Sharp R930AK Service Manual - Page 13

R-930AK R-930AW DESCRIPTION AND FUNCTION OF COMPONENTS DOOR SENSING AND SECONDARY INTERLOCK SWITCHES The door sensing switch in the primary interlock system is mounted in the upper position on the latch hook, the secondary interlock switch is mounted in the lower position on the latch hook. They are activated by the latch heads on the door. When the door is opened, the switches interrupt the circuit to all components. A cook cycle cannot take place until the door is firmly closed thereby activating both interlock switches. The primary interlock system consists of the door sensing switch and primary interlock relay located on the control circuit board. DOOR SENSING SWITCH MONITOR FUSE MONITOR SWITCH SECONDARY INTERLOCK SWITCH OUTER CASE SWITCHES The two outer case switches are mounted near the power supply cord at the oven cavity rear plate. When the outer case cabinet is installed with the screws, one of the screws pushes the actuator and then the actuator pushes each plungers of the two outer case switches and their contacts are closed. When a cabinet mounting screw which is pushing the actuator is removed, the two outer case switches interrupt the circuit to the all components. WARNING The circuit to all components can be connected to the power supply without the outer case cabinet by reinstalling the cabinet mounting screw. BUT AT THAT TIME, NEVER TOUCH ANY PARTS OF THE HIGH VOLTAGE CIRCUIT TO AVOID ELECTROCUTION. This outer case mounting screw is pushing the actuator. Figure D-1. Door sensing switch, monitor switch and secondary interlock switches ACTUATOR OUTER CASE CABINET MONITOR SWITCH The monitor switch is mounted on the middle position of latch hook. It is activated (the contacts opened) by the lower latch head while the door is closed. The switch is intended to render the oven inoperative by means of blowing the monitor fuse when the contacts of the primary interlock relay and secondary interlock switch fail to open when the door is opened. Functions: 1. When the door is opened, the monitor switch contact close (to the ON condition) due to their being normally closed. At this time the door sensing and secondary interlock switches are in the OFF condition (contacts open) due to their being normally open contact switches. 2. As the door goes to a closed position, the monitor switch contacts are first opened and then the door sensing switch and the secondary interlock switch contacts close. (On opening the door, each of these switches operate inversely.) 3. If the door is opened, and the primary interlock relay and secondary interlock switch contacts fail to open, the monitor fuse blows simultaneously with closing of the monitor switch contacts. CAUTION: BEFORE REPLACING A BLOWN MONITOR FUSE TEST THE DOOR SENSING SWITCH, PRIMARY INTERLOCK RELAY, SECONDARY INTERLOCK SWITCH AND MONITOR SWITCH FOR PROPER OPERATION. (REFER TO CHAPTER "TEST PROCEDURE"). NOTE: MONITOR FUSE AND MONITOR SWITCH ARE REPLACED AS AN ASSEMBLY. OUTER CASE SWITCHES THERMISTOR The thermistor is a negative temperature coefficient type. The temperature in the oven cavity is detected through the resistance of the thermistor, and then the control unit causes the heater relay to operate, thus the current to the heating element is turned ON/OFF. MAGNETRON TEMPERATURE FUSE. The temperature fuse located on the waveguide is designed to prevent damage to the magnetron if an over heated condition develops in the megnetron due to cooling fan failure, obstructed air guide, dirty or blocked air intake, etc. Under normal operation, the temperature fuse remains closed. However, when abnormally high temperatures are reached within the magnetron, the temperature fuse will open at 302˚F(150˚C) causing the oven to shut down. CONV. THERMAL CUT-OUT The thermal cut-out located on the left side of the thermal protection plate (left) is designed to prevent damage to the heater unit if an over heated condition develops in the heating unit due to convection fan failure, thermistor failure, obstructed air ducts, dirty or blocked air intake, etc. Under normal operation, the thermal cut-out remains closed. However, when abnormally high temperatures are reached within the heater unit, the thermal cut-out will open at 302˚F(150˚C) causing the oven to shut down. When the thermal cut-out has cooled, the thermal cut-out closes at 266˚F(130˚C). 11