LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

[Seb932]

Hi,

i'would like to fix my not working LG 49UB850V tv.

Symptoms:
-AC plugged in, Standby LED not working
-Switching on, Standby LED blinks 3x. LD2300 on mainbord lights up and after ~30s LD701 on PWS board starts to blink 5x repetetive

Checked already:
-Powersupply Output in Standby => 3.5V ok
-Switching On => PWR_On on P201 goes high and 3.5/12/24V are present on P201

Any suggestions what to check next?

Thanks in advance!

[nomoresonys]

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

Good focused straight on pictures of each board and one of the whole back as to see how everything is connected.

[Seb932]

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

Good focused straight on pictures of each board and one of the whole back as to see how everything is connected.

I've attached the requested pictures, hopefully sharpness & resolution is ok, otheriwse i need to use better camera.

[nomoresonys]

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

Easy things first, check over the solder joints on powerboard, reflow any that look suspicious, check all the resistors and diodes on top of the board, youtube is your friend for how to videos if needed, examples of bad solder joints there: https://www.google.com/search?client...h=599&dpr=1.09

[Seb932]

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

Easy things first, check over the solder joints on powerboard, reflow any that look suspicious, check all the resistors and diodes on top of the board, youtube is your friend for how to videos if needed, examples of bad solder joints there: https://www.google.com/search?client...h=599&dpr=1.09

Thanks for recommendation, will try to check and resolder suspicious joinst.

[Seb932]

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

Have checked solderpoints, found some suspicious pins and resolderd it. Also have done some additional measurements.
Started with IC3000, responsible for "power on" sequence

If TV is switched on, the IC3000 enables the different voltage regulators. I've measured input signals (from IC3000) and output:
POWER_ON/OFF1 => IC2304 5V => +5V_NORMAL OK
POWER_ON/OFF2_1 => IC2301 3.3V => +3.3V_NORMAL OK
POWER_ON/OFF2_2 => IC2302 2.5V => +2.5V_Normal OK
POWER_ON/OFF2_3 => IC2303 1.5V => NOK PWM/rectangle signal with ~650kHz and 12V Peak
POWER_ON/OFF2_3 => IC2300 1.0V => NOK PWM/rectangle signal with ~340kHz and 12V Peak
POWER_ON/OFF2_4 => IC3409 1.2V => NOK PWM/rectangle signal with ~500kHz and 12V Peak

Any further ideas?

[Diah]

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

you have much fault at LED BL

[Seb932]

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

you have much fault at LED BL

BL is fully functional. Tested by maual bridging SBY 3.5V to POWER_ON and DRV_ON on SMPS w/o connection to Mainboard.

[nomoresonys]

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

Test drv_on pin at connector on powerboard, with everything hooked up, does the voltage change when you power up tv.

[Diah]

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

BL is fully functional. Tested by maual bridging SBY 3.5V to POWER_ON and DRV_ON on SMPS w/o connection to Mainboard.

what does DRV_ON to do with BL ????????? this is new to me

sow us the print chart on the PSU of the socket which go to MB

[nomoresonys]

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

Nah, it's the same old shit, mainboard sends drv_on signal to powerboard, powerboard turns on backlights, no signal no backlight.

[Diah]

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

DRV_ON to switch 12V T-CON Matt

[Seb932]

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

what does DRV_ON to do with BL ????????? this is new to me

sow us the print chart on the PSU of the socket which go to MB

Sorry, this was a typo. DVR_ON is correct. Pin2 on P201 PSU side. Its normally feeded from INV_CTL (IC3000). Will enable Backlight.
If i bride SBY 3.5V on PSU with POWER_ON Pin1 P201 => all voltages are anabled on PSU. If 3.5V are supplied to DVR_ON on PSU side the backlight lights up.

[Diah]

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

Nah, it's the same old shit, mainboard sends drv_on signal to powerboard, powerboard turns on backlights, no signal no backlight.

in general TV PSU design.. how many STB (3.5V) pins you have at the sockets = how much signal the MB send to PSU during start .... i think here in this LG he had 3 pins STB means = 3 signal

[nomoresonys]

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

Do test in post #9, I think we want to see if the mainboard is sending drv_on signal, we know it works when jumped stand alone from your test.

[Diah]

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

Sorry, this was a typo. DVR_ON is correct. Pin2 on P201 PSU side. Its normally feeded from INV_CTL (IC3000). Will enable Backlight.
If i bride SBY 3.5V on PSU with POWER_ON Pin1 P201 => all voltages are anabled on PSU. If 3.5V are supplied to DVR_ON on PSU side the backlight lights up.

then if you said so 12V & 24V you have and BL good,,, then why you work on PSU...
disconnect the panel from T-CON and try turn on normal.. BL should turn on and the Audio optic out put should lit red too if yours statement before correct

[Seb932]

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

Do test in post #9, I think we want to see if the mainboard is sending drv_on signal, we know it works when jumped stand alone from your test.

No it does not come, checket on PSU side and on IC3000 as well. Pin stays Low...

[Seb932]

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

then if you said so 12V & 24V you have and BL good,,, then why you work on PSU...
disconnect the panel from T-CON and try turn on normal.. BL should turn on and the Audio optic out put should lit red too if yours statement before correct

Have tried it. T-Con disconnected from PSU & Mainboard but nothing changed => Switching on, Standby LED blinks 3x. LD2300 on mainbord lights up and after ~30s LD701 on PWS board starts to blink 5x repetetive. No Backlight and also no red light in optic port. Additional a quietly buzzing noise in the region of IC100 occurs...
Put T-CON in again, buzzing sound is still there...

[Diah]

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

by the way,,, you can also move load on MB, by disconnecting speaker and wifi /BT module from it then turn on,,, this is weakness by LG

[Seb932]

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

Have tried it. T-Con disconnected from PSU & Mainboard but nothing changed => Switching on, Standby LED blinks 3x. LD2300 on mainbord lights up and after ~30s LD701 on PWS board starts to blink 5x repetetive. No Backlight and also no red light in optic port. Additional a quietly buzzing noise in the region of IC100 occurs...
Put T-CON in again, buzzing sound is still there...

Maybe I've missunderstood. I've disconnected T-CON from the Mainboard. But reading carefully, you mean disconnect the panel from T-CON ...
Tried again.... same result as before. Also in combination with disconnected speakers & wifi module...