OPERATION. Sharp CD2200M

RCD2200M

CHAPTER 5. OPERATION

Service Manual

[1] DESCRIPTION OF OPERATING SEQUENCE

The following is a description of component functions during oven operation.

1. OFF CONDITION

(For details, refer to Figure O-1)

Closing the door activates the door sensing switch and secondary interlock switches (1), (2). (In this condition, the monitor switches (1) &

(2) contacts are opened.) When the oven is plugged in, and the rated voltage is supplied to the switching power supply unit through the noise filter, (figure O-1). The switching supply unit supplies D.C. voltage (approx. 24V) to the relay unit. And the display will show “ . “.

2. COOKING CONDITION

(For details, refer to Figure O-2)

Press SELECT TIME pad. Enter cooking time by pressing the number pads. Press the SELECT POWER pad. Enter power level by pressing the number pad. When the START pad is pressed, the following operations occur:

1. The contacts of relays are closed. And the oven lamp and the antenna motors connected to the relays are turned on (For details, refer to Figure O-2).

2. D.C. voltage is supplied to the fan motors, exhaust fan and exhaust motor from the control unit.

3. Rated voltage is supplied to the primary winding of the power transformer and is converted to about 3.17 volts output on the filament winding, and approximately 2240 volts on the high voltage winding.

4. The filament winding voltage heats the magnetron filament and the

H.V. winding voltage is sent to a voltage doubler circuit.

5. The microwave energy produced by the magnetron is channelled through the waveguide into the cavity feed-box, and then into the cavity where the food is placed to be cooked.

6. Upon completion of the cooking time, the oven will revert to the

OFF condition. The fan motors, exhaust fan and the exhaust motor will operate at least for 1 minute.

7. When the door is opened during a cook cycle, monitor switches (1)

& (2), door sensing switch, secondary interlock switches (1), (2) and primary interlock relay are activated with the following results.

The circuits to the high voltage components are de-energized.

8. The monitor switch (1) is electrically monitoring the operation of the secondary interlock switch (1) and primary interlock relay, and monitor switch (2) is electrically monitoring the operation of the secondary interlock switch (2) and primary interlock relay, and monitor switches (1), (2) are mechanically associated with the door so that it will function in the following sequence.

1) (1) When the door opens from a closed position, the contacts of the primary interlock relay and secondary interlock switches (1),

(2) open. Then the monitor switch contacts close.

2) (2) When the door is closed from the open position, the monitor switches (1), (2) contacts first open, and then the contacts of the secondary interlock switches (1), (2) close.

If the secondary interlock switches (1), (2) and primary interlock relay fail with their contacts closed when the door is opened, the closing of the monitor switches (1), (2) contacts will form a short circuit through the monitor fuse, secondary interlock switches (1), (2) and primary interlock relay, causing the monitor fuse to blow.

3. DOOR OPEN CONDITION

When the door is opened, the contacts of the door sensing switch open, initiating the following:

1. A signal is input to the control unit energizing the coil of shutoff relay (RY-4).

2. The shut-off relay (RY-4) contacts close completing circuits to turn on the oven lamp and antenna motors.

3. If the door remains open, 60 seconds later the control unit de-energizes shut-off relay (RY-4) turning off the oven lamp and antenna motors.

4. VARIABLE POWER COOKING

When Variable Cooking Power is programmed, the rated voltage A.C.

is supplied to the power transformer intermittently through the contacts of relay (RY-2, RY-3). Relays RY-2 and RY-3 are operated by the control unit within an interval 48 second time base. Microwave power operation is as follows:

VARI-MODE ON TIME OFF TIME

90%

80%

70%

60%

50%

40%

30%

20%

10%

0%

44 sec.

40 sec.

36 sec.

32 sec.

26 sec.

22 sec.

16 sec.

12 sec.

8 sec.

0 sec.

4 sec.

8 sec.

12 sec.

16 sec.

22 sec.

26 sec.

32 sec.

36 sec.

40 sec.

48 sec.

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

5. TWO MAGNETRON OPERATION SYSTEM

Two magnetrons (1), (2) are equipped in order to get higher microwave power output. The primary windings of the power transformers

(1), (2) are connected so that each magnetron can be oscillated alternatively according to the frequency of the power supply. Refer to the

Figure B-1.

