The tv turns off by its self

A bad inverter board will produce this exact symptom. They are commonly available on EBay for about $60 USD The part number is. 1FSA10164 It should take about 20 minutes to replace without great difficulty.

If you or someone you know is good at component level PC Board repair this issue is almost always a bad transformer. All it takes is for one of the 6 transformers to have and open winding and the TV will start breifly and then shut down because it has a comparator circuit that monitors all 6 outputs to the lamps. If one of the outputs is missing the TV goes into "Protection Mode" and shuts itself down. The individual transformers can be checked by using a digital multimeter and checking resistance of the windings, should be about 2.7 MOhm, if one reads Zero Ohms, replace it. (You can check the resisitance while they are soldered to the board. Power down the set and let it sit for a bit them remove the connectors and the 6 mounting screws to pull the card.) The transformers are available for $4.95 from Electronica-usa.com the part number is LTZ2PCOMS008 (and yes the shipping costs more than the part, but still cheaper than tossing the TV)

Sleep is on timer