SHARP R-24STM
Service Manual

OPERATION SEQUENCE
MICROWAVE OFF CONDITION
Closing the door activates the door interlock switch (monitored latch switch). IMPORTANT When the oven door is closed, the monitor switch contacts COM - NC must be open. When the microwave oven is pluged in a wall outlet (230240V 50Hz), the noise filter is energised. Figure 0-1 on page 21 NOTE: When the oven door is opened, the oven lamp comes on at this time. 6. MONITOR SWITCH CIRCUIT The monitor switch (SW2) is mechanically controlled by oven door, and monitors the operation of the monitored latch switch (SW1) 6-1 When the oven door is opened during or after the cycle of a cooking program, the monitored latch switch (SW1) and stop switch (SW3)must open its contacts first. After that the contacts (COM - NC) of the monitor switch (SW2) can be closed. 6-2 When the oven door is closed, the contacts (COM - NC) of the monitor switch (SW2) must be opened first. The contacts (COM - NO) of the monitored latch switch (SW1) and stop switch (SW3) are closed after. 6-3 When the oven door is opened and the contacts of the monitored latch switch (SW1) remain closed, the fuse F1 will blow, because the monitor switch is closed and a short circuit is caused.

MICROWAVE COOKING CONDITION HIGH COOKING
Enter a desired cooking time with the touching TIME pad and start the oven with touching START pad.

Function sequence Figure 0-2 on page 21 CONNECTED COMPONENTS RELAY
Oven lamp, Fan motor, Turntable motor Power transformer RY1 RY2

HIGH, MEDIUM HIGH, MEDIUM, MEDIUM LOW, LOW COOKING
When the microwave oven is preset for variable cooking power, the line voltage is supplied to the power transformer intermittently within a 32-second time base through the vari contact. The following levels of microwave power are given. SETTING

1. The line voltage is supplied to the primary winding of the power transformer. The voltage is converted to about 3.3 volts A.C. output on the filament winding and high voltage of approximately 2000 volts A.C. on the secondary winding. 2. The filament winding voltage (3.3 volts) heats the magnetron filament and the high voltage (2000 volts) is sent to the voltage doubling circuit, where it is doubled to negative voltage of approximately 4000 volts D.C.. 3. The 2450 MHz microwave energy produced in the magnetron generates a wave length of 12.24 cm. This energy is channeled through the waveguide (transport channel) into the oven cavity, where the food is placed to be cooked. 4. When the cooking time is up, a single tone is heard and the relays RY1 + RY2 go back to their home position. The circuits to the oven lamp, power transformer, fan motor and turntable motor are cut off. 5. When the door is opened during a cook cycle, the switches come to the following condition.
CONDITION DURING DOOR OPEN COOKING (NO COOKING) Open Closed Closed Open

32 sec. ON HIGH 24 sec. ON MEDIUM HIGH 18 sec. ON MEDIUM 12 sec. ON MEDIUM LOW 6 sec. ON LOW 26 sec. OFF Approx. 10% = 80 Watts 20 sec. OFF Approx. 30% = 240 Watts 14 sec. OFF Approx. 50% = 400 Watts 8 sec. OFF 100% = 800 Watts Approx. 70% = 560 Watts

NOTE: The ON/OFF time ratio does not exactly correspond to the percentage of microwave power, because approx. 3 seconds are needed for heating up the magnetron filament.

SWITCH Monitor switch Monitored latch switch

CONTACT COM-NC COM-NO

The circuits to the power transformer, fan motor and turntable motor are cut off when the monitored latch switch is opened.

R-24STM - 6