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Equipment Repairs => LCD TV forum => Topic started by: patmnr1 on April 22, 2014,01:30:46

Title: Black screen issue
Post by: patmnr1 on April 22, 2014,01:30:46

Dear guys, I need some advices , when i switch on my led toshiba(47vl863) , for 30 seconds the image is ok then the screen goes black for one second, then image back to normal, it repeats for 3 to 4 times like that , then gets completely black with sound on, no backlight. I thought it was the inverter, so had it changed but the problem was not solved. My tv was on dynamic mode i.e. baclight at 100%, i noticed that when bringing the backlight to 40% (standard mode) the issue was over. It's quite frustrating to watch on standard mode. Any idea what could be wrong, which board has to be replaced?
Thanks for your help

Title: Re: Black screen issue
Post by: jordan on April 22, 2014,04:21:47

If you do something to help

Title: Re: Black screen issue
Post by: sparky on April 22, 2014,06:19:16

 Hi it sounds like one or tubes faulty can you hear any arcing or smell anything burning when going faulty

Title: Re: Black screen issue
Post by: patmnr1 on April 22, 2014,07:58:55

Thanks for the schematic,
no arcing sound, nor smell when it happens, when I first removed the back panel , noticed that the inverter changed color l(brownish)ike if it was overheatered.
I was also surprised to find that not only the screen was of make Lg but also the power supply and the inverter.
Only the main board was made by Toshiba.

Title: Re: Black screen issue
Post by: sparky on April 22, 2014,10:14:19

Hi try and check connectors to tubes lg have a poor reliability with screens

Title: Re: Black screen issue
Post by: Turnip on April 23, 2014,12:49:27

Hi there,

Seems curious as standard mode functions OK, but as you have a brownish inverter, would resolder drive chips and trannies, as dries might well cause the problem - Chris.

Title: Re: Black screen issue
Post by: sparky on April 24, 2014,09:21:06

Hi if you have changed the inverter board prob tube faulty try and split screen and see if any are discoloured

Title: Re: Black screen issue
Post by: Turnip on April 24, 2014,11:30:58

Hi there,

Could be a thought that the PS is ducking out with full backlight, seems odd that set functions with 40% backlight as surely duff tubes would cause inverter to cut. 

Although recently had a set where the top two inverter trannies had nearly fallen off the panel giving just a black bar at the top, and the inverter didn't cut - Got me confused for a while - Chris.