LG TV Switches On then Off

[RecycleN]

Hi Guys

Wondering if I could get some help - essentially i have an LG TV (Model: LG 47LS5600) that seems to be cycling between on and off. When i put the power cord in, it switches on, has perfect picture and audio for say 5 seconds and then switches off, power light flashes three times. And then cycles through this loop till i pull the power out.

I've tried changing the power cord no difference. I've also opened up the back of the TV and the power board seems perfectly fine - when I say seems fine this is obviously to a novice like me!

Any thoughts on what could be the issue or suggested remedy?

 

[bruceb]

First thing is to check if any electrolytic capacitors are showing signs of bulging on top. If they are they need to be replaced. Second would be to examine the power board very carefully for cold solder joints. If you find any that look iffy, reheat them or resolder them. Also look for any components that show signs of having overheated. If they have, you need to find out which part caused it. Note: You can Google your model and probably find the schematic or service manual, sometimes for free or a small fee.

 

[RecycleN]

Have done a check and couldn't find any blown capacitors or any other type of overheating. (Not sure how i would identify a cold solder)

Here you can find an image of the power board.

I was thinking of simply buying a replacement power board, assume its fully functional which is a risk i know, would that potentially resolve the issue or is it somewhere else?

 

[bruceb]

First your picture of the power board did not get into the post. You need to upload it and then put the image URL into the post using the icon to the right of the Smiley. Second, this link will tell you how to look at and identify bad solder joints. Note: The most common areas for bad solder are on components that have heavy leads, like transformers, potentiometers, big capacitors, big transistors.
This happens because a lot of that is Wave Soldered during assembly and if the parts are not properly cleaned of oxidation. If you find any bad joints, remove the solder, clean the lead and redo,
https://learn.adafruit.com/adafruit-guide-excellent-soldering/common-problems

 

[RecycleN]

Oh cool, that's super informative, i'll check that. Also picture is now in the post!

 

[bruceb]

Once you upload the photo, in most cases as you view it, you can right, click "copy image" and then just Paste it into the post.

 

[sdifox]

The two power transistors near the transformer are the first thing you need to check. The PCB is scorched between them. Unless it is just discoloured heat sink.

 

[RecycleN]

Quick update, purchased a replacement power board, but still the issue persists. So can't be the powerboard