R939(W)
6 – 2
the asymmetric rectifier is 1.7 KV. D1 and D2 of the asymmetric recti-
fier or high voltage rectifier are shorted when the each peak reverse
voltage goes beyond the each rated peak reverse voltage. (The pro-
cess of the blowing the fuse F2 F8A.)
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.
4. The large electric currents flow through the high voltage winding of
the high voltage transformer.
5. The large electric currents beyond 8A flow through the primary
winding of the high voltage transformer.
6. The fuse F2 F8A blows by the large electric currents.
7. The power supplying to the high voltage transformer is cut off.
[12] NOISE FILTER
The noise filter assembly prevents radio frequency interference that
might flow back in the power circuit.
[13] TURNTABLE MOTOR (TTM)
The turntable motor rotates the turntable.
[14] FAN MOTOR (FM)
The fan motor drives a blade which draws external cool air. This cool
air is directed through the air vanes surrounding the magnetron and
cools the magnetron. This air is channelled through the oven cavity to
remove steam and vapours given off from heating food. It is then
exhausted through the exhausting air vents of the oven cavity.
[15] CONVECTION MOTOR (CM)
The convection motor drives the convection fan and provide the
heated air.
[16] GRILL HEATING ELEMENT (GH)
The grill heating elements are provided to brown the food and are
located on the top of the oven cavity.
[17] CONVECTION HEATING ELEMENT
(CH)
The convection heating element situated at the rear of the oven cavity.
It is intended to heat air driven by the convection fan. The heated air is
kept in the oven and force-circulated and reheated by the convection
heating element.
[18] CONVECTION COOKING SYSTEM
This oven is designed with a hot air heating system where food is
heated by forced circulation of the hot air produced by the grill heaters.
The air heated by the grill heating elements is circulated through the
convection passage provided on the outer casing of the oven cavity by
means of the convection fan which is driven by the convection motor. It
is then enters the inside of the oven through the vent holes provided
on the back side of the oven. Next, the hot air heats the food on the
turntable and leaves the oven cavity through the vent in the oven cav-
ity rear wall. In this way, the hot air circulates inside the oven cavity to
raise its temperature and, at the same time, comes into contact with
the food being cooked. When the temperature inside the oven cavity
reaches the selected temperature, the heating elements are de-ener-
gized. When the temperature inside the oven cavity drops below the
selected temperature, the heating elements are energized again. In
this way, the inside of the oven cavity is maintained at approximately
the selected temperature.
When the convection time reaches “0”, the heating elements are deen-
ergized and the convection fan stops operating and the oven shuts off.
At that time if the cavity air temperature has risen above 120
°
C, the
fan motor remains rotating. Automatically the fan motor will be shut
down at low temperature (less than 105
°
C).
Figure D-2. Convection Cooking System
[19] FIRE SENSING FEATURE
The oven will stop its operation when there is a fire in the oven cavity
in microwave cooking condition. LSI measures the voltage across the
temperature measurement circuit intermittently within 32-seconds time
base since the oven is started in microwave cooking condition. The
oven will stop its operation when the difference of the voltage is more
than 0.39 volts in microwave cooking condition.
1. Within a 32-seconds base, the thermistor is energized for 2 sec-
onds. At that time, the voltage across the temperature measure-
ment circuit is measured.
2. The oven carries out the procedure above again. If the second volt-
age is 0.39V higher than first voltage, LSI judges it is a fire in the
oven cavity and stop the oven.
3. When LSI judges it is a fire in the oven cavity, LSI will switch off the
relays to high voltage transformer and fan motor and LSI stops
counting down.
[20] OPEN JUDGE BY THERMISTOR
1. If the temperature of the thermistor does not rise to more than 40
°
C
after 4 minutes and 15 seconds from when the oven is started in
convection, grill or dual cooking mode, the oven is turned off.
2. When the thermistor or the wire harness to the thermistor is
opened, the oven is turned off after 4 minutes and 15 seconds
because this condition is same as above.
[21] DAMPER OPEN-CLOSE MECHANISM
Damper position is set automatically by damper motor DM, damper
switch and motor cam. These components are operated by a signal
that judges if microwave cooking or convection cooking operation is
selected by the CPU unit.
Door
Oven Cavity
Grill Heating
Elements
Convection
Passage
Cooling
Fan
Convection
Motor
Convection
Fan
Turntable
Turntable Motor
Roller Stay
Convection
Heating Element
THERMISTOR
Sensing
Voltage
ON
OFF
ON
OFF
Sensing the voltage across temperature measurement circuit.
Summary of Contents for R-939(BK)
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