Darla.india (VU 3 NDV):
When power on the LCD TV, after 1 second the display will cut off. But the TV sound was normal
except no display only. The supply voltage to the inverter board was good and the inverter ON
signal from mainboard was present too. That’s mean the problem was on the inverter board or
CCFL lamps. After measured all suspected components on the inverter board, it seems that all
components were good. Since I do not have the CCFL Lamp Tester at the moment, i have used a
special method to test the CCFL lamps to check if they are working or not.
You need to be careful about this method because it could harm the components in the inverter
board. This method is called as “Bypass Inverter Protection” because it could let the inverter
board to continue provides high voltage to the CCFL lamps. In otheprotectionr words, this method will
let you know if either the CCFL lamps or the inverter board problem that had caused the LCD
TV to shut down after a second. Further inspection I found that this LCD TV was using OZ9938
IC as inverter IC. If you refer to the pin 3 in the diagram below you could see the pin
marking was “Timer” and the description as “timing capacitor to set striking time and
shutdown delay time”. This means that external capacitor will make the decision to “ON”
the CCFL lamps timing. If the voltage value reach on their setting voltages and the lamps
still not start-up, then the OZ9938 will stop working and lock up.
Now, when you short pin 3 of OZ9938 IC to ground, it will temporary cancel the backlight
system cut off protection feature and the LCD TV can be turned on with good display
without shutting down anymore. Look at the screen now to see if there are any black/dark
bar area and make sure the brightness are even in all angles. If the display and brightness
are good then this means the backlights are working fine and the problem is in the
inverter board. If you could see dark/black area then this means one of the LCD
backlight have problem. Do not turn on the LCD TV for too long for safety purposes.
When power on the LCD TV, after 1 second the display will cut off. But the TV sound was normal
except no display only. The supply voltage to the inverter board was good and the inverter ON
signal from mainboard was present too. That’s mean the problem was on the inverter board or
CCFL lamps. After measured all suspected components on the inverter board, it seems that all
components were good. Since I do not have the CCFL Lamp Tester at the moment, i have used a
special method to test the CCFL lamps to check if they are working or not.
You need to be careful about this method because it could harm the components in the inverter
board. This method is called as “Bypass Inverter Protection” because it could let the inverter
board to continue provides high voltage to the CCFL lamps. In otheprotectionr words, this method will
let you know if either the CCFL lamps or the inverter board problem that had caused the LCD
TV to shut down after a second. Further inspection I found that this LCD TV was using OZ9938
IC as inverter IC. If you refer to the pin 3 in the diagram below you could see the pin
marking was “Timer” and the description as “timing capacitor to set striking time and
shutdown delay time”. This means that external capacitor will make the decision to “ON”
the CCFL lamps timing. If the voltage value reach on their setting voltages and the lamps
still not start-up, then the OZ9938 will stop working and lock up.
Now, when you short pin 3 of OZ9938 IC to ground, it will temporary cancel the backlight
system cut off protection feature and the LCD TV can be turned on with good display
without shutting down anymore. Look at the screen now to see if there are any black/dark
bar area and make sure the brightness are even in all angles. If the display and brightness
are good then this means the backlights are working fine and the problem is in the
inverter board. If you could see dark/black area then this means one of the LCD
backlight have problem. Do not turn on the LCD TV for too long for safety purposes.
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