mount resistor apart). This would flow some extra current into the
output and might make it happy. The second way to cheat would be lower the
value of the series resistor between the IK output pin on the red video
driver and the IKB buffer. If either of these techniques worked, I might be
able to adjust the color back in with normal controls, and not get the
"washout" of using the G2 adjust.

Worth a try??

Thanks

Dave Miller
wrote in message
oups.com...
Not exactly. Sony uses an AKB (auto-kine-bias) which during the
vertical blanking interval sends out a red line, green line, and a blue
line. The AKB circuit senses the current and as long as all three are
close and within specifications for the circuit, the video is unblanked
when the tube is warmed up. By blanking the video during the warm up
time it prevents the 'stripping' of the cathodes that happens in vacuum
tubes when full cathode voltage is applied before the tubes heat up all
the way. This circuit also fine adjusts the tube bias for each color
to keep the color temperature close to correct over the life (useful
life) of the tube.

The problem you have is either one of two:
1. One of the guns is significantly weaker than the other two, making
the AKB circuit not see the tube within specifications.
2. All three guns are weak causing the blanking.

If you have access to a good o'scope, you can sync the scope off the
vertical blanking pulse and monitor the AKB line with the other
channel. With the tv totally cold, turn it on and watch the three akb
return pulses come up. You will likely see one of the guns come up
much slower than the other two.

BTW the reason the video blinks is that with no video on screen, the
cathode current makes it just inside the window to unblank the video.
As soon as the video comes on, the sudden drop in cathode current
during the sense scan line drops below specification and the video
again blanks out. This is why a slight increase of G2 voltage will
compensate for this for a time as it tends to average out the current
draw between blanked video and un-blanked video, but it also washes out
the picture some.

The cheats really don't work well.
You can try, a soft crt restore like that on some of the newer Sencore
rejuvinator/crt testers on just the red gun. The key is to try and get
them balanced close enough to give you some more time.

Lets see, the flyback failure even though you would lose video, you
were actually losing high voltage, hence the blank screen. That was
and is a totally different failure than what you have now, which is a
worn out picture tube.

Given that you acheived a good life of 4.5 years out of the tube, video
blanking is not uncommon. It is possible that when the flyback was
replaced, the screen voltage was not quite adjusted properly and the
G2/screen voltage needs readjusted. A mis-adjusted G2 voltage will
give the same symptom over time as a weak picture tube.

If the tv were run for 12 hours a day average for 4.5 years, that is
20,000 hours which is the typical life of a picture tube.

No sense having the tv picked up. The screen voltage can be adjusted
per the service manual in home. The only thing that is needed is a
good o-scope and an isolation transformer. It can be adjusted by eye,
and a multi-meter if the tech has enough experience with doing that
adjustment on a Sony set.