LG 55la965w Black screen no 3.3v INV ON signal

[tiprat63]

Hi , i would really like some help to diagnose and repair this TV.

I'm not an expert but have knowledge of electronics, i actually work on high pressure cleaning equipment. I have various pieces of test equipment, but no oscilloscope.

I'll try and keep it short as to what happens and what i have tested.

Tv was working fine , then just went off.
plug it in and the red standby led is on solid.
turn on TV, the red led blinks 3 times then goes out.
No picture or logo comes on the screen.
Turn the Tv off and back to solid red Led.

Checked voltages when tv turned on.

All voltages as stated on power board apart from the INV ON 3.3v. When measuring the P dim there was no voltage but the meter fluctuated whilst turning on and off , but still no reading .

I have read about the 'wake and bake' repair in the oven but would actually like to know why the 3.3v is not coming from main board .

According to the flow chart in the service manual it requires a new main board.

Some of the heatsinks over the chips on the mainboard are warm, also on the ultra Hd board.

There is a lot of what looks like silicon oil on the heatsinks, which has also migrated onto the boards, can this cause problems?

Any help would be appreciated on this ,

Many thanks ,
Andy

[neilc6]

Re: LG 55la965w Black screen no 3.3v INV ON signal

LA and LN series suffer from backlight failures. The TV is on but the backlight has shut off. https://techhometravel.com/lg-ln-ser...ed-backlights/

[tiprat63]

Re: LG 55la965w Black screen no 3.3v INV ON signal

Hi and thanks for that info.

There is no LOGO flashing on turn on .
24v to inverter but no BL ON signal

Any ideas?

[tiprat63]

Re: LG 55la965w Black screen no 3.3v INV ON signal

i like information to diagnose problems my self, hard facts, not hearsay. I will check all voltages again tomorrow and list the points they were taken on the board/s .

Hope fully some one will be able to assist.

Thanks.

[R_J]

Re: LG 55la965w Black screen no 3.3v INV ON signal

Post some pictures of the back of the tv showing the boards, When I look up this model it is an LED backlight tv so what inverter are you talking about? usually the inverter is for ccfl's. This tv should have a EAY63069001 power supply that drives a seperate led driver board. It is likely you have an open led string in the panel

[tiprat63]

Re: LG 55la965w Black screen no 3.3v BL ON signal

Thanks for the reply , i shall post pictures you requested later on.

With the power readings .

Sorry about saying inverter board, i've been reading so many manuals of different TVs . I should say LED power board, This is seperate to the main power board,

[tiprat63]

Re: LG 55la965w Black screen no 3.3v INV ON signal

Hi , here should be a picture of the back of the TV

I don't have the power readings / voltage readings from the power supplt to main board at hand.

I tested the led strips with an led tester and they were both around 230v.

The DRV on 3.3v was missing and no pdim or Adim as mentioned.

I depinned the DRV on and both DIM wires , as i read a similar problem on this forum that was very informative. I did order some 1k resistors to do the test mentioned in the post .
I thought a 3v battery would suffice seeing as the wires were depinned.

I powered the DRV on wire with the battery and the backlights came on but just a white snowy screen .

There is a small ribbon cable from LED driver board to Tcon board . I disconnected this and still the same on the screen.

Now i beleive i have to test the 12v power to TCON board, there is a supplementary power connector according to the Tcon training manual i read .Will this be all i need to test?

Many thanks for any help given , i have got this far by reading other posts and i am gaining a much better understanding of it all .

[tiprat63]

Re: LG 55la965w Black screen no 3.3v INV ON signal


Hi , here should be a picture of the back of the TV

I don't have the power readings / voltage readings from the power supplt to main board at hand.

I tested the led strips with an led tester and they were both around 230v.

The DRV on 3.3v was missing and no pdim or Adim as mentioned.

I depinned the DRV on and both DIM wires , as i read a similar problem on this forum that was very informative, I think it was budm that was assisting someone. I did order some 1k resistors to do the test mentioned in the post .
I thought a 3v battery would suffice seeing as the wires were depinned.

I powered the DRV on wire with the battery and the backlights came on but just a white snowy screen .

There is a small ribbon cable from LED driver board to Tcon board . I disconnected this and still the same on the screen.

Now i beleive i have to test the 12v power to TCON board, there is a supplementary power connector according to the Tcon training manual i read .Will this be all i need to test?

Many thanks for any help given , i have got this far by reading other posts and i am gaining a much better understanding of it all .

[budm]

Re: LG 55la965w Black screen no 3.3v INV ON signal

Can you please re-take straight shot pictures of the back side of the TV?
It is hard to see how all the boards are connected together in your picture.

[tiprat63]

Re: LG 55la965w Black screen no 3.3v INV ON signal

Sorry just realised hat pic was upside down too.

here are more , but at the mo i have very low light levels so had to use a flashlight to take pics.

I will take better ones tomorrow if needed .

many thanks

[budm]

Re: LG 55la965w Black screen no 3.3v INV ON signal

I will wait for better and focused pictures.
There are so many cables between boards but the pictures are too poor to see how they all connected together.

[neilc6]

Re: LG 55la965w Black screen no 3.3v INV ON signal

If DRV_ON is not going high to turn on the backlights then the main board is suspect since the signal comes directly from the main processor. You can try baking the board but it usually doesn't last. Heating the processor with a hair dryer could expand the joints enough to make contact and turn on the TV to confirm the failure.

[tiprat63]

Re: LG 55la965w Black screen no 3.3v INV ON signal

I checked the T con voltage when TV turned on, No 12v on supplementary power connector at the fuse.

I checked the power at the ultra hd board, which comes from power supply board. 12v, but no 12v coming from HD board to T con.

sounds like the main board is gone from reading .

What do you think , main board or the ultra hd board, or both ?

[tiprat63]

Re: LG 55la965w Black screen no 3.3v INV ON signal

Hi folks ,
Just an update to let you know how i went on with this problem.

The mainboard went in the oven after applying no clean flux .
380 degrees monitered carefully with oven thermometer, had to keep fiddling with oven thermostat, increased temperature to 410 over the space of 10 mins.
I could see through the the glass door that the solder looked shiny like a fresh solder joint.
turned off the oven, opened the door and let it cool down.

replaced board in TV and lo and behold it fired straight up, LG logo , then NO SIGNAL as i hadn't got anything connected to it.

Thanks for all help.

[dick_barton]

Re: LG 55la965w Black screen no 3.3v INV ON signal

As neilc6 said this tends to be a short term fix but hopefully long enough to source a replacement mainboard.

[nomoresonys]

Re: LG 55la965w Black screen no 3.3v INV ON signal

Now use a fan or 2 to try to keep things from overheating, put simply...heat kills.