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Equipment Repairs => LCD TV forum => Topic started by: bonesy on April 26, 2017,08:16:43

Title: LG 42LV550T no sound or picture.
Post by: bonesy on April 26, 2017,08:16:43

This one when plugged in comes on red st-by light,press power button r/s you get a white light,flashes two or three times then solid white.At no time do you see even a flash of back lights on screen.I've pressed menu button & shone torch at screen,but no sign of back lights at all.The multi connector that goes off to the SSB,all voltages as marked,but one marked drive on,which I guess is for the LED back lights,doesn't seem to move at all.Back light control is very complicated,with a bank of transistors & a micro i.c. on the back of the board,I've tried to see if any drive voltage comes up,but no sign.No signs of stress on components in power supply or ssb boards.

Title: Re: LG 42LV550T no sound or picture.
Post by: downunder on April 27, 2017,03:19:38

Hi bonesy,

Definitely a main board problem. Have you tried to reflow the micro, or bake the main board in an oven?            Bruce

Title: Re: LG 42LV550T no sound or picture.
Post by: bonesy on April 27, 2017,09:31:37

I think it most likely is,as I say the drive into the power board is missing,Can't see an error voltage from power to ssb,all other power rails are running.I've never Cooked a signal board before,whats the best method & how successful is it?Would it spoil a roast chicken dinner if I did them together LOL?

Title: Re: LG 42LV550T no sound or picture.
Post by: Turnip on April 27, 2017,12:25:29

Hi Bonesy,

Bruce is the king of board baking. Tried it once myself in a new fan oven where I assumed the temperature was accurate. Oven got to 180C so turned it off and gave the board 10 minutes.

Wife noticed Black things with legs at the bottom, and the SSB didn't quite go afterwards.

Would suggest using a clip on thermometer on the shelf used - Chris.

Title: Re: LG 42LV550T no sound or picture.
Post by: downunder on April 28, 2017,08:01:20

Nothing wrong with wife's eyesight then, Chris.

Hi bonesy, preheat oven, 180*. PCB on a tray, component side up. 10 minutes, then open door and let it cool naturally in the oven.

Success rate is quite high, although I've had a few returns. Sometimes smelly so put the chook in later.                Bruce

Title: Re: LG 42LV550T no sound or picture.
Post by: Turnip on April 28, 2017,10:18:04

Hi Bruce,

Suspect ovens down under are more accurate than ones used the right way up.

Could be that the oven thermometer has a bit of a lag, but will maybe get to it after a while, which isn't much of a problem with the Chook, being 90% water, so it dries out a bit before combustion.

Clip on devices are a couple of Squid from China, and even the wife finds 'em useful for touchy stuff incorporating little water - Chris.

Title: Re: LG 42LV550T no sound or picture.
Post by: bonesy on April 28, 2017,10:35:34

Thanks Bruce,I'll wait & see what customer wants to do.There were a couple of screws missing from back cover,which made me suspicious about the set having been somewhere else first.