Test initiating apparatus for appliances having self-diagnostic testing capability

For an appliance of the type having a control circuit including logic control means for operating the appliance in a power up mode each time power is applied to the appliance followed by selective operation in a self-diagnostic/test mode or a normal operating mode and energized by a pulsating power signal from an external power supply having a fixed nominal frequency, coupled to the appliance by power lines, apparatus for initiating operation in the self-diagnostic/test mode comprising:

• test circuit means adapted for connection in the power lines between the control circuit and the power supply, said test circuit means being selectively switchable between a first state and a second state and operative in its first state to change the frequency of the power signal applied to the control circuit and in its second state to couple the power signal to the control circuit at the power supply frequency;
• means included in the control circuit for generating interrupt pulses marking pulsations of the power signal;
• means included in the logic control means responsive to said interrupt pulses and operative in the power up mode to detect a change in pulse rate relative to that representative of the nominal power supply frequency signifying said test circuit means being in its first state, and to initiate the self-diagnostic test mode upon detection of said change and to initiate the normal operating mode otherwise, whereby operation in the self-diagnostic/test mode is initiated by switching said test circuit means to its first state.

For an appliance having a control circuit including a microprocessor including a read only memory having a control program stored therein, which program includes a power up routine for controlling appliance operation in its power up mode following application of power to the appliance, a self-diagnostic test routine for operating the appliance in a diagnostic/test mode and a normal routine for operating the appliance in its normal operating mode, which control circuit is energized by an alternating current power signal from a power supply coupled to the appliance by power lines, apparatus for initiating operation in the self-diagnostic/test mode comprising:

• test circuit means adapted for connection in the power lines between the appliance and the power supply, said test circuit means being selectively switchable between a first state and a second state and operative in its first state to suppress power signal half-cycles of one polarity and in its second state to couple the power signal unchanged to the appliance control circuit;
• means responsive to said power signal for generating interrupt pulses marking the zero crossings of the power signal;
• the microprocessor including means operative during execution of the power up routine to monitor said interrupt pulses and detect a difference in interrupt pulse rate relative to the nominal power supply frequency, to branch to the self-diagnostic/test routine if such a difference is detected and to branch to the normal operating routine otherwise, whereby operation of the appliance in the diagnostic mode is initiated by switching said test circuit means to its first state prior to applying power to the appliance.