Sharp R-2397 service manual Operation Sequence, OFF Condition, Microwave Cooking Condition

R-2397

OPERATION SEQUENCE

OFF CONDITION

Closing the door activates all door interlock switches

(1st latch switch, 2nd latch switch, 3rd latch switch and stop switch)

IMPORTANT

When the oven door is closed, the monitor switch contacts COM-NC must be open. When the microwave oven is plugged in a wall outlet (230 volts, 50Hz), the line voltage is supplied to the point A5+A7 in the control panel.

Figure O-1 on page 30

1. The digital display shows .

NOTE: When the door is opened or after cooking, oven lamp, blower motor and stirrer motors work for 1 minute.

MICROWAVE COOKING CONDITION

Touch MANUAL/ REPEAT key and enter a desired cooking time with the touching NUMBER key. And then touch START key.

Function sequence Figure O-2 on page 30

CONNECTED COMPONENTS	RELAY
Oven lamp/ Blower motor/ Stirrer motors	RY1
Power transformer (rear)	RY3
Power transformer (front)	RY4

1.The line voltage is supplied to the primary winding of the high voltage 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 channelled 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 signal tone is heard and the relays RY3+RY4 go back to their home position. The circuits to the high voltage transformers. The relay RY1 remains and oven lamp, blower motor and stirrer motors work for 1 minute.

5.When the door is opened during a cook cycle, the switches come to the following condition.

		CONDITION
		DURING	DOOR OPEN
SWITCH	CONTACT	COOKING	(NO COOKING)
1st latch switch	COM-NO	Closed	Open
Monitor switch	COM-NC	Open	Closed
2nd latch switch	COM-NO	Closed	Open
Stop switch	COM-NO	Closed	Open
3rd latch switch	COM-NO	Closed	Open

the relay RY1 stays closed. Shown in the display is the remaining time, but the program is cancelled if the oven is not started within 3 minutes.

6. MONITOR SWITCH CIRCUIT

The monitor switch is mechanically controlled by oven door, and monitors the operation of the 1st latch switch.

6-1. When the oven door is opened during or after the cycle of a cooking program, the 1st, 2nd, 3rd latch and stop switches must open their contacts first. After that the contacts (COM-NC) of the monitor switch can be closed.

6-2. When the oven door is closed, the contacts (COM-NC) of the monitor switch must be opened first. After that the contacts (COM-NO) of the 1st, 2nd, 3rd latch and stop switches must be closed.

6-3. When the oven door is opened and the contacts of the 1st latch switch remain closed, remains closed, the fuse F6.3A will blow, because the monitor switch is closed and a short circuit is caused.

MICROWAVE VARIABLE COOKING

When the microwave oven is preset for variable cooking power, the line voltage is supplied to the high voltage transformers intermittently within a 48 second time base through the contacts of the relays RY3+RY4.

The following levels of microwaves power are given.

48 sec. ON

Number key

44sec. ON

Number key 9

40 sec. ON

Number key 8

36 sec. ON

Number key 7

32 sec. ON

Number key 6

26 sec. ON

Number key 5

22 sec. ON

Number key 4

16 sec. ON

Number key 3

12 sec. ON

Number key 2

8 sec. ON

Number key 1

0 sec. ON

Number key 0

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

TWO MAGNETRON OPERATION SYSTEM

The circuits to the high voltage transformers are cut off when the 1st latch, 2nd latch, 3rd latch and stop switches are made open. The blower motor, stirrer motors and oven lamp remains on even if the oven door is opened after the cooking cycle has been interrupted, because

Two magnetrons MG1+MG2 are equipped in order to get higher microwave power output. The primary windings of the high voltage transformers T1+T2 are connected so that each magnetron can be oscillated alternatively according to the frequency of the power supply. Refer to the Figure 1 and 2.

4