Channel selection apparatus for television receiver

A channel selection apparatus for a television receiver comprising:

• an electronic tuner which is preset to be responsive to a plurality of channel selection tuning potentials for tuning the television receiver to different television channels corresponding to the channel selection tuning potentials;
• selecting means for selecting one of said plurality of channel selection tuning potentials to apply said selected potential to said electronic tuner;
• first circuit means for causing said selecting means to sequentially shift said selected potential through the plurality of channel selection tuning potentials;
• defeat signal output means for producing a defeat signal when said selected potential is shifted;
• a synchronizing signal discrimination circuit for discriminating the presence and the absence of a synchronizing signal of a television signal to produce a discrimination output of a first level when said synchronizing signal is absent and a discrimination output of a second level when said synchronizing signal is present;
• a second circuit means responsive to said defeat signal for producing a pulse output signal of a second level having a predetermined duration when said second circuit means receives said defeat signal, and producing an output signal of a first level at the end of said predetermined duration;
• and
• a first gate circuit having input terminals thereof connected to receive the discrimination output of said synchronizing signal discrimination circuit and said output signals of said second circuit means and having an output terminal thereof connected to said first circuit means,
• said first gate circuit being operative to supply a sequential shift signal of a second level to said first circuit means only when the outputs of said synchronizing signal discrimination circuit and said second circuit means are both at said first level to initiate the channel sequential shift operation, and to supply an output signal of a first level in all other cases to stop the channel sequential shift operation, so that said channel sequential shift operation is repeated so long as the output of said synchronizing signal discrimination circuit is at said first level and said sequential shift operation is stopped when the output of said synchronizing signal discrimination circuit assumes said second level.