Need a solution. T.V. is about one year old. We have 3 of the same make. The screen on the newest

Question

T.V. is about one year old. We have 3 of the same make. The screen on the newest T.V. turns 90% black on, so far, 3 Channels. Comcast came out and said it has nothing to do with them since we are getting a signal. need a solution. Will you advise? Thank you. Richard Shepherd, San Ramon, Ca. 94583