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What is the model number of your TV?
The model number you provided is not a valid sony model. But I would say that your TV is an LCD projection TV. The turning off and on indicates a bad lamp. You would need to replace the lamp.
I hope this answers your question and if you have more please feel free to ask.
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Neils answer is most likely correct. Your model is a KDFE50A10, and the bulb can easily replaced by you.
This is a known failure mode for lamps. They will stay on for anywhere from a few seconds to several minutes, shut off, then the TV re-fires the lamp, then it will repeat the cycle.
You can order a new lamp by clicking Sony XL2400 Lamp. If you have your owners manual, the procedure to replace the lamp is on page 86, but if you don't have that, I can describe how to do it. It's reaaly a snap.
Hope that helps, let me know if there's anything else I can do for you, and thanks for using JustAnswer!
Sure. Very easy.
On the right side (facing the set) towards the back is an access panel that just snaps off when you push the tab down. Then you'll see a gray plastic bar. Turn that bar counterclockwise, and that panel will open. Then you'll see the lamp assembly. Just lift up on the black ring and pull it out. Take the new lamp and put it in just like the old one cam out. Replace the panel with the plastic bar, snap the access panel back on, and you're done!