Brightness problems on Panasonic TX-28ps1

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Sorry for longish post ...
bought a used Panasonic a few weeks back (TX-28ps1)...
Seemed ok for the first few days (oh oh!) ...
now on first switching on ... picture shows very bright
-sometimes almost white... if it gets too white it
seems to cause the TV to switch off into standby...
if not then after 10 minutes it settles down to a more normal
(perhaps slightly dark, overly contrasted?) picture...
which is watchable for hours
.... although occasionally flickers brighter before settling down
again.

Found service mode1 screen...
The one value that looks most odd is UG2 test

Ug2 Test shows
"Ug2 255 high" (rather than manual indicative value off "Ug2 130
O.K.")

Other values shown are
High 0920 0756 0787 (rather than manual indicative value 0902 0777
0864)
Low 0117 0132 0112 (rather than manual indicative value 0117 0132
0112)
Sub-Brightness 016 (rather than manual indicative value 003)


Could UG2 be the cause? Not sure what it is?
Or have I bought a duff TV?

Manual says....

To adjust Cutoff connect an oscilloscope to
the Blue cathode. Adjust "cutoff" value
using the "Yellow" and "Blue" buttons until
the black level is 160V +5V/-0V, press
"TV/AV" to store the value.
Remove the oscilloscope.
Select Ug2 adjustment and adjust the
screen VR until the display shows "O.K."

As I don't have an oscilloscope ... could I assume cutoff is ok and
carefully adjust the screen VR until the display shows "O.K." (rather
than high)
(I assume VR is basically an adjustment screw on one of the boards)?

Thanks for any help
AJ

 

[Meat Plow]

Sorry for longish post ...
bought a used Panasonic a few weeks back (TX-28ps1)...
Seemed ok for the first few days (oh oh!) ...
now on first switching on ... picture shows very bright
-sometimes almost white... if it gets too white it
seems to cause the TV to switch off into standby...
if not then after 10 minutes it settles down to a more normal
(perhaps slightly dark, overly contrasted?) picture...
which is watchable for hours
... although occasionally flickers brighter before settling down
again.

Found service mode1 screen...
The one value that looks most odd is UG2 test

Ug2 Test shows
"Ug2 255 high" (rather than manual indicative value off "Ug2 130
O.K.")

Other values shown are
High 0920 0756 0787 (rather than manual indicative value 0902 0777
0864)
Low 0117 0132 0112 (rather than manual indicative value 0117 0132
0112)
Sub-Brightness 016 (rather than manual indicative value 003)


Could UG2 be the cause? Not sure what it is?
Or have I bought a duff TV?

If the set worked ok and now doesn't it's unlikely to be an adjustment
especially if it shuts itself down. You could try to set the service mode
values to their default and see what happens, just write down what they
were before making the changes.

 

[Steve Roberts]

As I don't have an oscilloscope ... could I assume cutoff is ok and
carefully adjust the screen VR until the display shows "O.K." (rather
than high)
(I assume VR is basically an adjustment screw on one of the boards)?

Yeah, that's certainly what I would do in your situation.

Steve


The Doctor Who Restoration Team Website
http://www.restoration-team.co.uk

 

[sheldonstv]

check the rgb 2oov supply is present............