Please help in identifying TV picture fault.

[davexnet02]

Hello,
Before I get the Tech in, was wondering if anybody
has any insight as to what this problem may be..

My 1992 Sony kv27xbr35 has developed an unusual
picture problem. It's intermittent, sometimes
it's not there at all, the rest of the time it varies
in intensity, seems worse on a bright dynamic picture
where the contrast is higher.

It's basically alternating light and dark horizontal
lines, about 1/2 wide (approx) which seem to shimmer.

Here's a sample:
http://home.comcast.net/~davetest/capture.mpg (370kb)

Please note: the rainbow/diagonal effect is not a part
of the problem, but an artifact produced during the HI8 capture.

This fault appears regardless of the source,
just as likely to be dvd player, vcr or DBS.
Does it through the RF and video/s-video inputs.

Appreciate any feedback.
Dave

 

[Art]

Sounds as if the crt may be getting weak and the AKB circuit can no longer
keep up with the beam current demands. Is the symptom worse if the contrast
and brightness are at a higher than mid range setting and go away when both
settings are set quite a bit lower? If so then you either have a soft crt or
something in the bias circuitry to the crt going awry.

 

[davexnet02]

Sounds as if the crt may be getting weak and the AKB circuit can no longer
keep up with the beam current demands. Is the symptom worse if the contrast
and brightness are at a higher than mid range setting and go away when both
settings are set quite a bit lower? If so then you either have a soft crt or
something in the bias circuitry to the crt going awry.

The distortion in the picture is intermittent. I tried to produce an
mpeg of the problem. It's similar, but it doesn't do it justice
due to the limitation of the HI8 recording.

The distortion on the TV is shimmering horizontal lines, half
an inch wide, no tearing, no rainbow colors, no diagonal patterns.

It seems that when the "picture" control is turned down it
fades a little.


I eyeballed the screen up close and in the dark stripes, it seems as
if every other line in there is unlit. ie. it's pure black on the
screen.

Dave

 

[Jerry G.]

The only way that the tech is going to know what the brightness fault
is, he is going to have to check the G2 bias, and the biases to the CRT.
It is possible to have a bias fault to the CRT, a supply fault from the
G2 supply, general power supply faults, or a bad CRT to cause brightness
variations.

--

Jerry G.
======

Hello,
Before I get the Tech in, was wondering if anybody
has any insight as to what this problem may be..

My 1992 Sony kv27xbr35 has developed an unusual
picture problem. It's intermittent, sometimes
it's not there at all, the rest of the time it varies
in intensity, seems worse on a bright dynamic picture
where the contrast is higher.

It's basically alternating light and dark horizontal
lines, about 1/2 wide (approx) which seem to shimmer.

Here's a sample:
http://home.comcast.net/~davetest/capture.mpg (370kb)

Please note: the rainbow/diagonal effect is not a part
of the problem, but an artifact produced during the HI8 capture.

This fault appears regardless of the source,
just as likely to be dvd player, vcr or DBS.
Does it through the RF and video/s-video inputs.

Appreciate any feedback.
Dave

 

[davexnet02]

The only way that the tech is going to know what the brightness fault
is, he is going to have to check the G2 bias, and the biases to the CRT.
It is possible to have a bias fault to the CRT, a supply fault from the
G2 supply, general power supply faults, or a bad CRT to cause brightness
variations.

Thanks Jerry,
oddly enough the tech just rebuilt the power supply.
2 leaky diodes, 2 35v capacitors and a drive transformer.
To be fair to him, I had seen this once or twice before,
it was very low intensity, and it came and went.

But since the PS was fixed, it's back, and it's
much more vivid. The tech came to the house,
and off the top of his head didn't know what it was. He asked
me to leave it for a week or two to see if anything changes,
and to give him time to think about it.
Dave

 

[BWL]

Don't know how relavent this is, but a similar problem I found in a Mitsubishi
Projection unit was traced to a bad cap in the power supply