Solved! Sony bravia kdl 46nx700 dim screen issue

[jimbo-bob]

Hi everyone,

I have a Sony bravia kdl 46nx700. It turns on, but the screen is awfully dim.
Things I have tried:

1. Went into settings and increased the brightness and contrast. Screen did not change at all.
2. Went into settings and made sure any auto brightness settings and limit is turned off. Did not see any difference again even after playing with brightness and contrast.
3. Did a factory reset. Again no change. Then repeated the steps above. No change.

At this point I think with myself that this is a hardware problem. Since my tv does not have any warranty, I decide to open it up and have a look:

1. There are no signs of blown capacitors or resistors or diods etc.
2. I decided to measure the voltages on the pins going out to TCON board and the motherboard from the power board:

When the tv is on (image on screen):

TCON-ON	3.3V
TCON VCC 12V	12.64V
DIMMER-DC	3.31V
DIMMER	1.659V
BL-ON	3.05V
BL-ERR	2.4mV
REG12V	12.66V
REG12V	12.66V
REG12V-GND	7mV
REG12V-GND	7mV
AUDIO12V-GND	10.8mV
AUDIO12V	12.7V
POWER-ON	3.29V
AC OFF-DET	3.34V
STBY 3.3	3.34V

When tv is off (power button is pressed and there is no image on screen):

TCON-ON	0
TCON VCC 12V	1mV
DIMMER-DC	4.7mV
DIMMER	4.9mV
BL-ON	3.1mV
BL-ERR	5.3mV
REG12V	12.69V
REG12V	12.69V
REG12V-GND	3.6mV
REG12V-GND	3.6mV
AUDIO12V-GND	5.6mV
AUDIO12V	12.71V
POWER-ON	3.3V
AC OFF-DET	3.35V
STBY 3.3	3.35V

So my questions are:

1. Where does one find the voltage rating info for these pins? I came across manuals, but they only has schematics with no voltage info.
2. I am bit suspicious about the DIM pin having ~ 1.7V. Is that meant to be the case?

Any help is appreciated and I am happy to provide more information.

 

[hang-the-9]

May need a new backlight, which is pretty much impossible to buy for TVs, and is usually cheaper to just replace it. New 55" screens are pretty cheap, and used ones that are working normally even more so. I bought a 49" TV for about $100 a year ago.

 

[jimbo-bob]

May need a new backlight, which is pretty much impossible to buy for TVs, and is usually cheaper to just replace it. New 55" screens are pretty cheap, and used ones that are working normally even more so. I bought a 49" TV for about $100 a year ago.

If the backlight is dead it would be quite unfortunate. Is there any way for me to make sure it is the backlight and not something on the circuit boards? I mean I can see all the lights turn on from the back of the tv. Very rarely, the brightness becomes normal and then it goes dim again too.

 

[hang-the-9]

If the backlight is dead it would be quite unfortunate. Is there any way for me to make sure it is the backlight and not something on the circuit boards? I mean I can see all the lights turn on from the back of the tv. Very rarely, the brightness becomes normal and then it goes dim again too.

If you can see the backlight turn on then it is working. Really for the cost of parts that often don't fix things you can just replace it with a working one. Many times people go out and buy power and system boards and issue is the same, or some new issue starts happening.