Troubleshooting fault when TV first turned on
 

Hello all,
when I first turn my TV on, I get a bright blue screen with
retrace lines. Voltages are as follows:
red 200
green 200
blue 75
G2 520

After about three minutes, the normal picture appears.
Voltages are now:
red 175
green 175
blue 160
G2 440

What are the possibilities? I thought possible
loose / bad connection but why would it correct itself
after 3 minutes?

regards,
Dave

Check voltages again with the board unplugged from the picture tube. If
voltages are now normal on the blue (160v) then the tube is shorted.

On 25 Jan 2005 12:26:04 -0800, "
wrote:

Check voltages again with the board unplugged from the picture tube. If
voltages are now normal on the blue (160v) then the tube is shorted.
Hello, thanks for this suggestion.
However, the result (apparently) is not a tube short.
The voltage continued to read low ( 80 V) on the blue
cathode even with the crt board disconnected.
Red and green both 200 V approx - as before.

I dug around a little more. I suspect the vertical
y/c jungle board. This board is soldered to the
main A board. I say this because when I tapped the top
of this board, it affected the blue screen, it cleared to
black and the normal picture appeared for a second.

It's strange, because as I said, if I wait 2 or 3 minutes,
the normal, good picture returns by otself.

Is this board even available anymore? Trying to find a
problem in here is going to be impossible.
TV is Sony 1992 kv27-xbr35.

Thanks for any info.
Dave

On Wed, 26 Jan 2005 10:26:43 -0800, Jamie
wrote:

wrote:

Check voltages again with the board unplugged from the picture tube. If
voltages are now normal on the blue (160v) then the tube is shorted.

is that slightly dangerous with the Anode alive and well plugged into
the CRT ?
I think that doing it may have made things worse.
Now the TV is blue all the time.
Spraying the crt board with a cooler doesn't do anything.

I think you're right, I held the crt board very carefull by the
edges, and I got the sense that my hair was starting to stand
on end from a static charge. It does seem dangerous
and as I said possibly made things worse.

I think the y/c jungle board is bad and if that's so, I'll probably
have to junk the set.
Dave

davexnet02 wrote:

Hello all,
when I first turn my TV on, I get a bright blue screen with
retrace lines. Voltages are as follows:
red 200
green 200
blue 75
G2 520

After about three minutes, the normal picture appears.
Voltages are now:
red 175
green 175
blue 160
G2 440

What are the possibilities? I thought possible
loose / bad connection but why would it correct itself
after 3 minutes?

regards,
Dave
bad picture tube.
bad driver transistor.
solder joint crack that is thermo connecting.
bad CRT plug..
or some other misc conponent on the board that drives the CRT.

It certainly sounds like an intermittent Heater-to-Cathode (Blue in this
case) short internal to the CRT. I have seen many like it in all brands...
If you take the palm of your hand, and slap the face of the tube firmly, it
probably goes away? As the heaters in the CRT heat up and cool down,
peeling, corroded cathodes in the CRT can come in contact with each other
providing a path to ground (one side of the heater is usually ground. )

If this is CONFIRMED to be the case, you have a couple of options:

1.)Replace the CRT.

2.)Junk it

3.) Use a CRT tester / rejuvenator with the "remove shorts" feature
like a B&K, etc. (Doesn't ALWAYS work...)

4. Isolate the heaters to the CRT.

I have a favorite method of doing this on those "last ditch effort"
units that involves desoldering the heater pins at the CRT socket, which
disconnects them from ground, and running a single piece of wire to the
flyback transformer, where I "loop" a single wrap of wire around the exposed
ferrite core of the transformer. This will tap the flyback with a high
current, low voltage source to heat the filaments, while providing complete
isolation from ground. (It will allow the DC voltage to simply "float" at
whichever cathode is shorting to it internal to the CRT... ) -If the blue
cathode wants to short to the filaments, the filaments simply float up to
+200V on both sides, the Cathode voltage never changes (no drain on it) so
you do not see any effects on the picture....an old trick from way
back....'Course I am assuming you have the technical skills and literature
to verify whether or not this is your problem and find the correct pins on
the CRT, etc. etc. etc...etc........Also note that this 'fix" only works if
ONE cathode is shorting to the heaters, any more than that, and you'll get
crosstalk between the two or more shorting cathodes, distorting the color,
by driving each other with the same waveform.


"davexnet02" wrote in message
...
Hello all,
when I first turn my TV on, I get a bright blue screen with
retrace lines. Voltages are as follows:
red 200
green 200
blue 75
G2 520

After about three minutes, the normal picture appears.
Voltages are now:
red 175
green 175
blue 160
G2 440

What are the possibilities? I thought possible
loose / bad connection but why would it correct itself
after 3 minutes?

regards,
Dave

On Fri, 28 Jan 2005 03:29:58 GMT, "Phil Bowser"
wrote:

It certainly sounds like an intermittent Heater-to-Cathode (Blue in this
case) short internal to the CRT. I have seen many like it in all brands...
If you take the palm of your hand, and slap the face of the tube firmly, it
probably goes away? As the heaters in the CRT heat up and cool down,
peeling, corroded cathodes in the CRT can come in contact with each other
providing a path to ground (one side of the heater is usually ground. )

If this is CONFIRMED to be the case, you have a couple of options:

1.)Replace the CRT.

2.)Junk it

3.) Use a CRT tester / rejuvenator with the "remove shorts" feature
like a B&K, etc. (Doesn't ALWAYS work...)