OPERATION OF

MAGNETRON

COMMERCIAL

FREQUENCY

(60HZ)

POWER OUTPUT

BY MAGNETRON 1

POWER OUTPUT

BY MAGNETRON 2

Figure B-1. Operation of Magnetron

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RCD2200M

[2] OVEN SCHEMATIC

1. Off Condition

SCHEMATIC

NOTE: CONDITION OF OVEN

1. DOOR CLOSED

2. “ . “ APPEARS ON DISPLAY

2. Cooking Condition

SCHEMATIC

NOTE: CONDITION OF OVEN

1. DOOR CLOSED.

2. SELECT TIME PAD TUCHED..

3. COOKING TIME PROGRAMMED.

4. START PAD TOUCHED.

Figure O-1. Oven Schematic-Off Condition

Figure O-2. Oven Schematic-Cooking Condition

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RCD2200M

[3] DESCRIPTION AND FUNCTION OF COMPONENTS

1. DOOR OPEN MECHANISM

1. The handle lever is pulled.

2. The upper and lower latch heads are lifted up by the linked latch lever.

3. The latch lever is lifted up by the handle lever.

4. Now both latch heads are lifted up, so they can be released from the latch hook.

5. Now the door can be opened.

Handle lever

Latch lever

Latch head

Latch head

Switch lever A

Latch hook

Monitor switch (2)

Monitor switch (1)

Switch lever B

Secondary interlock switch (2)

Secondary interlock switch (1)

Door sensing switch

Switch lever C

Figure D-1. Door Open Mechanism

2. DOOR SENSING SWITCH

The door sensing switch is activated by the latch head of the door and switch lever C. When the door is opened, the contacts of the switch open and interrupt the circuit to the coils of the primary interlock relay.

The contacts of the primary relay then open and interrupt the circuit to the primary winding of the power transformers.

3. SECONDARY INTERLOCK SWITCHES (1), (2)

The secondary interlock switches (1), (2) are activated by the upper latch head of the door and switch lever B. When the door is opened, the contacts of the switch open and interrupt the circuit to the primary winding of the power transformers (1), (2).

4. MONITOR SWITCHES (1), (2)

The monitor switches (1), (2) are mounted in the upper position of the latch hook. The monitor switches are activated by the upper latch head of the door and switch lever A. When the door is opened, the contacts of the monitor switches close. Monitor switch (1) 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

(1) fail to open when the door is opened. Monitor switch (2) 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 (2) fail to open when the door is opened.

Functions:

With the door shut, the contacts of the door sensing switch and the secondary interlock switches (1), (2) are closed and the contacts of the monitor switches (1), (2) are open.

1. When the door is opened, the contact of the door sensing switch and secondary interlock switches (1), (2) are opened first, then the contact of the monitor switches (1), (2) are closed.

2. As the door goes to a closed position, the contacts of the monitor switches (1), (2) are opened first, then the contacts of the door sensing switch and the secondary interlock switches (1), (2) close.

3. If the door is opened, and the contacts of the primary interlock relay and secondary interlock switch of the same circuit fail to open, the monitor fuse blows simultaneously with closing of the monitor switch contacts of that circuit (1 or 2).

CAUTION: BEFORE REPLACING A BLOWN MONITOR FUSE TEST

THE DOOR SENSING SWITCH, PRIMARY INTERLOCK

RELAY, SECONDARY INTERLOCK SWITCHES (1), (2),

DOOR SENSING SWITCH AND MONITOR SWITCHES

(1), (2) FOR PROPER OPERATION. (REFER TO CHAP-

TER “TEST PROCEDURE”).

NOTE: MONITOR FUSE AND SWITCH ARE REPLACED AS AN

ASSEMBLY.

5. MONITOR FUSE

1. The monitor fuse blows when the contacts (COM-NO) of the primary interlock relay (RY1) and secondary interlock switch remain closed with the oven door open and when the monitor switch closes.

2. If the wire harness or electrical components are short-circuited, this monitor fuse blows to prevent an electric shock or fire hazard.

6. MAGNETRON TEMPERATURE FUSES (1), (2)

The temperature fuses (1), (2) located on the top of the upper and lower waveguide, are designed to prevent damage to the magnetrons

(1), (2). If an over heated condition develops in the tube due to blower motor failure, obstructed air ducts, dirty or blocked air intake, etc., the circuit to the magnetrons are interrupted. Under normal operation, the temperature fuses remains closed. However, when abnormally high temperatures are generated within the magnetron, the temperature fuse will open at 302 °F (150°C) causing the microwave energy to stop.

The defective temperature fuse must be replaced with new rated one.

7. OVEN TEMPERATURE FUSE

The temperature fuse, located on the side of the exhaust duct assembly, is designed to prevent damage to the oven by fire. If the food load is overcooked, by either error in cook time or defect in the control unit, the temperature fuse will open. Under normal operation, the oven temperature fuse remains closed. However, when abnormally high temperatures are generated within the oven cavity, the oven temperature fuse will open at 248 °F (120°C), causing the oven to shut down. The defective temperature fuse must be replaced with new rated one.

