Service manual

9
R-1855A
The time of supplementary cooking is determined by
experiment with each food category and inputted into the
LSI.
An example of how sensor works:
1. Potatoes at room temperature. Vapor is emitted very
slowly.
MICROWAVE
2. Heat potatoes. Moisture and humidity is emitted rapidly.
You can smell the aroma as it cooks.
MICROWAVE
AH SENSOR
3. Sensor detects moisture and humidity and calculates
cooking time and variable power.
Cooking Sequence.
1. Touch SENSOR COOK, SENSOR REHEAT or
POPCORN pad. When Sensor Cook is touched, to
choose menu the number pad should be touched.
NOTE: The oven should not be operated on SENSOR
COOK, SENSOR REHEAT or POPCORN
immediately after plugging in the unit. Wait five
minutes before cooking on SENSOR COOK,
SENSOR REHEAT or POPCORN.
2. The coil of shut-off relays (RY1, RY4 and RY5) are
energized, the oven lamp, turntable motor and cooling
fan motor are turned on, but the power transformer is not
turned on.
3. After about 32 seconds, the cook relay (RY2) is energized.
The power transformer is turned on, microwave energy
is produced and first stage is started.
The 32 seconds is the cooling time required to remove
any vapor from the oven cavity and sensor.
NOTE: During this first stage, do not open the door or touch
STOP/CLEAR pad.
4. When the sensor detects the vapor emitted from the
food, the display switches over to the remaining cooking
time and the timer counts down to zero.
At this time, the door may be opened to stir food, turn it
or season, etc.
5. When the timer reaches zero, an audible signal sounds.
The shut-off relay and cook relay are de-energized and
the power transformer, oven lamp, etc. are turned off.
6. Opening the door or touching the STOP/CLEAR pad, the
time of day will reappear on the display and the oven will
revert to an OFF condition.
COMPU BROIL, COMPU ROAST, COMPU BAKE
COMPU BROIL, COMPU ROAST and COMPU BAKE will
automatically compute the oven temperature, microwave
power and cooking time for broiling, roasting and baking. Set
the desired program by touching one of the COMPU BROIL,
COMPU ROAST or COMPU BAKE pad, and number pad.
Enter the weight by touching the Number pads. When the
START pad is touched, the following operations occur:
1. The COOK indicator will light and the CONV or MIX
indicator will light.
2. The cooking time will appear on the display and start
counting down to zero. The cooking time is adjusted
automatically according to the weight of the food.
3. The shut-off relays (RY1, RY4, RY5 and RY7) are
energized, turning on the oven lamp, turntable motor,
cooling fan motor and convection motor. The power
supply voltage is applied to the heating element.
4. Now, the oven is in the convection cooking mode or
Automatic Mix Cooking condition.
5. When the oven temperature has reached the
programmed convection temperature, the oven goes
into the programmed cooking mode.
6. At the end of the cooking cycle, the damper is returned
to the open position and the oven will go to the off
condition. The cooling fan will remain on until the oven
has cooled.
COMPU DEFROST COOKING
The COMPU DEFROST key is a special function key to
defrost meats and poultry faster and better. COMPU
DEFROST automatically defrosts roast beef, etc.. When
the COMPU DEFROST is selected and the food weight is
entered by using the COMPU DEFROST pad, the oven will
cook according to the special cooking sequence.
FIRE SENSING FEATURE (MICROWAVE MODE)
This model incorporates a sensing feature which will stop
the oven's operation if there is a fire in the oven cavity during
microwave cooking.
This is accomplished by the LSI repeatedly measuring the
voltage across the temperature measurement circuit (ther-
mistor) during it's 32-seconds time base comparing the
obtained voltage measurements. If the most recent voltage
measured is 100mV greater than the previous voltage
measured, the LSI judges it as a fire in the oven cavity and
switches off the relays to the power transformer and fan
motor. The LSI also stops counting down and closes the
damper plate so that no fresh air will enter the oven cavity.
Please refer to the following section for a more detailed
description.
Operation
The following operation will start 4 minutes after the start
pad is touched. Please refer to the timing diagrams below.
1. The thermistor operates within a 32-seconds time base
and it is energized for three (3) seconds and off for 29
seconds. Two (2) seconds after the thermistor is
energized, the voltage across the temperature
measurement circuit is sampled by the LSI and twenty
one (21) seconds after the thermistor is cut off the LSI
turns on the convection motor for six (6) seconds.
2. The above procedure is repeated. If the difference
between the first voltage measured (in step 1) and the
voltage measured when the procedure is repeated (step
2) is greater than 100mV the LSI makes the judgment
that there is a fire in the oven cavity and will switch off