Panasonic ctp-2780sf TV - bad brightness range

[davexnet02]

Hello,
we've had this TV for a few years, mainly my son watches it,
but we're all sharing it now since the "main" TV is being
repaired.
The brightness control seems to have a bad range.
Even with the brighness control set to maximum,
the dark and shadow area's of the picture are lost in
solid black. Clearly the black point is wrong.
However, on the other end, the "picture" control
seems to have plenty of energy producing a *very*
bright white point (if you set it too high).

Is there a sub-bright adjustment somewhere?
What about tweaking the "screen" control slightly?

Appreciate any info.
Dave

 

[ian_tech]

Adjust the screen adjustement before you get littles white lines .

 

[dkuhajda]

Sounds like a bad picture tube, simply worn out.
The brightness range indicates low emmision.
However, when you crank up the contrast and brightness together, the tube
gets overdriven and the bright areas bloom out over bright.

To test, simply turn the contrast up, set brightness to the middle, start
with color control at minimum, then turn it up all the way. If you see
color 'bleeding', 'smearing' off to the right of bright images, tube is
simply worn out from use. If it passes this test, there is some other
fault in the set that needs troubleshot and repaired.

David

 

[davexnet02]

Sounds like a bad picture tube, simply worn out.
The brightness range indicates low emmision.
However, when you crank up the contrast and brightness together, the tube
gets overdriven and the bright areas bloom out over bright.

To test, simply turn the contrast up, set brightness to the middle, start
with color control at minimum, then turn it up all the way. If you see
color 'bleeding', 'smearing' off to the right of bright images, tube is
simply worn out from use. If it passes this test, there is some other
fault in the set that needs troubleshot and repaired.

David

Thanks for the info - I'll give your test a try.
I've a feeling, that this Tv has always been like this,
but I could be wrong.
Dave

 

[davexnet02]

Thanks for the info - I'll give your test a try.
I've a feeling, that this Tv has always been like this,
but I could be wrong.
Dave

No sign of a bad tube. I opened up the TV today.
Seems to have manual adjustments for the common items,
so presumably this set doesn't have a secret service mode.

I located the "screen" control as well as "sub bright".
I put on the home theater setup disk and brought up the
brightness setup. Basically 10 shades of grey, with the instructions
being that the 7th level should be just illuminated.
With the TV the way it was, nothing on this screen was visible
at all. I turned the sub bright ever so slightly and the screen
appeared. Adjusted it so that the level was correctly illuminated
with the external brightness control set just below max.

Used the blue screen to adjust the color and tint
user controls. Job finished. One observation, this TV also
has manual controls for the RGB cut and drive. This Panasonic,
as seems to be typical, has a definite blue cast, both light and dark.
However, without any special equipment, I decided to leave these
controls alone for now. Now if somebody could just invent an
simple method for this greyscale adjustment...

Dave

 

[James Sweet]

Used the blue screen to adjust the color and tint
user controls. Job finished. One observation, this TV also
has manual controls for the RGB cut and drive. This Panasonic,
as seems to be typical, has a definite blue cast, both light and dark.
However, without any special equipment, I decided to leave these
controls alone for now. Now if somebody could just invent an
simple method for this greyscale adjustment...

Dave

You can get the grayscale reasonably close by comparing to a 6500K light
source. Many of the "daylight" compact fluorescent bulbs have a color
temperature of 6500K, they're harder to find than the usual warm 2700K lamps
but they are available.