Anyone with experience repairing a bad MAIN board?

[lotas]

Re: Anyone with experience repairing a bad MAIN board?

You may have a shorted zener diode near the large ZD2311 inductor.

[Diah]

Re: Anyone with experience repairing a bad MAIN board?

3.3V will go to IR section then return to micom... any test with out the IR section in place make no sens

[Davi.p]

Re: Anyone with experience repairing a bad MAIN board?

3.3V will go to IR section then return to micom... any test with out the IR section in place make no sens

you surely need a big pair of eye glasses, that type of design would be by a child..

[Davi.p]

Re: Anyone with experience repairing a bad MAIN board?

for the post 37, yes it seems that the small inductance exploded

[edugimeno]

Re: Anyone with experience repairing a bad MAIN board?

Ok, wait... we may have something.... Lower end of that choke shows continuity from 13V, and upper end of the choke ZERO ohms to ground....
I will look for the above mentiones zenner or any other component behind that pad

[edugimeno]

Re: Anyone with experience repairing a bad MAIN board?

3.3V will go to IR section then return to micom... any test with out the IR section in place make no sens

All my above tests were done with the IR board connected to main board
Thanks

[edugimeno]

Re: Anyone with experience repairing a bad MAIN board?

ZD2311 checks good but Im going to remove caps C2371&C2372 and test them off board

[lotas]

Re: Anyone with experience repairing a bad MAIN board?

Is this zener diode (TVS) short? You can lift one side of it with a soldering iron and check it again or even unsolder it and check if the short is gone.

[edugimeno]

Re: Anyone with experience repairing a bad MAIN board?

TV FIXED!!!! OMG I can't even believe it....
C2371 was shorted. I took it out, checked it offboard, it was 0ohm, tested cap pads on board and no continuity.
Put my pliers end shorting choque and TV turned on, I can't see from the front side as Im holding it all with my hands but Im gona jumper the choke and find an external replacement (what value?) for this cap and from there see what else need attention

GUYS, thanks a million to all those involved in this repair. You were all very helpful!!

[edugimeno]

Re: Anyone with experience repairing a bad MAIN board?

Ok I used an ESR meter and the second parallel capacitor C2372 gives 10uF so that's what Im going to use in place
TNX!

[lotas]

Re: Anyone with experience repairing a bad MAIN board?

Well, that's good, you won't have to buy a new board and save a lot of money.

[edugimeno]

Re: Anyone with experience repairing a bad MAIN board?

Exactly. I have already jumpered the choke and the TV works fine, shows "no signal" etc onscreen, obbey to remote V+, V-, etc...but has the usual LG Blue tint of death. Very intense. As I had already checked this by manually forcing the BL ON some days ago, I had already ordered new strips so they are on their way. Working 43" smart tv for 12€.
Isn't that great?

[Davi.p]

Re: Anyone with experience repairing a bad MAIN board?

This is yet another proof of hundreds that backlight leds dies for external disturbances, not for low quality components or design..

[edugimeno]

Re: Anyone with experience repairing a bad MAIN board?

90% of blueish backlight strips I have repaired were LG Tv's. Some have been Samsung, but not many
This strips use a thin yellow coating above the LED, that originally emits blue light. The combination of the blue and yellow makes the white color. When the yellow film decays, usually due to bad manufacturaing process, in combination with a TV that has the BL set to 100% and is ON for most of the day, ends up with this blue screens.
I don't see any external disturbances other than a bad setting (100% BL)

[jsdffxf]

Re: Anyone with experience repairing a bad MAIN board?

ic3800，The specific workflow of lg I have been exposed to so far should be: mcu sends stb signal,

[TheHexcodeForLibraEmoji]

Re: Anyone with experience repairing a bad MAIN board?

Douse it in IPA and scrub with a boar brush.

[Davi.p]

Re: Anyone with experience repairing a bad MAIN board?

edugimeno so you are telling that the previous owner of tv was happily watch its tv with blue tint and the fault occured to the main board its in a second time and maybe also due to bad components?! Well what a case..

[edugimeno]

Re: Anyone with experience repairing a bad MAIN board?

edugimeno so you are telling that the previous owner of tv was happily watch its tv with blue tint and the fault occured to the main board its in a second time and maybe also due to bad components?! Well what a case..

Absolutely, confirmed. I called him to let him know the TV has 2 issues. 1 was the main board that had to be repaired. 2nd was the LED strips that had turn to blue (as I had forced them to ON). I asked him if he had already realized about this and he said: Yes, I know this TV has been turning to blue along the time

My mother in laws TV is LG and after some years it slowly turned to blue as well with no other issue related to it. I changed the led strips and 2 years later it's all good. And like these, I've repaired maybe 15 more TV with blue tint on Backlight with no other issue linked to it. Like I said most, almost all, were LG

Everytime I see a TV at a public place (hostpitals, bars, etc) that are prone to be a lot of time ON during the day, if they are LG, they already have this blue tint.

Whenever I repair them I always turn the BL down to 50% and warn the user not to go beyond 75% backlight

[Davi.p]

Re: Anyone with experience repairing a bad MAIN board?

so what a crap tv..

[howardc64]

Re: Anyone with experience repairing a bad MAIN board?

I recently replaced blue backlight on 2 < 5 year old LGs. My understanding is the yellow phosphor on top of the blue LED wears out.

LG WebOS TVs have life time on time counter. Both blue backlight TVs were > 10k hours so probably > 5 hr/day. If used for public displays @12hr/day, then will turn blue within 2+ year.

https://www.badcaps.net/forum/showthread.php?t=117199