4. Isolate the heaters to the CRT.

I have a favorite method of doing this on those "last ditch effort"
units that involves desoldering the heater pins at the CRT socket, which
disconnects them from ground, and running a single piece of wire to the
flyback transformer, where I "loop" a single wrap of wire around the exposed
ferrite core of the transformer. This will tap the flyback with a high
current, low voltage source to heat the filaments, while providing complete
isolation from ground. (It will allow the DC voltage to simply "float" at
whichever cathode is shorting to it internal to the CRT... ) -If the blue
cathode wants to short to the filaments, the filaments simply float up to
+200V on both sides, the Cathode voltage never changes (no drain on it) so
you do not see any effects on the picture....an old trick from way
back....'Course I am assuming you have the technical skills and literature
to verify whether or not this is your problem and find the correct pins on
the CRT, etc. etc. etc...etc........Also note that this 'fix" only works if
ONE cathode is shorting to the heaters, any more than that, and you'll get
crosstalk between the two or more shorting cathodes, distorting the color,
by driving each other with the same waveform.
Hi Phil,
thanks for the info... The whole project is probably moot now.
In an error of judgement, I turned on the TV with the CRT board
pulled off the tube in an attempt to measure some voltages.

I think the static build up around the tube neck ( I'm sure
my hair was starting to stand up) damaged something -
(the crt board itself ? )
Now the TV is bright blue continuously.
It's one step closer to junking, but of course,
still appreciate any info. At least, myself
and perhaps others, have learned something and
not make the same mistake again.
regards,
Dave

da_test writes:

On Fri, 28 Jan 2005 03:29:58 GMT, "Phil Bowser"
wrote:

It certainly sounds like an intermittent Heater-to-Cathode (Blue in this
case) short internal to the CRT. I have seen many like it in all brands...
If you take the palm of your hand, and slap the face of the tube firmly, it
probably goes away? As the heaters in the CRT heat up and cool down,
peeling, corroded cathodes in the CRT can come in contact with each other
providing a path to ground (one side of the heater is usually ground. )

If this is CONFIRMED to be the case, you have a couple of options:

1.)Replace the CRT.

2.)Junk it

3.) Use a CRT tester / rejuvenator with the "remove shorts" feature
like a B&K, etc. (Doesn't ALWAYS work...)

4. Isolate the heaters to the CRT.

I have a favorite method of doing this on those "last ditch effort"
units that involves desoldering the heater pins at the CRT socket, which
disconnects them from ground, and running a single piece of wire to the
flyback transformer, where I "loop" a single wrap of wire around the exposed
ferrite core of the transformer. This will tap the flyback with a high
current, low voltage source to heat the filaments, while providing complete
isolation from ground. (It will allow the DC voltage to simply "float" at
whichever cathode is shorting to it internal to the CRT... ) -If the blue
cathode wants to short to the filaments, the filaments simply float up to
+200V on both sides, the Cathode voltage never changes (no drain on it) so
you do not see any effects on the picture....an old trick from way
back....'Course I am assuming you have the technical skills and literature
to verify whether or not this is your problem and find the correct pins on
the CRT, etc. etc. etc...etc........Also note that this 'fix" only works if
ONE cathode is shorting to the heaters, any more than that, and you'll get
crosstalk between the two or more shorting cathodes, distorting the color,
by driving each other with the same waveform.
Hi Phil,
thanks for the info... The whole project is probably moot now.
In an error of judgement, I turned on the TV with the CRT board
pulled off the tube in an attempt to measure some voltages.

I think the static build up around the tube neck ( I'm sure
my hair was starting to stand up) damaged something -
(the crt board itself ? )
Now the TV is bright blue continuously.
It's one step closer to junking, but of course,
still appreciate any info. At least, myself
and perhaps others, have learned something and
not make the same mistake again.

So you're going to give up because maybe a 10 cent part got
blown?

Think of it as an additional challenge! :)

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On 04 Feb 2005 08:41:28 -0500, Sam Goldwasser
wrote:

da_test writes:

I think the static build up around the tube neck ( I'm sure
my hair was starting to stand up) damaged something -
(the crt board itself ? )
Now the TV is bright blue continuously.
It's one step closer to junking, but of course,
still appreciate any info. At least, myself
and perhaps others, have learned something and
not make the same mistake again.

So you're going to give up because maybe a 10 cent part got
blown?

Think of it as an additional challenge! :)

--- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/
Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/
+Lasers | Sam's Laser FAQ: http://repairfaq.ece.drexel.edu/sam/lasersam.htm
| Mirror Sites: http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html

Hello Sam,
Point taken the 10 cent part.
I took a look at the components on the crt board,
there are 15 transistors, some ceramic and elect capacitors,
a few resistors, diodes and inductors.

I don't know enough enough about what might have happened
to know where to start. What does the static damage?
All transistors?
What's the best strategy? pull all transistors and attempt to
test them? Just replace them all? Anything else?
regards,
Dave

On Fri, 04 Feb 2005 08:50:58 -0800, da_test
wrote:

On 04 Feb 2005 08:41:28 -0500, Sam Goldwasser
So you're going to give up because maybe a 10 cent part got
blown?

Think of it as an additional challenge! :)

--- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/
Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/
+Lasers | Sam's Laser FAQ: http://repairfaq.ece.drexel.edu/sam/lasersam.htm
| Mirror Sites: http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html

Hello Sam,
Point taken the 10 cent part.
I took a look at the components on the crt board,
there are 15 transistors, some ceramic and elect capacitors,
a few resistors, diodes and inductors.

I don't know enough enough about what might have happened
to know where to start. What does the static damage?
All transistors?
What's the best strategy? pull all transistors and attempt to
test them? Just replace them all? Anything else?
regards,
Dave
I found the datasheet on transistor 2sc2611.
They're the 3 transistors on the crt board attached to the
big heat sinks. The factsheet confirmed static sensitivy.

My local electronics store was able to supply me with
3 NTE157 as replacements for $1.97 each.
Not quite 10 cents Sam, but close !

TV is working again, good picture.
thanks all,
Dave