TV Black-out. My TV screen goes blank but the sound stays on. The screen is on at first but

Question

My TV screen goes blank but the sound stays on. The screen is on at first but reduces to a white center dot and goes black but the sound stays on. When it is turned off and put back on, the screen comes back to life. This may happen a few times and then it stays on for the rest of the evening. The frequency of the blackout has increased from once in a while to a few times a viewing. Sometimes it is okay. A tap on the side seems to work sometimes. What is the problem and is it fixable and worth it? Can I get a part and replace it myself? It's been a great TV. ThanksFranko