8. EXHAUST THERMISTOR

The exhaust thermistor is located on the side of the exhaust duct assembly. The temperature in the exhaust duct is detected through the resistance of the thermistor. If the temperature is high, the control panel will display”EE7” and the oven will stop to avoid overheating and catching fire. If the thermistor is open, the control panel will display

“EE8” and the oven will stop.

9. MAGNETRON THERMISTOR

The thermistor is a negative temperature coefficient type. The air temperature around the upper and lower magnetrons is detected through the resistance of the thermistor. If the temperature is high, the control panel will display “EE7” and the oven will stop to protect the magnetrons against overheat. If the magnetron thermistor is open, the control panel will display “EE8” and the oven will stop.

10. FAN MOTORS

The fan motors drive blades which draw external cool air into the oven.

This cool air is directed through the air vanes surrounding the magnetrons and cools the magnetrons. This air is channelled through the oven cavity to remove steam and vapours given off from the heating foods. It is then exhausted through the exhausting air vents at the oven cavity.

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RCD2200M

During cooking, they operate. After cooking, they will operate at least for 1 minute and the maximum operating time is 4 minutes. When the temperature of the magnetron thermistor becomes bellow 110 °C, the fan motors will stop. These two (2) fan motors are D.C. motors.

11. EXHAUST MOTOR

The exhaust motor is located on the side of the exhaust duct assembly. This motor drives a blade in the exhaust duct assembly. The driven blade draws the external cool air into the oven from the intake duct assembly. Then it sends the air out of the oven through the exhaust duct assembly. During cooking, the exhaust motor operates.

After cooking, it will operate at least for 1 minute and the maximum operating time is 4 minutes. When the temperature of the exhaust thermistor becomes bellow 65 °C, the exhaust motor will stop. This motor is D.C. motor.

NOTE: Do not disconnect the power supply from the exhaust motor when it is turned on. Or it may be out of order.

12. ANTENNA MOTORS

The upper and lower antenna motors drive antennas to radiate the microwave.

13. EXHAUST FAN

The exhaust fan is located to the rear cover. It sends the air (which is at the top of the oven cavity) out of the oven. This motor is D.C. motor.

14. ANTENNA SENSOR

The antenna sensors are located to the top and bottom of the oven cavity. And they watch if the antennas are rotating or not.

15. MIROWAVE SENSOR

The microwave sensor is located on the top of the oven cavity. And it watch if the microwave is radiated into the oven cavity or not.

16. FUSE 12A (1) (2)

1. If the wire harness or electrical components are short-circuited, this fuse blows to prevent an electric shock or fire hazard.

2. The fuse also blows when the asymmetric rectifier, H.V. rectifier,

H.V. wire harness, H.V. capacitor, magnetron or secondary winding of high voltage transformer is shorted.

17. H.V. ASYMMETRIC RECTIFIER (1) (2)

The H.V.asymmetric rectifiers (1) (2) are solid state devices that prevent current flow is both directions. And they prevent the temperature rise of the high voltage transformers (1) (2) by blowing the fuses 12A

(1) (2) when the high voltage rectifiers (1) (2) are shorted. The rated peak reverse voltage of D1 of the asymmetric rectifier is 6 KV. The rated peak reverse voltage of D2 of the asymmetric rectifier is 1.7 KV.

D1 and D2 of the asymmetric rectifier or high voltage rectifier are shorted when the each peak reverse voltage goes beyond the each rated peak reverse voltage. (The process of the blowing the fuse 12A.)

D2 D1

ASYMMETRIC

RECTIFIER

HIGH VOLTAGE

RECTIFIER

NOTE: The H.V.asymmetric rectifier is assembled with the high voltage rectifier actually.

1. The high voltage rectifier is shorted by some fault when microwave cooking or dual cooking.

2. The peak reverse voltage of D2 of the rectifier goes beyond the rated peak reverse voltage 1.7 KV in the voltage doubler circuit.

3. D2 of the rectifier is shorted.

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4. The large electric currents flow through the high voltage winding of the high voltage transformer.

5. The large electric currents beyond 12A flow through the primary winding of the high voltage transformer.

6. The fuse 12A blows by the large electric currents.

7. The power supplying to the high voltage transformer is cut off.

18. OVEN LAMP

The oven cavity light illuminates the interior of the oven so that food being cooked can be examined visually through the door window without having to open the door.

19. NOISE FILTER

The noise filter prevents the radio frequency interference that might flow back in the power circuit.