No audio no video no backlight on LG47LX9900

[Ashish_Jamesh]

Re: No audio no video no backlight on LG47LX9900

Connector P-201

NC=0.1V (its value increased to 0.2V, 0.3v after few minutes)
PDM=2.7V
DRV ON=00
Power On=3.3V

Connector P-205

PDM=2.7V


Connector P-204

NC=0.1V (its value increased to 0.2V, 0.3v after few minutes)
PDM=2.7V

[budm]

Re: No audio no video no backlight on LG47LX9900

PDM=2.7V PWM Dimming control signal is present, it comes from the main board.
DRV ON=00 BL-ON (Backlights ON) signal is not present, it comes from the main board. I do not know if this signal is locked out due to error some where or just bad main board.

[vinceroger69]

Re: No audio no video no backlight on LG47LX9900

its possible i guess as well if this is a common issue that your replacement mainboard is faulty too.

[Ashish_Jamesh]

Re: No audio no video no backlight on LG47LX9900

PDM=2.7V PWM Dimming control signal is present, it comes from the main board.
DRV ON=00 BL-ON (Backlights ON) signal is not present, it comes from the main board. I do not know if this signal is locked out due to error some where or just bad main board.

DRV ON=00 BL-ON (Backlights ON) signal is not present may be because of bad main av board. So as per ur opinion PWM and DRV ON signals coming from mainboard to power supply board? Or it is come from PSU to mainboard? My led tv has separate MASTER LED DRIVER Board and SLAVE LED DRIVER Board. So is there any way to repair the board? I checked the board very carefully there is no any burnt/shorted component inside. And as mentioned previously my set turned on and give backlight along with half screen black (with backlight) and half screen with vertical strips(with backlight). But dont know why it was not give backlight again. Is it possible to reset mainboard or something like that? I have spare mainboard so I have parts of its if it required any.

[Ashish_Jamesh]

Re: No audio no video no backlight on LG47LX9900

I search online and got something like this, is it possible?

http://www.justanswer.com/tv-repair/...wer-white.html

1] Ok, yours is integrated which means your power supply board isn't lighting up the LED backlights

2] There is a separate command line on the plug from the main board to the power board. While LG did not number the pins, nor tell you if the TOP pins are Odd or Even, They did give you a layout of the pins and their positioning in relation to each other.

Power on switch is likely that BLUE wire, under it is likely your first 20 volt line.

Since the DRV ON wire is the 4th one from the bottom, and so is 12 Volts....it's easy to KNOW the 12 Volts is on the same side (top or bottom) as the Power on pin. And you know the DRV ON command line is going to be a 3.5 Volt or 0 volt command.

So check it when you press the power button. Does it switch from 0 to 3.5Volts like the Power On line does?

Remember -- the Power on just turns on the power supply board, and the DRV On powers up the LED board stacked on top of the Power board.

You have to switch BOTH on before your LEDs Light up.

You want to know a little trick I do?


If you unplug the control cable from the main board, you can use the 3.5 volt standby supply on the plug to jumper 3.5 volts over to the Power on and DRV On pins.


I stick a resistor or capacitor leg into the holes and jumper both command lines to the 3.5 volts....then see if the LEDs Light up or not.

[Ashish_Jamesh]

Re: No audio no video no backlight on LG47LX9900

I searched online and got following:

https://electro-medical.blogspot.in/...y-and-led.html

[Ashish_Jamesh]

Re: No audio no video no backlight on LG47LX9900

Psu checked with above mentioned trick, backlight works perfectly. So my psu is ok there may be some issue in main avboard. I have its circuit diagram but i cant understand how to enable drv_on/inverter on signal from this....

[Ashish_Jamesh]

Re: No audio no video no backlight on LG47LX9900

PDM=2.7V PWM Dimming control signal is present, it comes from the main board.
DRV ON=00 BL-ON (Backlights ON) signal is not present, it comes from the main board. I do not know if this signal is locked out due to error some where or just bad main board.

BUDM is there any suggestion to turn on backlight signal on?

