LG 47LC7DF PSU dead

[farmtech]

Hello, wondering if anyone has a schematic for the LG 47LC7DF power supply board, PN EAY36781301. I replaced the usual bad caps 2 years ago but now the supply is completely dead, the only thing I can find is 5VSB reads about 1.9V. No parts read open or shorted that I can find, was hoping to find a schematic to troubleshoot the standby section of the supply board. Any help would be greatly appreciated.

Thanks,
Nick

[momaka]

Re: LG 47LC7DF PSU dead

Post some pictures of your power supply here. That way we can see what you are seeing.
Also, what brand and series of caps did you use for your replacement caps?

[farmtech]

Re: LG 47LC7DF PSU dead

There is not much to see but I have attached some pics. The PSU is more or less dead, I am just hoping someone can point me to a schematic.

Thanks

[ReeceyBurger123]

Re: LG 47LC7DF PSU dead

Heres a tip you should replace all the smaller capacitors as well they can cause no standby symptoms when they fail.

[farmtech]

Re: LG 47LC7DF PSU dead

I guess I will remove the rest of the electrolytics and see how they test. I will also remove and test the fets. Other than that I will be out of ideas without a schematic.

Are LG PSU schematics really this hard to find? I can't seem to find it anywhere.

[budm]

Re: LG 47LC7DF PSU dead

If you get the spec of the SMPS IC used in the STBY PS, you will see the application notes circuits showing how the IC is used, that is what I do when I do not have the diagram of the board, it does sound like bad startup-running caps.
Is the STBY Voltage low without the main board connected to the power supply board?

[farmtech]

Re: LG 47LC7DF PSU dead

Yes, I get about 1.9 - 2.0V whether it is connected to anything or not. I will try to identify the SMPS IC but I have not been able to trace things very well without the schematic. Thanks.

[budm]

Re: LG 47LC7DF PSU dead

Which one of these matched your board? Look at the barcode sticker.
Up load good clear straight shot of both sides of the board so I can clearly see the parts and the traces on the board.

[budm]

Re: LG 47LC7DF PSU dead

I would replace those small caps in the primary side.

[farmtech]

Re: LG 47LC7DF PSU dead

I will check those out, thanks for the drawing.

[farmtech]

Re: LG 47LC7DF PSU dead

One of those small caps did not read on my capacitance meter but it was not shorted or open either, anyway I replaced it with no luck.

Today I replaced the rest of the small caps even though they tested good or at least close on my meter and sure enough the standby 5V was back. After re-assembly the TV is running again. Thanks for the help Budm.

[budm]

Re: LG 47LC7DF PSU dead

Thanks for the follow-up, more likely they have high ESR.
Did you test the ESR or just capacitance testing?

[stj]

Re: LG 47LC7DF PSU dead

this may be the blindspot of most meters - lack of ripple current handling.

[Don Brotherson]

Re: LG 47LC7DF PSU dead

Well, after reading the posts, it seems unlikely that a schematic exists. That really makes it hard to identify ZD100, which broke in half probably when Q103 shorted. Or it could have been when I was trying to remove it. Either way, I can't identify the value of this ZD. Does anyone out there know this value ? Sure would appreciate it. Thanks !

[budm]

Re: LG 47LC7DF PSU dead

https://www.badcaps.net/forum/showthread.php?t=65334