LG 43LF5900 mainboard failure

[wangcheung]

I have 3 dead 43LF5900's that were taken out during a surge (lightning). All three have the same symptoms where the standby LED is on when plugged in and when the set is turned on the LED blinks three times and then turns off with nothing displayed on the screen.

I tested voltages on the power supply board and all are as listed on the power supply board silkscreen including the EN after switching the set on.

I located one mainboard (EBT63838406)and installed in one set and that took care of the issue. Now my problem is that I can't locate any more boards so I would like to possibly repair the main boards. I have electronics experience but I don't have a service manual for the unit and was wondering if anyone has a service manual for this unit or schematic?

Thanks in advance,

Dan

[freakaftr8]

Re: LG 43LF5900 mainboard failure

EEPROM may have failed. Do you have any voltage on DRV_ON when power is pressed?

[wangcheung]

Re: LG 43LF5900 mainboard failure

I only get PWR_ON (3.3V), no response from DRV_ON when turning on and off the TV. The standby LED works properly when switching from OFF to ON.

EEPROM or flash?

Thanks,

Dan

[freakaftr8]

Re: LG 43LF5900 mainboard failure

Sounds more like eeprom. I believe you can run stand by to DRV_ON and get backlights.

[wangcheung]

Re: LG 43LF5900 mainboard failure

I ordered some EEproms that I think are equivalent. I'll try and replace it on one of the board since I read that a blank will get programmed automagically nothing to lose here

[wangcheung]

Re: LG 43LF5900 mainboard failure

I swapped out the EEPROM without any change in function. Guess I'll keep looking for a point of failure.

Thanks for the suggestion

[RDC55]

Re: LG 43LF5900 mainboard failure

"I'll try and replace it on one of the boards since I read that a blank will get programmed automatically"

And where did you read that? I know it would be possible if the EEPROM's contents were stored in another location such as NVRAM, but it would be nice to have someone confirm how that operation would work and if that is actually true.

[will62]

Re: LG 43LF5900 mainboard failure

Here's a service manual for the 55LF5950. The main boards look the same, possibly just different eeprom data for the panels. It might help you check voltages on the main board, and verify that the esd/tvs protection on your inputs have not shorted to ground.

http://service.minjja.lt/files/?id=2944

[wangcheung]

Re: LG 43LF5900 mainboard failure

Thanks for that Will. I'll check through the service manual now.

[wangcheung]

Re: LG 43LF5900 mainboard failure

Hi RDC55, I was skeptical as well. I read in a post on here somewhere that the EEPROM can be updated if blank from ROM but not if corrupt. I was reaching in the attempt and since I have 3 dead main boards I figured I could sacrifice 1. EEproms are cheap.

I had 3 identical TVs that had the same symptoms, bought 2 main boards that brought 2 to life but can't find a third main board so I'm trying to debug the board now.

thanks

[diif]

Re: LG 43LF5900 mainboard failure

I know there are some Samsung TVs that work this way with the EEPROM being rewritten by the NAND. Not heard of any LGs working this way.
Why not use an external programmer and read from a working EEPROM and write to another before soldering on.

[wangcheung]

Re: LG 43LF5900 mainboard failure

ok, all hopes of repair are lost
I was checking all of the power regulator circuits and found that the 1.2V_MTK output was 0 volts when the POWER_ON was present and then realized that the main IC was getting really hot so it appears the main IC is internally shorted.

Thanks again for the service manual Will, that made all the difference having the schematics available. Come to find out the schematic matched for the 43LF5900

I'll keep my eye out for one more main board. Thanks for the tips and helpful discussion.

[wangcheung]

Re: LG 43LF5900 mainboard failure

something I forgot to mention, while reviewing the schematic for the main board I noticed that ALL surge protection components were labeled OPT which I assume to mean optional because NONE of them were populated on the board. I'm not surprised that all three sets failed at the same time. I'm not sure if this is common practice but I would be hesitant to purchase any LG product seeing that cost cutting has left the main components relatively unprotected to save minimal cost. I guess producing landfill is the latest direction for consumer electronics companies. I was very disappointed to to see that. **end of rant **

[RDC55]

Re: LG 43LF5900 mainboard failure

Really some good information knowing that with a "dead" processor all appears normal except for DRV_ON. It would be interesting to know the logic behind that and why the PWR_ON command even occurs.

Interesting you lost three TV's in one event. Did anything else in the house get wiped out? Were they all connected to cable / satellite boxes or antenna and powered with surge protectors?

"I'm not sure if this is common practice but I would be hesitant to purchase any LG product seeing that cost cutting has left the main components relatively unprotected to save minimal cost."

I would suspect all manufacturers are following the same pattern. It's amazing that one chip now handles all the decoding for HDMI, SCART, LAN, USB, etc. I guess we are happy when we go to purchase a new set, but also bummed that they are increasingly becoming a throw away item.

[wangcheung]

Re: LG 43LF5900 mainboard failure

There is a separate smaller processor that manages the IR functions and power switch and then hands off after the initial power on.

several other devices were lost during the same event, a couple Visio LCD TVs survived though. All were lost through connection to the mains. Surge suppressors weren't able to protect much since this was a lightning strike, although not direct to my house.

it disappoints me that we have become a landfill generation, well not those of us that try and repair equipment, but the norm is to discard.

[freakaftr8]

Re: LG 43LF5900 mainboard failure

Do you have back lights if you jump to DRV on? Remove Drv on pin from mainboard first.

I know I told you to jump this pin but I never got a response to as if you are back lights have come on or not

[wangcheung]

Re: LG 43LF5900 mainboard failure

update - all three sets were returned to working order by replacing the main board (~50$ each).