Red color predominant screen; even to Menu Screen – ABL section control voltage
do not change according to the scene brightness changes _ thick horizontal bars; rolling
downward and upward _ thin retrace lines along with picture – VIDEOCON- CTV14TP
Fault condition
ABL
[Automatic Brightness Limiter] voltage seems to be almost constant. The picture seems to be smeared, with excess
red tone, retrace lines even with menu screen. Instead of blue back-ground, it displays RED. Checked all the components at the ABL section, referring to its circuit
diagram. A zener diode connected to the
ABL track at the CRT base card was found leaky.
Changed the Zener
diode [9.1V]. ABL voltage became normal,
and began to change according to the intensity of the picture brightness, but,
the red color was excess.
Checked all
the thee cathode voltage at CRT base pins.
The voltage to red-cathode was found abnormal [much less – with a
difference of 25V with respect to other two [blue & green] cathodes. Checked all the video output transistors at
the CRT base card. Three of them. All are found OK, with meter check. De-soldered out the transistor [red drive]
and checked it out of circuit. There was
a slight short detected between collector and base to that transistor,
measuring it at MegOhm range. Desoldered
out the blue drive transistor from the CRT base card, and checked it. The same number, but did not show any leak
when measured at the same MegOhm range.
Replaced
the Red drive transistor with a new one of same number, and inserted the blue
drive transistor in place, and switched
ON the set.
Measured
all the three cathode voltages; and found normal. The color too has displayed well.
Faulty displays before repair. Color of the picture changes as the screen changes; due to absense of ABL control voltage.
After repair
These pictures might have some imperfections as all of it has been shot by my Mobile phone
Click on the pictures to Magnify
