LG 43UF7709 - Blinking Screen, No Picture, No Sound

[EUWest]

Hi everbody,

my LG TV 43UF7709 wont turn on. It only tries to show something, but it stays only blinking. So i removed the Backcover and first checked some Voltages.

I get on the powersupply all Voltages correctly, equal to the schematics nearby. The only thing i get maybe wrong is "LED+". On the Powersupply there stand it had to be 50V Output. I only get 38V on LED+. Could this be a failure?

Also there is a LED, LD701 which blinks 6 times in row YELLOW. What can this mean?

I also checked Powersupply out of the chassis. I couldn´t find any issues. But have to say, that i´m not a pro.

I also checked Voltage on TCON Fuse: I get 11,5V on each side.

What i noticed to is that the heatsink on the mainboard run very hot.

Would be have, if we can get this TV back to life

[nomoresonys]

Re: LG 43UF7709 - Blinking Screen, No Picture, No Sound

Test connector from mainboard to powerboard on powerboard side, test with tv plugged in but off then hit power, report both conditions here, give pin number, pin description and condition on and off.

[budm]

Re: LG 43UF7709 - Blinking Screen, No Picture, No Sound

Please provide good clear pictures so we can see what we are dealing with.
You say 'Blinking screen', are you referring to backlights are blinking?

[EUWest]

Re: LG 43UF7709 - Blinking Screen, No Picture, No Sound

So, i will List from Top to Bottom (i think top ist Pin1?)

LEFT ROW, TV PLUGGED BUT OFF
0V "SIN"
0V
0V
0V
0V
0V
0V
0V
0V
0V
3,5V
3,5V
0V
0V "PWR_ON"

RIGHT ROW, TV PLUGGED BUT OFF
0,055V "VSYNC"
0V
0V
0V
0V
0V
0V
0V
0V
0V
3,5V
0V
0V
0V "DRV_ON"

LEFT ROW, TV PLUGGED POWER ON
0,06V "SIN"
0,058V
0V
25V
25V
0V
11,68V
11,68V
11,68V
0V
3,5V
3,5V
0,73V
3,5V "PWR_ON"

RIGHT ROW, TV PLUGGED POWER ON
0,055V "VSYNC"
0V
0V
0V
25V
25V
0V
11,68V
11,68V
0V
3,5V
0V
3,5V
0,08V "DRV_ON"

@nomoresonys i hope you get what i mean, if not i will try to explain it better

@budm i think its the backlight. Blinking Screen is seen in front of the LG TV. If i stand behind, i dont see any white light from holes. It seems like TV try to turn on the screen but sticks in this mode.

EDIT/
I have to say, LD701 is blinking ORANGE not YELLOW^^

[nomoresonys]

Re: LG 43UF7709 - Blinking Screen, No Picture, No Sound

Unplug tv from outlet, unplug cable from powerboard to mainboard, plug tv back in out let, see if backlights come on and stay on.

[EUWest]

Re: LG 43UF7709 - Blinking Screen, No Picture, No Sound

I did unplug connector to mainboard but there are no backlight. Should i stay longer? I testet about 10sec.

[EUWest]

Re: LG 43UF7709 - Blinking Screen, No Picture, No Sound

Any other ideas?

[nomoresonys]

Re: LG 43UF7709 - Blinking Screen, No Picture, No Sound

Maybe try jump starting the powerboard WITHOUT mainboard connected, I think you use a 1k resistor from power on pin to 3.5 standby and another resistor from 3.5 standby pin to drv-on pin, then see if your proper voltages are there and if backlights come on. MAKE sure cable from powerboard to mainboard is unplugged for this test.

[EUWest]

Re: LG 43UF7709 - Blinking Screen, No Picture, No Sound

Yes sir, connected Power on to 3.5 and drv on to 3.5 ans get backlights shining.

On power on and drv on i only get 3.29V. Should be okay i think?
But what does lightning backlight mean? Does the Mainboard have issues?

[nomoresonys]

Re: LG 43UF7709 - Blinking Screen, No Picture, No Sound

Usually that proves the backlights and powerboard are ok, looks like the mainboard is not sending the drv-on signal.

[nomoresonys]

Re: LG 43UF7709 - Blinking Screen, No Picture, No Sound

I would try a replacement mainboard if reasonably priced, I'm not sure why the mainboard doesn't send the signal but it seems to be the problem in many failures.

[EUWest]

Re: LG 43UF7709 - Blinking Screen, No Picture, No Sound

I will look if i can get a replacement Mainboard. Meanwhile i will try to fix my Mainboard, because it cant get more worse then now

Thanks a lot for you guys! Will be Post any Updates in this Theard so maybe other People can profit from the experience

[EUWest]

Re: LG 43UF7709 - Blinking Screen, No Picture, No Sound

I checked some capacitors on the mainboard. Seems like they were shorten. But these are so tiny, i cant read which values they have so i can choose the right replacement capacitor.

Is there anyone, who has an Service Manuell for this TV? I cant finde one

[nomoresonys]

Re: LG 43UF7709 - Blinking Screen, No Picture, No Sound

Looks like drv-on signal from mainboard is too low to turn on the backlights, guess you could try heating the mainboard with a hairdryer a small section at a time including those caps you mentioned and see if there's any change.

[nomoresonys]

Re: LG 43UF7709 - Blinking Screen, No Picture, No Sound

Here's a little test, unplug lvds cable from mainboard to tcon and see if those caps still read short in diode mode, done with tv unplugged and unpowered of course.

[EUWest]

Re: LG 43UF7709 - Blinking Screen, No Picture, No Sound

Looks like drv-on signal from mainboard is too low to turn on the backlights, guess you could try heating the mainboard with a hairdryer a small section at a time including those caps you mentioned and see if there's any change.

These are smd caps, could hairdryer work on this? I thought it only works on elektrolyt caps

[nomoresonys]

Re: LG 43UF7709 - Blinking Screen, No Picture, No Sound

Hairdryer has been known to work on lots of things optos, bga chips, eeproms, different type caps etc etc., do the test in post 15 too.

[budm]

Re: LG 43UF7709 - Blinking Screen, No Picture, No Sound

I checked some capacitors on the mainboard. Seems like they were shorten. But these are so tiny, i cant read which values they have so i can choose the right replacement capacitor.

Is there anyone, who has an Service Manuell for this TV? I cant finde one

When you say shorted caps, what are the resistance readings use Ohm mode?

[nomoresonys]

Re: LG 43UF7709 - Blinking Screen, No Picture, No Sound

Do you see an image on screen with a flashlight when you hit menu or anything?

[EUWest]

Re: LG 43UF7709 - Blinking Screen, No Picture, No Sound

When you say shorted caps, what are the resistance readings use Ohm mode?

Wasn´t at home till today, so i´m sorry for my late response. I will do the suggested Test today.

There are a bunch of shorted caps to the ground (continutiy test not diode mode), if i read the resistance i get 2 different readings:
Some caps are at 2,2 Ohms and some have only 0,3 Ohms.
I´ve done readings with mainboard out on TV on my desk (if its necessary). Now i will try test with flashlight and hairdryer