NotTaR of Television Sets : Loss of Channel after Warmup            
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Loss of Channel after Warmup

If there is a general loss of picture and sound but there is light on the screen, then most likely the tuner or IF stage is pooping out.

With both no sound and no picture but a raster and static, it is most likely a problem in the tuner, power to the tuner, or its controller (if non-knob type).

If it recovers after being off for a while, then you need to try a cold spray in the tuner/controller to identify the component that is failing. Take appropriate safety precautions while working in there!

If it stays broken, then most likely some component in the tuner, its controller, or its power supply as failed. There is a slight chance that it could be a bad solder connection - I have seen these in the tuner modules of RCAs on several occasions (and many other manufacturers - apparently not a solved manufacturing problem even after 40+ years!