LG 32LD550 no backlight stay in stby

[wuffwuff2003]

Hi everybody, I try to describe my Problem with an LG 32LD550.
When turning on the TV, the red Standby Led Begins red flashing. But that's all. No backlight, no Picture. I measured the voltage on the Power PCB . 20V OK / 12V OK / 3,5V OK . Power-On Voltage OK (5V) Only the INVERTER ON/OFF Pin stay at 0V. I checked up the 2 Inverter Transformer (seems OK) also the 4 Power MosFets of the Inverter an of course the fuse. Seems all OK. Does anybody have an idea? or maybe a schematic of this Power Board. His number is: EAX61124201/15.
Many thanks
Best regards

[sordids999]

Re: LG 32LD550 no backlight stay in stby

Posting pictures of the back of your tv showing the boards with clear pictures may help you more with fixing your problem

[wuffwuff2003]

Re: LG 32LD550 no backlight stay in stby

Hello,
Yes of course here are the Pictures:
Best regards

[sordids999]

Re: LG 32LD550 no backlight stay in stby

Thers a repair kit for this PSU board might be worth checking the following capacitors

http://www.ohmsupplies.co.uk/REPAIR-...EV12-LG42LD550

[vinceroger69]

Re: LG 32LD550 no backlight stay in stby

Can you list all the output pins on the PSU by name and what voltage you measure on each of them, both when the TV is in standby and when you press the power button.

maybe read this thread as seems same fault as yours
https://www.badcaps.net/forum/showth...ght=LG+32LD550

[budm]

Re: LG 32LD550 no backlight stay in stby

'Only the INVERTER ON/OFF Pin stay at 0V' Main board is not sending the BL-0N to turn on the backlights.

[wuffwuff2003]

Re: LG 32LD550 no backlight stay in stby

Hi together.
The caps are all checked, I solde them out (all) an checked the capacity an the ESR , all OK.
Here are the voltages first in Standby an second "switched on"

Error: 0 / 1,0
P-Dim: 0 / 1,0
A-Dim: 0 / 3,0
Inv On/Off: 0 / 0
3,5V: 3,5 / 3,5
20V: 0 / 21,4
12V: 0 / 12,6
Power On: 0 / 3,2

Many thanks

[vinceroger69]

Re: LG 32LD550 no backlight stay in stby

As budms post 6 it looks like the mainboard is at fault, as these are hard to find the faults on i usually just swop the board. Just make sure if you do this that all the numbers match inc the ones on white stickers etc.

[budm]

Re: LG 32LD550 no backlight stay in stby

You can disconnect the INV ON/OFF wire going back to the main board first and then use 1K resistor between the INV ON/OFF pin and the 3.5VSTBY pin of the power supply board to force the backlights on to see if you will get backlights and pictures on the screen.

[wuffwuff2003]

Re: LG 32LD550 no backlight stay in stby

Hi,
First I will check if it is the Signal of the Motherboard that is missing, how many voltage can i put on the Inv ON/OFF Pin to check if the backlights will start up?
Thanks

[wuffwuff2003]

Re: LG 32LD550 no backlight stay in stby

Hi sorry Budm I think you were 2 seconds faster than me

[vinceroger69]

Re: LG 32LD550 no backlight stay in stby

ignore you have saw budms post now.

[wuffwuff2003]

Re: LG 32LD550 no backlight stay in stby

Hi,
I traced back the ON/OFF Signal on the Mainboard, because the backlight work when I shorten the ON/Off Pin on the Power Board with the 1k Ohm resistor. On the Mainboard there were 3 resistors, 1 Transistors, all are ok. Then I come to a Microcontroller "UPD78F0513AGB-GAF-AX". On pin 37 P1 is a high Output of 3,2V . This voltage don't Change when I put the TV on or back in Stby. So I think there must be a Major Problem on the Mainboard (microcontrollers or anything else) , so it's poor but I must Change the Mainboard. Thanks for your help!

[budm]

Re: LG 32LD550 no backlight stay in stby

So you are able to force on the backlights as I suggested by disconnecting the ON/OFF wire first, do you see the pictures on the screen? If not then you have more than just BAD on/off signal problem.

[wuffwuff2003]

Re: LG 32LD550 no backlight stay in stby

Hi, no he stack in standby or in boot up process. I don't think that there is a possibility to update the Firmware or is it? I've nothing find on the Internet
Many thanks

[wuffwuff2003]

Re: LG 32LD550 no backlight stay in stby

Here's the schematic

[wuffwuff2003]

Re: LG 32LD550 no backlight stay in stby

Hi again, I have posted the schematics. I trace back to the IC1002 in the schematic. When I pull down PIN10 on the IC the backlight starts, so the Signal of the IC won't come down to the GND Level, so it's a Problem with the Startup process itselfs, this is causing the LED flashing all the time. Maybe you can help me when I give you the state of the Pin's of the IC1002:
Pin 1,2,3,4,6,8,10,11,12,13,15,16,17,18,19,20,21,22,23,25,26,29,36,39,40,48 = 3,5V
Pin 5,7,9,14,24,27,28,30,31,33,34,35,38,42,43,44,45,47 = GND
Pin 32,46 = 2,6V
Pin 37 = 1,2V
Pin 41 = 3,6V alternate 32,768 MHz

Maybe you find a bug of an Input of the IC?
Many thanks

Andy