[TechAssist] Samsung TV, model TXJ2554 chassis K51A -black screen SAMS 4256

  • From: Gary McCartney <gary@xxxxxxxxxxx>
  • To: techassist@xxxxxxxxxxxxx
  • Date: Thu, 30 Jan 2003 14:32:53 -0500

This is a Samsung TXJ2554 chassis K51A. (SAMS 4256)
Turn set on, has sound but screen is black. Let it run and
nothing changes usually, but one time the picture popped on normal all
of a sudden. When turned on the next time, it had a black screen only
again. 
I turned the screen control all the way up and the picture
snapped in ok. Turned screen back down and the picture bloomed like
crazy. 
It went really bright like it was saturated with too much contrast.
Turned it back up to max. and picture was ok.
Measured G2 on CRT board. Had an even voltage range but seems low- went
from 76V low end to 276V high end. Disconnected CRT board and G2 voltage
acted the same. Then I changed the G2 disc capacitor on the CRT board
(.01uF 3kv). That didn't make any difference. I think flyback should put
out around 500V on G2 at high
end on most TVs, but it is only 276V. Is flyback defective?  Would The
blooming be a sour tube? Why would it bloom  when I turn the screen
down? Tapping on the tube neck doesn't make anything happen. R,G, B
cathodes measure around 68Vdc with normal picture (seems low, ?). With
blooming picture, I measure 33Vdc. With CRT socket removed, I read
191Vdc. The G1 pin measures approx. 0.4Vdc in any condition. So from
these measurements it looks as if the CRT is drawing too much current. 


Do I have a bad flyback or CRT, or both?  Does anyone have a schematic
with the dc voltages so I know if my readings are anywhere close to
normal- which I don't believe they are?
-- 




Gary McCartney

McCartney Electronics
7134 Fife Rd, RR 7
Guelph Ontario Canada N1H 6J4
Fax: (519)821-1530
email: gary (at) number63.ca

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