SHARP R-770B
Service Manual

R-770B

TOP HEATER MODE In this mode, the food is cooked by the top heaters. Press the GRILL pad once and then enter the cooking time by pressing the number pads. When the START pad is pressed, the following operations occur: 1. 2. 3. 4. 5. Figure O-3(a) on page 27 The relay RY3 + RY5 + RY6 are energized. The numbers of the digital read-out start the count down to zero. Then the top heaters, turntable motor, oven lamp and fan motor are energized. Now, the food is grilled by the top heaters. Upon completion of the selected cooking time, audible signal sounds and the contacts of relays RY3 + RY6 are opened, then the top heaters, turntable motor and oven lamp are de-energized. But the relay RY5 stays closed and the fan motor operates for 5 minutes. But if the cooking time is less than 2 minutes the relay RY5 will not stay close.

GRILL MIX COOKING CONDITION The oven will cook food by supplying grill heaters (top heaters or Bottom heater) and microwave energy alternately within a 48 seconds time base. And the oven has four programmed cooking mode. GRILL MIX HIGH WITH TOP HEATER MODE AND GRILL MIX LOW WITH TOP HEATER MODE In these modes, the food is cooked by the top heaters and the microwave energy. Press the GRILL MIX pad once for GRILL MIX HIGH with TOP HEATER mode. Press the GRILL MIX pad twice for GRILL MIX LOW with TOP HEATER mode. And then enter the cooking time by pressing the number pads. When the START pad is pressed, the following operations occur: 1. 2. 3. Figure O-4(a) on page 29 The relay RY5 + RY6 are energized. The numbers of the digital read-out start the count down to zero. The turntable motor, oven lamp and fan motor are energized. The relay RY2 + RY3 are energized alternately within a 48 seconds time base by the control unit. The top heaters operate through the relay RY3 is energized. And the high voltage transformer operates through the relay RY2 is energized. The relationship between the top heating elements and magnetron operations are as follows.
26 SEC. ON (MICRO.) OFF MICROWAVE POWER = APPROX. 50% 22 SEC.

BOTTOM HEATER MODE In this mode, the food is cooked by the bottom heater. Press the GRILL pad twice and then enter the cooking time by pressing the number pads. When the START pad is pressed, the following operations occur: Figure O-3(b) on page 28 1. The relay RY4 + RY5 + RY6 are energized. 2. The numbers of the digital read-out start the count down to zero. 3. Then the bottom heater, turntable motor, oven lamp and fan motor are energized. 4. Now, the food is grilled by the bottom heater. 5. Upon completion of the selected cooking time, audible signal sounds and the contacts of relays RY4 + RY6 are opened, then the bottom heating elements, turntable motor and oven lamp are de-energized. But the relay RY5 stays closed and the fan motor operates for 5 minutes. But if the cooking time is less than 2 minutes the relay RY5 will not stay close. TOP AND BOTTOM HEATER MODE In this mode, the food is cooked by both the top heaters and bottom heater. Press the GRILL pad three times and then enter the cooking time by pressing the number pads. When the START pad is pressed, the following operations occur: Figure O-3(c) on page 28 1. The relay RY3 + RY4 + RY5 + RY6 are energized. 2. The numbers of the digital read-out start the count down to zero. 3. Then the top heaters, bottom heater, turntable motor, oven lamp and fan motor are energized. 4. Now, the food is grilled by the top heaters and the bottom heater. 5. Upon completion of the selected cooking time, audible signal sounds and the contacts of relays RY3 + RY4 + RY6 are opened, then the top heating elements, bottom heating element, turntable motor and oven lamp are de-energized. But the relay RY5 stays closed and the fan motor operates for 5 minutes. But if the cooking time is less than 2 minutes the relay RY5 will not stay closed. 4. 5.

6.

ON TOP HEATERS OFF

GRILL MIX HIGH with TOP HEATER mode
8 SEC. ON (MICRO.) OFF ON TOP HEATERS OFF MICROWAVE POWER = APPROX. 10% 40 SEC.

GRILL MIX LOW with TOP HEATER mode

Note:

The On/Off time ratio does not exactly correspond to the percentage of microwave power, because

approx. 2 seconds are needed for heating up the magnetron filament. 7. Upon completion of the selected cooking time, audible signal sounds and the contacts of relays RY2 + RY3 + RY6 are opened, then the top heaters, high voltage transformer, turntable motor and oven lamp are deenergized. But the relay RY5 stays closed and the fan motor operates for 5 minutes. But if the cooking time is less than 2 minutes the relay RY5 will not stay close. GRILL MIX HIGH WITH BOTTOM HEATER MODE AND GRILL MIX LOW WITH BOTTOM HEATER MODE IIn these modes, the food is cooked by the bottom heater and the microwave energy. Press the GRILL MIX pad three (3) times for GRILL MIX HIGH with BOTTOM HEATER mode. Press the GRILL MIX pad four (4) times for GRILL MIXLOW with BOTTOM HEATER mode. And then enter the cooking time by pressing the number pads.
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