First, check whether the signal output source of the TV is consistent with the signal source required by the set-top box, aim the TV remote controller at the TV, press the "signal source" button, select and input the signal source matched with the set-top box, and generally you can resume normal viewing. In addition, if the cable connection between the TV and the set-top box is not correct, the screen will appear and cannot be viewed normally. Reconnect the hole to a valid cable and see if the signal can be restored. Generally, the stable output voltage of TV is 5V, 3.3V, 2.6V,1.2v. If voltage instability is detected, a screen will appear. Finally, check the hardware of the TV, such as whether the signal input interface is not well connected with the circuit of the motherboard, whether the CPU of the TV can't recognize the input signal, or whether other parts of the motherboard can't recognize the signal input command normally. The identification of these problems requires professional instrument knowledge and maintenance knowledge, so it is necessary to contact professional maintenance personnel for voltage test or comprehensive and detailed inspection and maintenance of TV sets.