Black screen issue

[patmnr1]

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

[jordan]

If you do something to help

[sparky]

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

[patmnr1]

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.

[sparky]

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

[Turnip]

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.

[sparky]

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

[Turnip]

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.