Abstract: A television receiver includes a standby power supply, and an operational or run mode power supply. A microprocessor coupled to the standby power supply controls switching between a run mode, where the standby and run mode power supplies are operative, and a standby mode where only the standby supply is operative. The switching is normally made in response to switch inputs or in response to a signal from a remote controller. The microprocessor is in digital communication with a digital circuit, such as a phase locking tuner, over a bidirectional data bus. The microprocessor is programmed to poll the digital circuit periodically and to monitor the data on the data bus for an expected response to a poll. When the digital circuit fails to respond to the poll, or responds inappropriately, as may occur with lack of adequate power to the digital circuit from the run power supply, the microprocessor automatically switches into the standby mode and disables the run supply.