[Ashish_Jamesh]

Re: No audio no video no backlight on LG47LX9900

I able to repair mainboard with the help of its schematic diagram. But facing one problem. If pcb of mainboard touch the metal part of led tv panel back light suddenly goes off but if I put it on paper or any non metal material then the tv works perfectly. Anyone have any idea? How can I solve this.

[Ashish_Jamesh]

Re: No audio no video no backlight on LG47LX9900

PDM=2.7V PWM Dimming control signal is present, it comes from the main board.
DRV ON=00 BL-ON (Backlights ON) signal is not present, it comes from the main board. I do not know if this signal is locked out due to error some where or just bad main board.

BUDM Finally I repaired my LG LED tv but there is still some issue with it. Like following:

1. When I turn on LED TV it turn on and tv start normally with audio and video but suddenly display went away and only backlight on and some king of short circuit sound coming from the TV and it restart automatically. Same processor continue for few days and sudden it works as good as new led without any issue.

2. I notice that If I wall mount the led it having above mentioned issue but after having this issue I removed it from wall mount and open the back cover of led and reconnect it then It works perfectly.

3. When TV works fine and I play movie from USB Drive and when I change the movie screen went dark for few seconds.

you can see this issue on this video
https://www.youtube.com/watch?v=tN-dGJDsRiE

[vinceroger69]

Re: No audio no video no backlight on LG47LX9900

Maybe see if theres a firmware update available also when you was playing your film i noticed one or two lines running top to bottom of the lcd have these always been there.

[Ashish_Jamesh]

Re: No audio no video no backlight on LG47LX9900

Maybe see if theres a firmware update available also when you was playing your film i nortice one or two lines running top to bottom of the lcd have these always been there.

Prior there was only a single black line shows on display but after issue on Main
board and T-con I replace both board and noticed 1 green (green-yellow color) color changing line and 1 solid line (very dim to see from distance) on display. I already update its firmware with latest available on LG website.

I m really confused because If I open the tv reconnect mainboard and all its cable connector and put the back cover again then tv works perfectly with only issue of blank screen while changing movies on USB Drive, otherwise all works perfectly. But when I wall mount it, it start normally then display gone (back light on) then creats loud short circuit chirping sound and frozen the display and restart. I did all these exercise from more then 100 times but same result.

[vinceroger69]

Re: No audio no video no backlight on LG47LX9900

maybe try putting the tv back together but dont wall mount it lie it flat on a surface but so you can see the screen still does the tv still go wrong in this position? as maybe when wall mounted the weight is pulling down on all the parts so when it gets warm etc maybe breaking a bad joint hence trying it laid flat and see if still plays up.

[Ashish_Jamesh]

Re: No audio no video no backlight on LG47LX9900

maybe try putting the tv back together but dont wall mount it lie it flat on a surface but so you can see the screen still does the tv still go wrong in this position? as maybe when wall mounted the weight is pulling down on all the parts so when it gets warm etc maybe breaking a bad joint hence trying it laid flat and see if still plays up.

Yup you are right I tried it but tv works mostly perfectly on flat surface but sometimes it cause problem as i mentioned earlier. You can see that issue on my youtube video.

[vinceroger69]

Re: No audio no video no backlight on LG47LX9900

the other thing worth trying is see if its heat related take the back of the tv and aim a cold air fan at the mainboard does the tv still play up?

[Ashish_Jamesh]

Re: No audio no video no backlight on LG47LX9900

the other thing worth trying is see if its heat related take the back of the tv and aim a cold air fan at the mainboard does the tv still play up?

Yesterday I reopen LED for checking the fault. I noticed 1 thing, If I tighten the screw of Main AV Board it stop to work (no backlight no audio nothing just TV turn on and off and respond on remote). If I loose the screw then its works normally but after put the cover back and if cover touch the main AV board it again freeze with backlight give noise and restart. after restart some time display come and some time not. 2 thing I noticed that If i turn off LED then its power indication LED stayed on for more than 3-4 minutes Its strange because It should hardly last long for few seconds not for few minutes. So whats ur suggestion?

[Ashish_Jamesh]

Re: No audio no video no backlight on LG47LX9900

the other thing worth trying is see if its heat related take the back of the tv and aim a cold air fan at the mainboard does the tv still play up?

Sir Can you help me to repair my led?