This is no more than the tuner has lost sensitivity or if this television is Cable TV, the signal to noise ratio are very close together.
In most modern televisions The AGC voltage at the tuner will be about 8 volts with a weak signal caused insufficient micro volts R.F. energy getting into the front end of the tuner. On the other hand if Noise floor os too high and so is the desirable signal the ACG voltage will be low, 2 ~ 3 volts.
It is always best to substitute the signal input to the TV with another known good signal, or try the video input the TV in question, if it has one. These tests will serve as a method to prove what is working.